Download the ecology and microbiology of Vibrio cholerae

REVIEWS REVIEWS REVIEWS
80
Environmental microbe and human
pathogen: the ecology and microbiology
of Vibrio cholerae
Kathryn L Cottingham1, Deborah A Chiavelli1,2, and Ronald K Taylor2
Vibrio cholerae, the bacterium that causes cholera, is a fascinating microorganism that occupies two distinct
habitats: aquatic environments and human intestines. Although its activity in human hosts has received a
great deal of attention because of its effect on human health, the microbe’s behavior in natural ecosystems
has received much less consideration. In this paper we briefly review the microbiology and ecology of
V. cholerae, before highlighting four important areas for further research. First, V. cholerae acts as a typical
heterotrophic bacterium while in aquatic environments, mineralizing organic matter for reuse within the
food web. In addition, three key processes affect the microorganism’s population dynamics and therefore its
role in ecosystem processes: a viable-but-non-culturable (VBNC) state, attachment to environmental substrates, and bacterivory. Several factors link V. cholerae in its human and aquatic habitats, especially human
activities that influence its growth conditions while outside the body. These activities create feedbacks
between humans and the environment that are at present not well understood, but which are likely to alter
the persistence and spread of the resulting disease.
Front Ecol Environ 2003, 1(2), 80–86
C
holera is a more persistent and global health problem
now than it was a few decades ago (Colwell 1996).
This infectious disease is endemic in areas such as India and
Bangladesh, and is emerging or re-emerging elsewhere,
particularly in developing nations with inadequate sanitation (Faruque et al. 1998). Cholera outbreaks often
accompany natural disasters and destabilization due to wars,
even in non-endemic areas (Faruque et al. 1998), while
climate change and increased globalization will put additional areas at risk for future outbreaks (Ruiz et al. 2000;
Harvell et al. 2002). Taken together, these observations suggest that an improved understanding of the factors controlling cholera outbreaks would be beneficial to human health
worldwide.
Cholera is one of many human diseases with a substantial environmental component. The disease begins with
In a nutshell:
• Vibrio cholerae, the bacterium that causes cholera, exists in
both human intestines and aquatic ecosystems
• Human activity and the resulting ecological changes directly
affect the bacterium’s persistence and spread in aquatic
environments
• Research described here on the behaviour of V. cholerae
outside the body will help the development of strategies to
combat this worldwide health problem
1
Department of Biological Sciences, Dartmouth College,
Hanover, NH 03755 ([email protected]); 2Department of Microbiology and Immunology, Dartmouth Medical
School, Hanover, NH 03755
www.frontiersinecology.org
the ingestion of the causal bacterium Vibrio cholerae
(Figure 1) via contaminated water or food. The microbe
makes its way to the small intestine, where it attaches
and begins to produce cholera toxin (CT). Sufficient
quantities of CT cause severe diarrhea and the shedding
of many bacteria into the environment – up to 1013 per
infected individual per day (Mintz et al. 1994), facilitating disease spread. Although scientists had long thought
that the bacterium survived outside mammalian
intestines only for brief periods, research in the past few
decades shows that V. cholerae are an abundant, naturally
occurring component of freshwater, estuarine, and
marine ecosystems worldwide (Islam et al. 1997). As
such, the bacterium inhabits two very distinct habitats –
human hosts and aquatic ecosystems – and is tremendously flexible in its activities in order to survive in each
habitat. We need a much better understanding of the
relationship between the dynamics of V. cholerae in
humans and aquatic environments.
Microbiology and pathogenesis
Microbiological studies of V. cholerae began with its identification as the causal agent of cholera in 1884. Since
then, we have learned a great deal about its biochemistry,
genetics, and behavior in the human host (Faruque et al.
1998; Reidl and Klose 2002). Although there are more
than 200 known serogroups of V. cholerae, only two, O1
and O139, are known to cause epidemic disease (Faruque
et al. 1998; Reidl and Klose 2002). Strains from these
closely related groups have very similar antigens on their
© The Ecological Society of America
Ecology and microbiology of Vibrio cholerae
outermost layers, suggesting that surface
properties are a key component in the
ability to cause disease.
