Download Bacterial culture Microbiological cultures can be grown in petri

Advance Systemic Bacteriology – II
1. Briefly discuss the impact of pH on microbial growth.
Bacterial growth is the division of one bacterium into two daughter cells in a process called binary
fission. Providing no mutational event occurs the resulting daughter cells are genetically identical to the
original cell. Hence, "local doubling" of the bacterial population occurs. Both daughter cells from the
division do not necessarily survive. However, if the number surviving exceeds unity on average, the
bacterial population undergoes exponential growth. The measurement of an exponential bacterial growth
curve in batch culture was traditionally a part of the training of all microbiologists; the basic means
requires bacterial enumeration (cell counting) by direct and individual (microscopic, flow cytometry[1]),
direct and bulk (biomass), indirect and individual (colony counting), or indirect and bulk (most probable
number, turbidity, nutrient uptake) methods. Models reconcile theory with the measurements.[2]
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[edit]Phases
In autecological studies, bacterial growth in batch culture can be modeled with four different phases: lag
phase (A), exponential or log phase (B),stationary phase (C), and death phase (D). IN the book "black"
the bacterial growth phase classified 07 stages like-(A)lag phase (B)early log phase (C) log/exponential
Phase (D)Early Stationery phase (E)stationary phase (f) Early Death phase (G)Death phase..
1. During lag phase, bacteria adapt themselves to growth conditions. It is the period where the
individual bacteria are maturing and not yet able to divide. During the lag phase of the bacterial
growth cycle, synthesis of RNA, enzymes and other molecules occurs.
2. Exponential phase (sometimes called the log phase or the logarithmic phase) is a period
characterized by cell doubling.[3] The number of new bacteria appearing per unit time is
proportional to the present population. If growth is not limited, doubling will continue at a constant
rate so both the number of cells and the rate of population increase doubles with each
consecutive time period. For this type of exponential growth, plotting the natural logarithm of cell
number against time produces a straight line. The slope of this line is the specific growth rate of
the organism, which is a measure of the number of divisions per cell per unit time. [3] The actual
rate of this growth (i.e. the slope of the line in the figure) depends upon the growth conditions,
which affect the frequency of cell division events and the probability of both daughter cells
surviving. Under controlled conditions, cyanobacteria can double their population four times a
day.[4] Exponential growth cannot continue indefinitely, however, because the medium is soon
depleted of nutrients and enriched with wastes.
3. During stationary phase, the growth rate slows as a result of nutrient depletion and accumulation
of toxic products. This phase is reached as the bacteria begin to exhaust the resources that are
available to them. This phase is a constant value as the rate of bacterial growth is equal to the
rate of bacterial death.
4. At death phase, bacteria run out of nutrients and die.
This basic batch culture growth model draws out and emphasizes aspects of bacterial growth which may
differ from the growth of macrofauna. It emphasizes clonality, asexual binary division, the short
development time relative to replication itself, the seemingly low death rate, the need to move from a
dormant state to a reproductive state or to condition the media, and finally, the tendency of lab adapted
strains to exhaust their nutrients.
2. Explain the principle and working mechanism of an electron microscope.
An electron microscope is a type of microscope that uses a beam of electrons to illuminate the
specimen and produce a magnified image. Electron microscopes (EM) have a greater resolving
power than a light-powered optical microscope, because electrons have wavelengths about 100,000
times shorter than visible light (photons), and can achieve better than
50 pm resolution[1] and magnifications of up to about 10,000,000x, whereas ordinary, non-confocal light
microscopes are limited by diffraction to about 200 nm resolution and useful magnifications below 2000x.
The electron microscope uses electrostatic and electromagnetic "lenses" to control the electron beam and
focus it to form an image. These lenses are analogous to, but different from the glass lenses of an optical
microscope that form a magnified image by focusing light on or through the specimen. Electron
microscopes are used to observe a wide range of biological and inorganic specimens
including microorganisms, cells, large molecules, biopsy samples,metals, and crystals. Industrially, the
electron microscope is often used for quality control and failure analysis.
