Download Plant Pathogenic Bacteria

Plant
Pathogenic
Bacteria
Edited by
Solke H. De Boer
Kluwer Academic Publishers
extended to environmental applications. For example, Azospirillum s
can enhance the bioremediation of wastewater by microalgae by incr
algal prolíferaüon and metabolism. Azospirillum species may improv
reforestation of marine mangrove trees, thereby enhancing fisheries
tropical coasts and may prevent desert soil erosión and promote abatem
dust pollution by assisting in the growth of cactus species. The foll
minireview discusses these applications, and shows future potential av
for Azospirillum as an environmentally friendly microorganism.
Wastewater bioremediation
Microalgae have many uses, including water bioremediation. For suc
;ít ^íb "Ususííry iiesirdtíie 'to estáriiisn'iarge populations oí microalgae in a
environments. One means of increasing microalgal populations may
inocúlate them with PGPBs. A candidate microorganism for coinocu
with microalgae is Azospirillum bmsilense (strain Cd), a known plant g
promoting bacterium. To improve the growth, metabolism, and remo
nitrogen and phosphorus by the freshwater microalga Chlorella vulgaris
2714), an important organism often used in wastewater treatment, C. v
was inoculated with A. brasilense. The two microorganisms were kept i
proximity in the liquid médium essential for C. vulgaris by coimmobil
in alginate beads and were cocultivated under controlled conditions s
for both, in batch cultures and in continuous flow cultures in a chem
Alginate beads of various forms and shapes are convenient inoculant
for use in numerous industrial, environmental, and agricultural applicat
Coimmobilization of the freshwater microalga C. vulgaris and A. bra
in small alginate beads resulted in significant increased growth
microalga. Dry and fresh weight, total number of cells, size of the mic
clusters (colonies) within the bead, number of microalgal cells per clust
the levéis of microalgal pigments significantly increased. Ligh
transmission electrón microscopy revealed that both microorg
colonized the same cavities inside the beads, though the microalgae ten
concéntrate in the more aerated periphery, and the bacteria coloniz
S.H. De Boer (ed.), Plant Palhogenic Bacteria, 68-74.
© 2001 Kluwer Academic Publishers. Primea in the Netherlands.
s, A., Bethlenfalvay, G.J.,
imental Microbiology, The
z, B.C.S., 23000, MÉXICO,
I2L 3G1 GANADA (BRG).
gemís Azospirillum are
s. In addition to their
mtial benefits can be
e, Azospirillum species
icroalgae by increasing
¡cies may improve the
lancing fisheries along
i promote abatement of
species. The following
iture poíential a ve núes
'ganism.
lediation. For such use,
f microalgae in aquatic
Dopulations may be to
lism for coinoculation
a known plant growtholism, and removal of
hlorella vulgaris (UTEX
r treatment, C. vulgaris
isms were kept in cióse
is by coimmobilization
led conditions suitable
iltures in a chemostat.
lient inoculant carriers
cultural applications.
ígaris and A. brasilense
reased growth of the
, size of the microalgal
al cells per cluster, and
increased. Light and
both microorganisms
.e microalgae tended to
bacteria colonized the
culture prior to irnmobilization of microorganisms
imitated the effect of A brasilense.
Coimmobilization of C. vulgaris UTEX 395 a
brasilense resulted in significant changes in the m
and pigment content. The size of C. sorokiniana c
the populaüon within the beads significantly increa
UTEX 395 cells grew larger but their number did
vulgaris UTEX 2714, the pigment content of the m
increased as a result of coimmobilization.
The ability of the coimmobilized culture to cl
ammonium and phosphorus from the water) wa
cultures and in step cultures where the wastewa
hours. In continuous cultures, only modérate levé
in step cultures almost all of the ammonium
consecutive 48 hour cycles, the bioremediation sy
ammonium removal efficiency decreased. In co
reached after 3 cycles with immobilized microal
ammonium removal was reduced.
In another study, C. vulgaris (UTEX 2714) was
beads and coincubated with either A brasilense, or
bacterium Phyllobacterium myrsinacearum. The
microalga and the bacterial species were followe
microscopy for 10 days. Most of the small cavit
colonized by microcolonies of only one microo
bacterial species cocultured with the microalga.
and microalgal microcolonies merged to form large
cavities. At this stage, the effect of bacterial asso
differed depending on the bacterium present.
senescence phase in the presence of P. myrsinac
growth phase in the presence of A brasilense. Th
are commensal interactions between the micr
associative bacteria and that with time the ba
whether the outcome for the microalga is
multiplication.