Historically, cholera outbreaks were
caused by V. cholerae O1, but O139
became the major cause of epidemic
cholera in some regions during the 1990s
(Faruque et al. 1998). The O1 serogroup
is further divided into two biotypes: classical and El Tor. Classical strains predominated in clinical samples until El
Tor was identified in 1961. Since then,
El Tor strains have gradually displaced
classical strains throughout much of the
world (Colwell 1996; Faruque et al.
1998). Whether these shifts between the Figure 1. Vibrio cholerae.
O1 classical, O1 El Tor, and O139
strains are related to environmental fitness, altered patho- level and attachment could affect their relative vulneragenicity, increased transmissibility, or other factors is not bility to grazers.
yet known.
Since most environmental strains of V. cholerae do not Viable but not culturable
cause epidemic disease in humans, an interesting question is how epidemic strains arise. Horizontal gene trans- As described by microbiologists, the viable-but-non-culmission through bacteriophages (viruses that infect bac- turable (VBNC) state is a response to rapid transitions in
teria) and other vectors plays a major role in creating environmental conditions, including temperature and
pathogenic V. cholerae by conveying genes involved in osmolarity (McDougald et al. 1998). When a bacterial
the colonization of humans and the production of cholera cell enters a VBNC state, it loses its flagellum and
toxin (Islam et al. 1997). The most critical genes are clus- changes to a smaller, spherical form (McDougald et al.
tered together in two regions of the bacterial genome – a 1998; Huq et al. 2000). VBNC cells do not reproduce on
pathogenicity island and a lysogenic bacteriophage standard microbiological media, and have decreased
(Faruque et al. 1998). The vibrio pathogenicity island nucleic acid content and reduced respiration and meta(VPI) encodes a number of genes, including those bolic rates (McDougald et al. 1998). The VBNC pherequired to express the toxin coregulated pilus (TCP), nomenon has been described for a number of pathogenic
which is essential for intestinal colonization. The lyso- bacteria, including V. cholerae, V. vulnificus, Escherichia
genic bacteriophage CTX-, which harbors the genes for coli, and Campylobacter jejuni (McDougald et al. 1998).
cholera toxin, uses the TCP to enter only those strains of Laboratory experiments indicate that V. cholerae can exist
V. cholerae capable of colonizing humans. It then lysoge- in the VBNC state for long periods, presumably allowing
nizes invaded cells by integrating its entire genome into them to survive unfavorable environmental conditions
that of the host bacterium. Thus, a partnership between (Huq et al. 2000).
The VBNC state is of critical importance to public
CTX- and V. cholerae expressing TCP is required to
health microbiologists, who need to be able to reliably
cause a cholera epidemic.
detect V. cholerae and other pathogenic bacteria in the
environment, particularly since VBNC cells can cause dis Ecology of V. cholerae
ease (Colwell et al. 1996). Consequently, both antibodyIn aquatic environments, V. cholerae probably acts as a and nucleic-acid-based approaches have been developed
typical heterotrophic bacterium. These microorganisms, to detect pathogens in natural waters, regardless of their
which cannot synthesize their own food, are responsible culturability (Theron and Cloete 2002). These methods
for much of the mineralization of organic matter, and have identified V. cholerae in the VBNC state in the
can be important components of aquatic food webs and majority of water and plankton samples tested (Huq et al.
nutrient cycles (Cole 1999; Cotner and Biddanda 1990; Huq et al. 2000), with a higher incidence of cultur2002). Like other organisms, bacteria react to environ- able V. cholerae during outbreak periods in both
mental conditions by increasing or decreasing their Bangladesh and Peru (Huq et al. unpublished).
metabolic rates, and can enter dormant and/or non-culThe VBNC state is controversial, however, because
turable states. They can also change the quality of their researchers do not yet agree on whether it is reversible.
microhabitat by switching between free-living (unat- Can cells be resuscitated from a VBNC state after envitached) and surface-attached forms and by aggregating ronmental conditions improve, or do the few remaining
into biofilms while attached. Importantly, both activity culturable cells simply regrow (McDougald et al. 1998;
© The Ecological Society of America
www.frontiersinecology.org
81
Courtesy of Louisa Howard, Thomas Kirn, and Niranjan Bose
KL Cottingham et al.