The electron microscope was invented and patented by Hungarian physicist Leó Szilárd who declined to
construct it.[2] Instead, German physicist Ernst Ruska and electrical engineer Max Knoll constructed
the prototype electron microscope in 1931, capable of four-hundred-power magnification; the apparatus
was a practical application of the principles of electron microscopy. [3] Two years later, in 1933, Ruska built
an electron microscope that exceeded the resolution attainable with an optical (lens)
microscope.[3] Moreover, Reinhold Rudenberg, the scientific director of Siemens-Schuckertwerke,
obtained the patent for the electron microscope in May 1931. Family illness compelled the electrical
engineer to devise an electrostatic microscope, because he wanted to make visible the poliomyelitis virus.
In 1932, Ernst Lubcke of Siemens & Halske built and obtained images from a prototype electron
microscope, applying concepts described in the Rudenberg patent applications. [4] Five years later (1937),
the firm financed the work of Ernst Ruska and Bodo von Borries, and employed Helmut Ruska (Ernst’s
brother) to develop applications for the microscope, especially with biologic specimens. [3][5] Also in
1937, Manfred von Ardenne pioneered the scanning electron microscope.[6] The first practical electron
microscope was constructed in 1938, at the University of Toronto, by Eli Franklin Burton and students
Cecil Hall,James Hillier, and Albert Prebus; and Siemens produced the first commercial transmission
electron microscope (TEM) in 1939.[7] Although contemporary electron microscopes are capable of two
million-power magnification, as scientific instruments, they remain based upon Ruska’s prototype.
3. Describe sexual reproduction in fungi.
A fungus (
/ˈfʌŋɡəs/; plural: fungi[3] or funguses[4]) is a member of a large group
of eukaryotic organisms that includes microorganisms such asyeasts and molds (British English: moulds),
as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is
separate from plants, animals, and bacteria. One major difference is that fungal cells have cell walls that
contain chitin, unlike the cell walls of plants, which contain cellulose. These and other differences show
that the fungi form a single group of related organisms, named the Eumycota (true fungi or Eumycetes),
that share a common ancestor (a monophyletic group). This fungal group is distinct from the structurally
similar myxomycetes(slime molds) and oomycetes (water molds).
The discipline of biology devoted to the study of fungi is known as mycology, which is often regarded as a
branch of botany, even though genetic studies have shown that fungi are more closely related to animals
than to plants.
Abundant worldwide, most fungi are inconspicuous because of the small size of their structures, and
their cryptic lifestyles in soil, on dead matter, and as symbionts of plants, animals, or other fungi. They
may become noticeable when fruiting, either as mushrooms or molds. Fungi perform an essential role in
the decomposition of organic matter and have fundamental roles in nutrient cycling and exchange. They
have long been used as a direct source of food, such as mushrooms and truffles, as a leavening agent for
bread, and in fermentation of various food products, such as wine,beer, and soy sauce. Since the 1940s,
fungi have been used for the production of antibiotics, and, more recently, various enzymes produced by
fungi are used industrially and in detergents. Fungi are also used as biological pesticides to control
weeds, plant diseases and insect pests. Many species produce bioactive compounds called mycotoxins,
such as alkaloids and polyketides, that are toxic to animals including humans. The fruiting structures of a
few species contain psychotropic compounds and are consumed recreationally or in traditional spiritual
ceremonies. Fungi can break down manufactured materials and buildings, and become
significant pathogens of humans and other animals. Losses of crops due to fungal diseases (e.g. rice
blast disease) or food spoilage can have a large impact on human food supplies and local economies.
The fungus kingdom encompasses an enormous diversity of taxa with varied ecologies, life
cycle strategies, and morphologies ranging from single-celled aquatic chytrids to large mushrooms.
However, little is known of the true biodiversity of Kingdom Fungi, which has been estimated at around
1.5 million species, with about 5% of these having been formally classified.[citation needed] Ever since the
pioneering 18th and 19th centurytaxonomical works of Carl Linnaeus, Christian Hendrik Persoon,
and Elias Magnus Fries, fungi have been classified according to their morphology (e.g., characteristics
such as spore color or microscopic features) or physiology. Advances in molecular genetics have opened
the way for DNA analysis to be incorporated into taxonomy, which has sometimes challenged the
historical groupings based on morphology and other traits.Phylogenetic studies published in the last
decade have helped reshape the classification of Kingdom Fungi, which is divided into one subkingdom,
seven phyla, and ten subphyla.