The delibérate inoculation of Chlorella sp. with
reported prior to these studies, perhaps because of
two microorganisms. C. vulgaris is not known
beneficial bacteria, and Azospirillum sp, is rare
aquatic environments. These studies indicate that
microalga by the plant growth-promoting bacterium
of the microalga as a wastewater treatment age
coimmobilization of microalgae and plant growth
ecosystems are rain forests and coral reefs.
Despite their importance, mangroves face the sanie destm
deforestation as the rain forests. To aid mangrove reforestation, it has
proposed that seedlings are inoculated with plant growth-promoting ba
(PGPB), a practice that has been successful in agriculture and tem
forestry. Mangrove seedlings usually grow better after inoculation wi
diazotrophic filamentous cyanobacteria Microcoleus chthonoplastes (3).
on this observatioru it was reasimed that tcumgTOve seadiings, wÁgb
benefit from inoculation with plant growth-p'romoting bacteria. Ni
fixation by inoculants in mangrove sediments, in the rhizosphere
associated with aerial roots may provide the nitrogen necessary for
growth, and phosphate-solubilizing microorganisms may supply plañís
sufficient amount of phosphorus.
Inoculation of axenic black mangrove seedlings in seawater for eigh
with either the terrestrial halotolerant plant growth-promoting bacteri
halopraeferens or with A. brasilense produced heavy colonization of th
surface. The colonization pattern was different for the two strain
halopraeferens was present mainly as single cells embedded in a thick s
whereas A. brasilense produced primarily microaggregates. A brasilens
were anchored to the root surfaces and to each other by a network of f
material. Both bacterial strains survived in seawater (approx. 104 cfu/m
more than 30 days, and colonized mangrove roots at a high density. W
halopraeferens was a better root surface colonizer, A brasilense was bett
to popúlate the entire root (surface and inside) (9),
Plant growth-promoting bacteria native to mangrove ecosystems are
unknown. Recently, several bacteria isolated from mangroves promot
growth of Salicornia bigelovü, a poteníial oilseed crop that grows in se
s feeding, spawning, and
id ecologically important
vegetate themselves after
rcutting, mangroves rarely
;onsidered to be nutrienttrogen and phosphorous.
s flourish with no obvious
iré microorganisms are the
ve productivity. Probably
are one of the three most
er two highly productive
the same destructive
reforestation, it has been
jrowth-promoting bacteria
.griculture and températe
ifter inoculation with the
chthonoplastes (3). Based
ave seedlings might also
tioting bacteria. Nitrogen
in the rhizosphere, and
ogen necessary for plant
may supply plants with a
in seawater for eight days
i-promoting bacterium A.
y colonization of the root
For the two strains. A.
ibedded in a thick sheath,
•egates. A brasilense cells
r by a network of fibrillar
r (approx. 104 cfu/mL) for
t a high density. While A
brasilense was better able
>ve ecosystems are almost
mangroves promoted the
:>p that grows in semiarid
yet been explored. Two potential mangro
rhizosphere of semiarid zone mangroves, wer
culture médium or in seawater; the slo
Phyllobacterium sp. and the fast-growing p
Baciüus licheniformis. N2-fixation and phosph
in the mixed culture compared to monocult
that when the two bacterial species were grow
one morphotype colony containing both spec
they grew separately. Though enhanced
observad in mixed cultures growing in se
bacterial species increased at the same rate as
Inoculation of black mangrove propagules
bacterial cultures showed some advan
monocultures; more leaves developed an
incorporated in the leaves, however, the tota
illustrates that interactions between microo
mangroves can influence plant development
applying plant growth-promoting bacteria. T
long-term study designed to assess the fea
marine plant growth-promoting bacteria for
for environmental purposes.
Desert reforestation
When naturally vegetated deserts are
agricultural land that is later abandon
"desertification"), or to build urban neigh
nothing remains to prevent the topsoil from b
is severe soil erosión and subsequent dust po
significantly increases chronic respiratory i
been increasing throughout the developing
predominant in the semiarid áreas of northe
northwestern México quickly become a bar
annual plants. These áreas cannot reforest n
because nurse trees (which provide a canopy
establishment of cactus seedlings have been re
plants tested had VAM associations but the extent of root colonization by t
mycorrhizal fungí varied widely (<10 to > 70%). Cactus species with lo
VAM colonization thrived mainly near nurse trees. Of the nine species of tre
and arborescent shrubs in the área, the mature (>20 year) nurse legum
Prosopis artículata (mesquite) and Olneya tesota (ironwood) supported t
largest number of understory plants. The VAM inoculum potential under t
mesquite canopy and in áreas devoid of plants was similar (1), however t
propagule density of VAM under the canopy was 7-fold higher. These stud
show that VAM fungí help to stabilize windborne soil that settles under de
plant canopies by formation of soil aggregation and enhance colonization
cactus seedlings (6).