Ecology and microbiology of Vibrio cholerae
82
Kell et al. 1998)? Findings to date are equivocal, but
resolving this controversy is important to how we interpret field measurements of bacterial abundance, and how
we relate dynamics in the aquatic environment to human
disease outbreaks. For example, if VBNC V. cholerae can
be resuscitated (as demonstrated by Wai et al. 1996), then
the factors that trigger the transition back to an active,
culturable state are likely to be very important to both
cholera epidemiology and ecosystem processes.
Attachment
Like other heterotrophic bacteria, V. cholerae has been
found attached to a wide variety of aquatic organisms,
especially plankton (Table 1; Figure 2). Although attachment to a living host increases V. cholerae’s survival and
growth in the laboratory (Huq et al. 1984a; Islam et al.
1999), its effect on natural microbial populations or
ecosystem processes is not known. The surfaces of planktonic organisms are resource-rich microhabitats, since
V. cholerae can metabolize chitin, the surface material of
crustacean zooplankton, and mucilage from the outer surfaces of some phytoplankton (Islam et al. 1994). Living
plankton also supply nutrients to bacteria through excretion or exudates (Islam et al. 1994), while host movement
may prevent the depletion of nutrients in the surrounding
water (Threlkeld et al. 1993). Furthermore, various
plankton offer very different substrate qualities for
attached V. cholerae (Tamplin et al. 1990). For example,
copepods offer a more stable attachment substrate than
cladocerans, since copepods have a terminal molt stage
while cladocerans molt throughout their lifetimes.
Phytoplankton, on the other hand, provide a very nutrient-rich habitat, especially nitrogen-fixing taxa like
Anabaena (Islam et al. 1994).
The macroscopic detrital aggregates known as “marine
snow” and “lake snow” (Figure 3) may also provide a habi-
KL Cottingham et al.
Table 1. Organisms to which Vibrio cholerae is known
to attach
Phytoplankton
Cyanobacteria – Anabaena
Chlorophytes – Volvox, desmids, Rhizoclonium
Diatoms – Skeletonema
Dinoflagellates
Zooplankton
Copepods – Acartia, Cyclops, Diaptomus
Cladocerans – Daphnia, Bosmina, Bosminopsis,
Ceriodaphnia, Diaphanosoma, rotifers
Macrophytes
Marine taxa – Ulva, Entermorpha, Ceramium,
Polysiphonia
Freshwater taxa – Eichhornia (water hyacinth),
Lemna (duckweed)
Benthos
Prawns – Penaeus, Metapenaeus, Macrobrachium
Oysters
Crabs
Chironomid egg masses
Fish
Sea mullet
Tamplin et al. 1990; Huq et al. 1990; Islam et al. 1994; Colwell 1996
tat for attached V. cholerae, although this possibility is only
beginning to be explored. Work with non-pathogenic taxa
indicates that detrital aggregates provide resource-rich
microhabitats, to the extent that their associated bacteria
can account for a large fraction of microbial productivity in
the open ocean (Azam et al. 1994; Grossart and Simon
1998). To date, microbial ecologists have overlooked live
plankton as potential hosts for highly productive bacterial
communities, while microbiologists are only beginning to
consider whether V. cholerae attaches to detrital aggregates
– perhaps because microbial ecology tends to focus on bacteria as decomposers, while microbiology focuses on
host–parasite interactions.
Once attached to either living
hosts or detrital aggregates, the complexity of bacterial communities
varies from unassociated cells to wellorganized, three-dimensional structures called biofilms (Davey and
O’Toole 2000; Figure 4). Biofilms
increase bacterial productivity and
can provide protection from harmful
environmental conditions, including
chlorination and antibiotics (O’Toole
et al. 2000; Davey and O’Toole 2000).
V. cholerae biofilm activity may occur
on both planktonic and detrital substrates, but it is virtually unstudied
under natural conditions. However,
laboratory studies suggest that biofilm
activity affects V. cholerae abundance,
Figure 2. V. cholerae expressing green fluorescent protein (a) attached to and (b) in the growth rate, and persistence in poor
gut of the cladoceran filter-feeder Daphnia.
conditions (Yildiz and Schoolnik
www.frontiersinecology.org
© The Ecological Society of America
KL Cottingham et al.
Ecology and microbiology of Vibrio cholerae
1999; Haugo and Watnick 2002) – factors
that are likely to be important in aquatic
environments.