4. Write a detailed account on different types of microbial culture media.
A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by
letting them reproduce in predetermined culture media under controlled laboratory conditions. Microbial
cultures are used to determine the type of organism, its abundance in the sample being tested, or both. It
is one of the primary diagnostic methods of microbiology and used as a tool to determine the cause
of infectious disease by letting the agent multiply in a predetermined medium. For example, a throat
culture is taken by scraping the lining of tissue in the back of the throat and blotting the sample into a
medium to be able to screen for harmful microorganisms, such as Streptococcus pyogenes, the causative
agent of strep throat.[1] Furthermore, the term culture is more generally used informally to refer to
"selectively growing" a specific kind of microorganism in the lab.
Microbial cultures are foundational and basic diagnostic methods used extensively as a research tool
in molecular biology. It is often essential to isolate a pure culture of microorganisms. A pure (or axenic)
culture is a population of cells or multicellular organisms growing in the absence of other species or types.
A pure culture may originate from a single cell or single organism, in which case the cells are
genetic clones of one another.
For the purpose of gelling the microbial culture, the medium of agarose gel (agar) is used. Agar is a
gelatinous substance derived from seaweed. A cheap substitute for agar is guar gum, which can be used
for the isolation and maintenance of thermophiles.
Bacterial culture
Microbiological cultures can be grown in petri dishes of differing sizes that have a thin layer of agar-based
growth medium. Once the growth medium in the petri dish is inoculated with the desired bacteria, the
plates are incubated at the best temperature for the growing of the selected bacteria (for example, usually
at 37 degrees Celsius for cultures from humans or animals, or lower for environmental cultures).
Another method of bacterial culture is liquid culture, in which the desired bacteria are suspended in liquid
broth, a nutrient medium. These are ideal for preparation of an antimicrobial assay. The experimenter
would inoculate liquid broth with bacteria and let it grow overnight (they may use a shaker for uniform
growth). Then they would take aliquots of the sample to test for the antimicrobial activity of a specific drug
or protein (antimicrobial peptides).
5. Explain the control of microorganisms using antibiotics.
6. Describe generalized transduction.
Transduction is the process by which DNA is transferred from one bacterium to another by a virus.[1] It
also refers to the process whereby foreign DNA is introduced into another cell via a viral vector.
Transduction does not require cell-to-cell contact (which occurs in conjugation), and it is DNAase resistant
(transformation is susceptible to DNAase). Transduction is a common tool used by molecular biologists to
stably introduce a foreign gene into a host cell's genome.
When bacteriophages (viruses that infect bacteria) infect a bacterial cell, their normal mode of
reproduction is to harness thereplicational, transcriptional, and translation machinery of the host bacterial
cell to make numerous virions, or complete viral particles, including the viral DNA or RNA and the protein
coat.
Transduction and specialized transduction are especially important because they explain how antibiotic
drugs become ineffective due to the transfer of resistant genes between bacteria. In addition, hopes to
create medical method
Transduction as a method of transfer genetic material
The packaging of bacteriophage DNA has low fidelity and small pieces of bacterial DNA, together with the
bacteriophage genome, may become packaged into the bacteriophage genome. At the same time, some
phage genes are left behind in the bacterial chromosome.
There are generally three types of recombination events that can lead to this incorporation of bacterial
DNA into the viral DNA, leading to two modes of recombination.
[edit]Generalized
Transduction
Generalized transduction is the process by which any bacterial gene may be transferred to another
bacterium via a bacteriophage, and typically carries only bacterial DNA and no viral DNA. In essence, this
is the packaging of bacterial DNA into a viral envelope. This may occur in two main ways, recombination
and headful packaging.
If bacteriophages undertake the lytic cycle of infection upon entering a bacterium, the virus will take
control of the cell’s machinery for use in replicating its own viral DNA. If by chance bacterial chromosomal
DNA is inserted into the viral capsid which is usually used to encapsulate the viral DNA, the mistake will
lead to generalized transduction.
If the virus replicates using 'headful packaging', it attempts to fill the nucleocapsid with genetic material. If
the viral genome results in spare capacity, viral packaging mechanisms may incorporate bacterial genetic
material into the new virion.
The new virus capsule now loaded with part bacterial DNA continues to infect another bacterial cell. This
bacterial material may become recombined into another bacterium upon infection.
When the new DNA is inserted into this recipient cell it can fall to one of three fates
1. The DNA will be absorbed by the cell and be recycled for spare parts.
7. Write an account on chemotaxonamy.
8. Describe the structure and replication of plant rhabdovirus.