Bacteria may also contribute to the revegetation of disturbed desert áre
Seedlings of the giant cardón cactus (Pachycereus pringlei) were inoculat
with A. brasilense in pot cultures containing different soils ranging from ri
soil from under the mesquite canopy to poor soil from barren áreas. In ri
soil, A. brasilense had no effect on cardón cactus development. However,
poor soil, inoculation increased dry vegetativa mass by 60% and root length
over 100%. The effect was not caused by Nz fixation by the bacterium becau
acetylene reduction acíivity was not detected in íhe roots (5).
Survival and development of cactus transplants in urban, disturbed áreas
the desert near La Paz, Baja California Sur, México was monitored. You
plants of three species of tree-shaped cacti (Pachycereus pringlei, Stenocer
thurberí, and Lophocereus schottíi) were inoculated with íhe plant grow
promoting bacterium vi. brasilense ín an eroded área (a dirt road). Inoculat
plants had a higher survíval rate and developed more rapidly th
uninoculated control plants during a 3.5-year period after transplantation. S
erosión in the inoculated experimental área diminished. Small, but significa
soil accumulation was associaíed with íhe growíh of cactus small roots in t
wind-deposited dust. The upward growth of small roots into the deposit
it in urban áreas, however
• ío develop after being
0 eroded urban soil. Cacti
>rganisms during planting
températe reforestation.
•hizal fungí may aid the
osion and dust pollution.
igi may help stabilize
ired dust) under mesquite
ie understory. The VAM
man-made removal of the
le Sonoran desert near La
1 46 species of perennial
if root colonization by the
Cactus species with low
)f the nine species of trees
>20 year) nurse legumes
ironwood) supported the
;ulum potential under the
i similar (1), however the
oíd higher. These studies
il that settles under dense
enhance colonization by
of disturbed desert áreas.
pringlei) were inoculated
nt soils ranging from rich
rom barren áreas. In rich
levelopment. However, in
3y 60% and root length by
by the bacterium because
oots (5).
i urban, disturbed áreas of
:o was monitored. Young
;reus pringlei, Stenocereus
i with the plant growtha (a dirt road). Inoculated
ped more rapidly than
after transplantation. Soil
ted. Small, but significant,
f cactus small roots in the
roots into the deposited
brasilense survived well in the rhizospheres of mese
not in root-free soil (4).
These studies demónstrate that (i) the natural rev
desert can be mimicked by revegetation programs, an
cacti with fungi or bacteria can enhance their establish
and can thereby stabilize soil.
Acknowledgements
This study is dedicated to the memory of the late
Israel. We thank Dr. Ellis Glazier for editing the Englis
Cheryl Paiten for critical reading and English s
supported by Consejo Nacional de Ciencia y Tecnolog
contraéis # 26262-B and # 28362-B, and by the Basha
References
1. Bashan, Y., Davis, E. A., Carrillo, A. and Linderman
of VA mycorrhizal noculum potential in relation
cactus seedlings under mesquite nurse-trees in th
SoilEcol. 14:165-176.
2. Bashan, Y., Moreno, M., and Troyo, E. 2000. G
seawater-irrigated oilseed halophyte Salicornia b
mangrove rhizosphere bacteria and halotolerant
Fértil. Soils 31: [in press)
3. Bashan, Y., Puente, M.E., Myrold, D.D. and To
transfer of fixed nitrogen from diazotrophic filam
black mangrove seedlings. FEMS Microbiol. Ecol.
4. Bashan, Y. Rojas, A. and Puente, M.E. 1999. Imp
development of three cacti species inoculated wit
transplanted into disturbed urban desert soil. Ca
451
5. Carrillo-Garcia, A., Bashan, Y., Diaz-Rivera, E.,
2000. Effects of resource - island soils, competiti
Azospirillum on survival and growth of Pachyc
cactus of the Sonoran Desert. Restor. Ecol. 8: 65-7
6. Carrillo-Garcia, A., León de la Luz, J.-L., Bashan, Y
1999. Nurse plants, mycorrhizae, and plant estab
área of the Sonoran desert. Restor. Ecol. 7: 321-335
7. González, L.E., and Bashan, Y. 2000. Increased
Chlorella vulgaris when coimmobilized and cocu
with the plant growth-promoting bacterium Azosp
Environ. Microbiol. 66: 1527-1531