The effects of water quality and surface
material on attachment, and later detachment, remain a key question in cholera epidemiology. Several studies have evaluated
V. cholerae attachment under different physical
and chemical conditions (Huq et al. 1984b;
McCarthy 1996; Hood and Winter 1997;
Chiavelli et al. 2001), although none address
interactions between factors. Like the VBNC
state, attachment appears to be an adaptive
response to suboptimal conditions. At present,
however, we know very little about the individual contributions of the VBNC state and
attachment to the dynamics of V. cholerae in
aquatic ecosystems, and even less about how
these processes interact. To complicate the situation still further, both processes are likely to
affect bacterivory – the consumption of bacteria by other microorganisms.
Bacterivory
Bacterivores, including heterotrophic
nanoflagellates, protozoans, rotifers, and
cladocerans, may strongly regulate bacterial
populations (Cole 1999; Jürgens and Matz
2002). Bacterivory is most important in situ- Figure 3. Bacteria attached to marine snow from the German Waddensea,
ations where predation rates exceed bacterial visualized using SybrGold staining (x400).
population growth rates. The extent to
which V. cholerae population dynamics are regulated by copepods do not generally feed on bacteria (Cole 1999).
bacterivores has not yet been investigated. However, we Attachment to plankton or detritus should provide a
hypothesize that activity level and attachment status refuge from grazers, regardless of activity level, since bacaffect the rates of consumption of V. cholerae, since graz- teria attached to surfaces are less vulnerable to predation
ing on non-pathogenic bacteria is a function of bacterial (Cole 1999).
activity, bacterial cell size, and grazer size (Cole 1999;
Jürgens and Matz 2002). For example, protistan grazers Linking the environment to outbreaks
selectively remove active cells, while cladocerans feed
indiscriminately on both active and inactive (VBNC) In areas where cholera is endemic, disease outbreaks
cells (Cole 1999; Langenheder and Jürgens 2001). begin when humans are infected with V. cholerae from the
However, protists can be limited by bacterial size, so that environment, and may then be accelerated by fecal contcells larger than 2.4 m are rarely grazed (Pernthaler et al. amination (Franco et al. 1997). There are typical seasonal
1996). V. cholerae is rod-shaped and measures approxi- patterns to endemic outbreaks (Colwell 1996). In parts of
mately 3 m long by 1 m wide when active, and Bangladesh, for example, there is usually one outbreak
becomes a sphere of about 1 m in diameter when in the before the monsoons (March–June) and a second, larger
outbreak following the monsoons (September–
VBNC state.
We believe that filter-feeding cladoceran zooplankton December) (Islam et al. 1993; Longini et al. 2002). In
like Daphnia, but not protists, graze active V. cholerae due Peru, outbreaks occur annually, following spring warming
to their large size. In contrast, V. cholerae in the VBNC (Franco et al. 1997). Outbreaks in endemic areas are
state should be vulnerable to grazing by both protists and often geographically localized (Tauxe et al. 1994; Faruque
cladocerans, based on size constraints, although protists et al. 1998) and appear to coincide with seasonal changes
may not select inactive cells. Furthermore, we suggest that in plankton abundance (Islam et al. 1994; Colwell 1996;
zooplankton communities dominated by Daphnia are bet- Lobitz et al. 2000).
Despite the apparent relationship between cholera outter at reducing the abundance of free-living V. cholerae
populations than copepod-dominated communities, since breaks and plankton numbers, it is unclear whether plank© The Ecological Society of America
www.frontiersinecology.org
Courtesy of Hans-Peter Grossart
83
Ecology and microbiology of Vibrio cholerae
KL Cottingham et al.
aquatic environment (Faruque et al. 1998), and then be
enhanced in their infectivity by a trip through a human
host (Merrell et al. 2002).
84
Courtesy of Paula Watnick
Anthropogenic effects
Figure 4. V. cholerae biofilm.
ton blooms actually cause cholera outbreaks, since a large
number of physical, chemical, and biological factors differ
during outbreak periods. For example, seasonal cholera
outbreaks in Bangladesh coincide with times of both high
nutrient availability and high plankton populations
(Colwell 1996), either of which could increase V. cholerae
abundance. However, it is not clear whether V. cholerae is
responding to improved water conditions, more plankton
surfaces, more of a particular kind of plankton, or other
factors. Careful monitoring and statistical analyses of all
relevant physical, chemical, biological, and epidemiological variates, followed by experimental manipulation of the
putative causal factors, is needed to untangle the triggers
of cholera outbreaks.
The potential for an environmental reservoir of
pathogenicity genes is a second important link between
V. cholerae in aquatic ecosystems and those attacking
human hosts (Faruque et al. 1998; Reidl and Klose 2002;
Faruque and Nair 2002). Interestingly, many V. cholerae
isolated from the environment, including strains other
than the epidemic-associated O1 or O139 serogroups, contain the VPI and CTX- ( Faruque and Nair 2002).
Whether these strains serve as precursors to epidemic
strains or as a source for pathogenesis genes that can be
transferred to O1 or O139 strains is not yet known, but at
least some of the environmental strains that harbor the
pathogenicity genes are capable of infection in an infant
mouse cholera model (Boyd and Waldor 2002). Thus, new
clones capable of causing disease may emerge from the
www.frontiersinecology.org
Humans have the potential to affect V. cholerae abundance and transmission at multiple spatial scales. At a
local scale, any human activities that alter water characteristics, such as temperature and nutrient concentrations, may affect V. cholerae directly, by altering conditions for growth, or indirectly, by altering the
distribution, abundance, and composition of the plankton (and therefore the potential for attachment or bacterivory). Such activities include land-use change, pollution (including sewage), aquaculture and fisheries
management, the introduction of exotic species, and the
reduction of biodiversity.
On a broader spatial scale, human-induced climate
change could alter V. cholerae dynamics by changing the
microbe’s seasonal regimes or facilitating its spread to new
areas. Effects of climate variability on cholera are already
documented (Pascual et al. 2002); outbreaks occur during
periods of higher lake and river temperatures (Franco et al.
1997) and higher sea surface temperature and height
(Lobitz et al. 2000), and have been linked to the El Niño
Southern Oscillation (Pascual et al. 2000). Cholera
dynamics could be further altered by changes in
drought–monsoon cycles and rising sea levels, both of
which are expected under current climate change scenarios (Patz and Khaliq 2002). In addition, increased global
temperatures could promote colonization or establishment
of epidemic strains in new areas, as has happened for other
diseases (Harvell et al. 2002).
Finally, long-distance transmission through a globalized
economy appears increasingly likely. Past cholera epidemics have been linked to ballast water transmission,
international food transport, and travelers moving from
endemic to non-endemic areas of infection (Tauxe et al.
1994). As each of these activities continues to increase,
we need to better understand the feedbacks between
human activities, V. cholerae in the environment, and
cholera outbreaks.
Perspectives
The persistence of V. cholerae in aquatic environments,
the lack of an effective vaccine, and increasing antibiotic
resistance among strains isolated from cholera patients all
suggest that cholera will not be eradicated in the foreseeable future. As with other tropical diseases, there is growing concern that the combination of climate change,
anthropogenic disturbance of local environments, and
unintentional transport due to travel and trade will
expand the ranges of endemic strains, and consequently
create more focal points for cholera outbreaks. A more
complete understanding of the ecology of V. cholerae is
© The Ecological Society of America
KL Cottingham et al.
critical to the prediction and management of the associated disease. Of the suggestions for further research given
above, four topics are worthy of particular attention.
(1) V. cholerae provides an excellent model organism for
probing the function of heterotrophic bacteria in natural
ecosystems. Traditionally, microbial ecology has treated
bacteria as a “black box”, by necessity ignoring the identity and behavior of individual taxa (Leff and Lemke
1998). However, recent developments in molecular,
genetic, and genomic tools make it possible to follow particular species and to evaluate their role from the population, community, and ecosystem perspectives (Jackson et
al. 2002). V. cholerae is a well-studied pathogen that has
been extensively characterized (Faruque et al. 1998; Reidl
and Klose 2002), providing a wealth of information that
can be exploited for ecological studies. A number of interesting questions remain unanswered. How does the productivity of this model organism vary in free-living versus
attached states? How do productivity and population
dynamics, including biofilm development, change over
time once V. cholerae is attached to a host? Do these
dynamics vary on different hosts? How does bacterivory
affect population dynamics and ecosystem functioning?
What environmental signals cue entry into and out of a
VBNC state?
(2) The dual habitats and complex life history of
V. cholerae, when combined with the availability of a fully
sequenced genome (Heidelberg et al. 2000), make it an
excellent model for exploring the genetic basis of bacterial
behavior. Microarray technology, which allows the simultaneous quantification of the expression of each gene
(Gibson 2002), should be a particularly valuable tool.
How does gene expression differ in aquatic environments
as opposed to human hosts? What genes are involved in
attachment and the VBNC state? Are the same genes
involved in attachment to human hosts as to plankton?
What, if anything, do genes on the VPI and CTX- do in
aquatic environments? What are the correlations between
infectivity to humans and how the bacterium behaves in
aquatic environments? Recent work with other pathogenic bacteria indicates that virulence is linked to environmental performance (Hogan and Kolter 2002).
(3) Many gaps remain in our understanding of
V. cholerae’s behavior in aquatic ecosystems. For example,
how do the VBNC state, attachment, and vulnerability to
bacterivores vary across the salinity gradient from freshwater to estuarine to marine systems? How do population
dynamics differ when V. cholerae is free-living and when it
is attached? Does V. cholerae form biofilms on living hosts
or detrital aggregates? Does biofilm formation change the
tendency to go into a VBNC state or to be pathogenic to
humans? Better natural history information, in conjunction with experimental ecology and genetic research,
should improve the management of V. cholerae populations in nature.
(4) The interactions between bacterial genetics and the
ecology and evolutionary biology of V. cholerae are also
© The Ecological Society of America
Ecology and microbiology of Vibrio cholerae
worthy of attention, particularly as regards the emergence
of new pathogenic strains. We currently know little about
the ecological and evolutionary success of different strains
of V. cholerae, although there is some evidence for important ecological and clinical differences (Chiavelli et al.
2001; Longini et al. 2002). For example, what are the
adaptive advantages of attachment and the VBNC state?
Do V. cholerae O1 classical, O1 El Tor, and O139 show the
same tendencies to attach to hosts? Do all strains have the
ability to enter the VBNC state? Are all strains still infective while in the VBNC state? Are there differences in
grazing susceptibility? Does the presence of pathogenicity
genes, including the VPI and CTX-, alter V. cholerae’s
ability to survive and reproduce in aquatic environments?
How does V. cholerae evolve when introduced into new
habitats? Answers to these questions will improve our
understanding of how the human and aquatic habitats of
V. cholerae are linked, and will increase the likelihood of
developing effective control strategies.
Acknowledgments
We thank Anwar Huq, Siraj Islam, Eric Espelund, Huda
Khan, Jon Cole, and George O’Toole for their collaboration and insights. Julia Butzler and Jay Lennon provided
constructive reviews of earlier drafts of the manuscript.
Our work on the ecology of cholera is supported by the
Dartmouth College Center for Environmental Health
Sciences and a NSF Genome-Enabled Biocomplexity
grant (GEO 0120677).
References
Azam F, Smith DC, Steward GF, and Hagstrom A. 1994.
Bacteria–organic-matter coupling and its significance for
oceanic carbon cycling. Microbial Ecol 28: 167–79.
Boyd EF and Waldor MK. 2002. Evolutionary and functional
analyses of variants of the toxin-coregulated pilus protein TcpA
from toxigenic Vibrio cholerae non-O1/non-O139 serogroup
isolates. Microbiology 148: 1655–66.
Chiavelli DA, Marsh JW, and Taylor RK. 2001. The mannose-sensitive hemagglutinin of Vibrio cholerae promotes adherence to
zooplankton. Appl Environ Microb 67: 3220–25.
Cole JJ. 1999. Aquatic microbiology for ecosystem scientists: new
and recycled paradigms in ecological microbiology. Ecosystems
2: 215–25.
Colwell RR. 1996. Global climate and infectious disease: the
cholera paradigm. Science 274: 2025–31.
Colwell RR, Brayton P, Herrington D, et al. 1996. Viable but nonculturable Vibrio cholerae O1 revert to a cultivable state in the
human intestine. World J Microb Biot 12: 28–31.
Cotner JB and Biddanda BA. 2002. Small players, large role:
microbial influence on biogeochemical processes in pelagic
aquatic ecosystems. Ecosystems 5: 105–21.
Davey ME and O’Toole GA. 2000. Microbial biofilms: from ecology to molecular genetics. Microbiol Mol Biol R 64: 847–67.
Faruque SM, Albert MJ, and Mekalanos JJ. 1998. Epidemiology,
genetics, and ecology of toxigenic Vibrio cholerae. Microbiol Mol
Biol R 62: 1301–14.
Faruque SM and Nair GB. 2002. Molecular ecology of toxigenic
Vibrio cholerae. Microbiol Immunol 46: 59–66.
Franco AA et al. 1997. Cholera in Lima, Peru, correlates with prior
www.frontiersinecology.org
85
Ecology and microbiology of Vibrio cholerae
86
isolation of Vibrio cholerae from the environment. Am J
Epidemiol 146: 1067–75.
Gibson G. 2002. Microarrays in ecology and evolution: a preview.
Mol Ecol 11: 17–24.
Grossart HP and Simon M. 1998. Bacterial colonization and
microbial decomposition of limnetic organic aggregates (lake
snow). Aquat Microb Ecol 15: 127–40.
Harvell CD, Mitchell CE, Ward JR, et al. 2002. Climate warming
and disease risks for terrestrial and marine biota. Science 296:
2158–62.
Haugo AJ and Watnick PI. 2002. Vibrio cholerae CytR is a repressor
of biofilm development. Mol Microbiol 45: 471–83.
Heidelberg JF et al. 2002. DNA sequence of both chromosomes of
the cholera pathogen Vibrio cholerae. Nature 406: 477–86.
Hogan DA and Kolter R. 2002. Pseudomonas–Candida interactions:
an ecological role for virulence factors. Science 296: 2229–32.
Hood MA and Winter PA. 1997. Attachment of Vibrio cholerae
under various environmental conditions and to selected substrates. FEMS Microbiol Ecol 22: 215–23.
Huq A, Colwell RR, Rahman R, et al. 1990. Detection of Vibrio
cholerae O1 in the aquatic environment by fluorescent-monoclonal antibody and culture methods. Appl Environ Microb 56:
2370–73.
Huq A, Rivera ING, and Colwell RR. 2000. Epidemiological significance of viable but nonculturable microorganisms. In:
Colwell RR and Grimes DJ (Eds). Nonculturable microorganisms
in the environment. Washington, DC: American Society of
Microbiology Press.
Huq A, Small E, West P, and Colwell RR. 1984a. The role of
planktonic copepods in the survival and multiplication of
Vibrio cholerae in the environment. In: Colwell RR (Ed). Vibrios
in the environment. New York, NY: John Wiley & Sons.
Huq A, West PA, Small EB, Huq MI, and Colwell RR. 1984b.
Influence of water temperature, salinity, and pH on survival
and growth of toxigenic Vibrio cholerae serovar O1 associated
with live copepods in laboratory microcosms. Appl Environ
Microb 48: 420–24.
Islam MS, Drasar BS, Albert MJ, et al. 1997. Toxigenic Vibrio
cholerae in the environment: a minireview. Trop Dis Bull 94:
r1–11.
Islam MS, Drasar BS, and Sack RB. 1993. The aquatic environment as a reservoir of Vibrio cholerae: a review. J Diarrhoeal Dis
Res 11: 197–206.
Islam MS, Drasar BS, and Sack RB. 1994. The aquatic flora and
fauna as reservoirs of Vibrio cholerae: a review. J Diarrhoeal Dis
Res 12: 87–96.
Islam MS et al. 1999. Association of Vibrio cholerae O1 with the
cyanobacterium, Anabaena sp., elucidated by polymerase chain
reaction and transmission electron microscopy. Trans Roy Soc
Trop Med H 93: 36–40.
Jackson RB, Linder CR, Lynch M, et al. 2002. Linking molecular
insight and ecological research. Trends Ecol Evol 17: 409–14.
Jürgens K and Matz C. 2002. Predation as a shaping force for the
phenotypic and genotypic composition of planktonic bacteria.
Anton Leeuw Int J G 81: 413–34.
Kell DB, Kaprelyants AS, Weichart DH, et al. 1998. Viability and
activity in readily culturable bacteria: a review and discussion
of the practical issues. Anton Leeuw Int J G 73: 169–87.
Langenheder S and Jürgens K. 2001. Regulation of bacterial bio-
www.frontiersinecology.org
KL Cottingham et al.
mass and community structure by metazoan and protozoan predation. Limnol Oceanogr 46: 121–34.
Leff LG and Lemke MJ. 1998. Ecology of aquatic bacterial populations: lessons from applied microbiology. J N Am Benthol Soc
17: 261–71.
Lobitz B, Beck L, Huq A, et al. 2000. Climate and infectious disease: use of remote sensing for detection of Vibrio cholerae by
indirect measurement. P Natl Acad Sci USA 97: 1438–43.
Longini IM, Yunus M, Zaman K, et al. 2002. Epidemic and endemic
cholera trends over a 33-year period in Bangladesh. J Infect Dis
186: 246–51.
McCarthy SA. 1996. Effects of temperature and salinity on survival
of toxigenic Vibrio cholerae 01 in seawater. Microbial Ecol 31:
167–75.
McDougald D, Rice SA, Weichart D, and Kjelleberg S. 1998.
Nonculturability: adaptation or debilitation? FEMS Microbiol
Ecol 25: 1–9.
Merrell DS, Butler SM, Qadri F, et al. 2002. Host-induced epidemic
spread of the cholera bacterium. Nature 417: 642–45.
Mintz ED, Popovic T, and Blake PA. 1994. Transmission of Vibrio
cholerae O1. In: Wachsmuth IK, Blake PA, and Olsvik Ø (Eds).
Vibrio cholerae and cholera: molecular to global perspectives.
Washington, DC: American Society for Microbiology.
O’Toole G, Kaplan HB, and Kolter R. 2000. Biofilm formation as
microbial development. Annu Rev Microbiol 54: 49–79.
Pascual M, Bouma MJ, and Dobson AP. 2002. Cholera and climate:
revisiting the quantitative evidence. Microbes Infect 4: 237–45.
Pascual M, Rodo X, Ellner SP, et al. 2000. Cholera dynamics and El
Niño-Southern Oscillation. Science 289: 1766–69.
Patz JA and Khaliq M. 2002. Global climate change and health:
challenges for future practitioners. MSJama 287: 2283–84.
Pernthaler J, Sattler B, Simek K, et al. 1996. Top-down effects on
the size–biomass distribution of a freshwater bacterioplankton
community. Aquat Microb Ecol 10: 255–63.
Reidl J and Klose KE. 2002. Vibrio cholerae and cholera: out of the
water and into the host. FEMS Microbiol Rev 26: 125–39.
Ruiz GM, Rawlings TK, Dobbs FC, et al. 2000. Global spread of
microorganisms by ships. Nature 408: 49–50.
Tamplin ML, Gauzens AL, Huq A, et al. 1990. Attachment of
Vibrio cholerae serogroup O1 to zooplankton and phytoplankton
of Bangladesh waters. Appl Environ Microb 56: 1977–80.
Tauxe R, Seminario L, Tapia R, and Libel M. 1994. The Latin
American epidemic. In: Wachsmuth IK, Blake PA, and Olsvik
Ø (Eds). Vibrio cholerae and cholera: molecular to global perspectives. Washington, DC: American Society for Microbiology.
Theron J and Cloete TE. 2002. Emerging waterborne infections:
contributing factors, agents, and detection tools. Crit Rev
Microbiol 28: 1–26.
Threlkeld ST, Chiavelli DA, and Willey RL. 1993. The organization of zooplankton epibiont communities. Trends Ecol Evol 8:
317–21.
Wai SN, Moriya T, Kondo K, et al. 1996. Resuscitation of Vibrio
cholerae O1 strain tsi4 from a viable but nonculturable state by
heat shock. FEMS Microbiol Lett 136: 187–91.
Yildiz FH and Schoolnik GK. 1999. Vibrio cholerae O1 El Tor: identification of a gene cluster required for the rugose colony type,
exopolysaccharide production, chlorine resistance, and biofilm
formation. P Natl Acad Sci USA 96: 4028–33.
© The Ecological Society of America