2. 1. Medical Microbiology
• Medical microbiology, deals with diseases of humans and
animals. Medical microbiologists identify the agents causing
infectious diseases and help plan measures for their control
and elimination. Frequently they are involved in tracking
down new, unidentified pathogens such as those causing
variant Creutzfeldt-Jakob disease (the human version of
"mad cow disease''), Hantavirus pulmonary syndrome, and
These microbiologists also study the ways microorganisms
cause disease.
3. • As described in section above our understanding of the role of
microbes in disease began to crystallize when we were able to isolate
them in pure culture.
• Today, clinical laboratory scientists, the microbiologists who work in
hospital and other clinical laboratories, use a variety of techniques to
provide information needed by physicians to diagnose infectious
disease. Increasingly, molecular genetics techniques are also being
used
4. 2. Public Health Microbiology
• Major epidemics have regularly affected human history. The 1918
influenza pandemics of particular note it killed more than 50 million
people in about a year. Public health microbiology is concerned with the
control and spread of such communicable diseases.
• Public health microbiologists and epidemiologists monitor the amount of
disease in populations. Based on their observations, they can detect
outbreaks and developing epidemics, and implement appropriate control
measures. They also conduct surveillance for new diseases as well as
bioterrorism events. Public health microbiologists working for local
governments monitor community food establishments and water supplies
to ensure they are safe and free from pathogens.
• To understand, treat, and control infectious disease, it is important to
understand how the immune system protects the body from pathogens;
this question is the concern of immunology.
5. 3. Immunology
• Immunology is one of the fastest growing areas in science.
Much of the growth began with the discovery of the human
immunodeficiency virus (HIV), which specifically targets cells
of the immune system. Immunology also deals with the
nature and treatment of allergies and auto immune diseases
such as rheumatoid arthritis.
6. 4. Ecology
• Microbial ecology is another important field in microbiology.
Microbial ecology developed when early microbiologists such as
Winogradsky and Beijerinck chose to investigate the ecological role of
microorganisms rather than their role in disease. Today, a variety of
approaches, including non-culture-based techniques, are used to
describe the vast diversity of microbes in terms of their morphology,
physiology, and relationships with organisms and the components of
their habitats. The importance of microbes in global and local cycling
of carbon, nitrogen, and sulfur is well documented; however, many
questions are still unanswered. Of particular interest is the role of
microbes in both the production and removal of greenhouse gases
such as carbon dioxide and methane.
7. • Microbial ecologists also are employing microorganisms in
bioremediation to reduce pollution. A new frontier in microbial
ecology is the study of the microbes normally associated with the
human body-so-called human microbiota.
• Scientists are currently trying to identify all members of the human
microbiota using molecular techniques that grew out of Woese's
pioneering work to establish the phylogeny of microbes.
8. 5. Industries
• Industrial microbiologists identify or genetically engineer microbes of
use to industrial processes, medicine, agriculture, and other
commercial enterprises. They also utilize techniques to improve
production by microbes and devise systems for culturing them and
isolating the products they make.
• The advances in medical microbiology, agricultural microbiology, food
and dairy microbiology, and industrial microbiology are in many ways
out growths of the labor of many microbiologists doing basic research
in areas such as microbial physiology, microbial genetics, molecular
biology, and bioinformatics.
9. • Microbes are metabolically diverse and can employ a wide variety of
energy sources, including organic matter, inorganic molecules (e.g.,
H2 and NH3), and sunlight. Microbial physiologists study many
aspects of the biology of microorganisms, including their metabolic
capabilities. They also study the synthesis of antibiotics and toxins,
the ways in which microorganisms survive harsh environmental
conditions, and the effects of chemical and physical agents on
microbial growth and survival. Microbial geneticists, molecular
biologists, and bioinformaticists study the nature of genetic
information and how it regulates the development and function of
cells and organisms. The bacteria E. coli and Bacillus subtilis, the yeast
Saccharomyces cerevisiae (baker's yeast), and bacterial viruses such
as T4 and lambda continue to be important model organisms used to
understand biological phenomena.
10. • Clearly, the future of microbiology is bright. Genomics in particular is
revolutionizing microbiology, as scientists are now beginning to
understand organisms as generall. How the genomes of microbes
evolve, the nature of host-pathogen interactions, the minimum set of
genes required for an organism to survive, and many more topics are
aggressively being examined by molecular and genomic analyses. This
is an exciting time to be a microbiologist.
11. 6. Agriculture
• Agricultural microbiology is a field related to both medical
microbiology and microbial ecology. Agricultural microbiology is
concerned with the impact of microorganisms on agriculture.
Microbes such as nitrogen-fixing bacteria play critical roles in the
nitrogen cycle and affect soil fertility. Other microbes live in the
digestive tracts of ruminants such as cattle and break down the plant
materials these animals ingest. There are also plant and animal
pathogens that have significant economic impact if not controlled.
12. • Furthermore, some pathogens of domestic animals also can
cause human disease. Agricultural microbiologists work on
methods to increase soil fertility and crop yields, study
rumen microorganisms in order to increase meat and milk
production, and try to combat plant and animal diseases.
Currently many agricultural microbiologists are studying the
use of bacterial and viral insect pathogens as substitutes for
chemical pesticides.
13. • Agricultural microbiology has contributed to the ready supply of high-
quality foods, as has the discipline of food and dairy microbiology.
Numerous foods are made using microorganisms.
• On the other hand, some microbes cause food spoilage or are
pathogens that are spread through food. Excellent examples of the
latter are the rare Escherichia coli 0104:H4, which in 2011 caused a
widespread outbreak of disease in Europe thought to have been
spread by bean sprouts, and also in 2011, contaminated ground
turkey was implicated in a Salmonella outbreak in the United States.
Food and dairy microbiologists explore the use of microbes in food
production. They also work top revent microbial spoilage of food and
the transmission of food- borne diseases. This involves monitoring the
food industry for the presence of pathogens.
14. • Increasingly, molecular methods are being used to detect pathogens
in meat and other foods. Food and dairy microbiologists also conduct
research on the use of microorganisms as nutrient sources for
livestock and humans. …Microbiology of food.
15. Agricultural Microbiology
• Agricultural Microbiology is a branch of microbiology dealing with
plant-associated microbes and plant and animal diseases. It also deals
with the microbiology of soil fertility, such as microbial degradation of
organic matter and soil nutrient transformations.
• Importance of soil microorganisms
• Involved in nutrient transformation process
• Decomposition of resistant components of plant and animal tissue
• Role in microbial antagonism
16. Microorganisms as bio fertilizers
• Bio fertilizers are seen as promising, sustainable alternatives
to harmful chemical fertilizers due to their ability to increase
yield and soil fertility through enhancing crop immunity and
development. When applied to the soil, plant, or seed these
bio fertilizers colonize the rhizosphere or interior of the plant
root. Once the microbial community is established, these
microorganisms can help to solubilize and break down
essential nutrients in the environment which would
otherwise be unavailable or difficult for the crop to
incorporate into biomass.
17. Nitrogen
• Nitrogen is an essential element needed for the creation of biomass
and is usually seen as a limiting nutrient in agricultural systems.
Though abundant in the atmosphere, the atmospheric form of
nitrogen cannot be utilized by plants and must be transformed into a
form that can be taken up directly by the plants; this problem is
solved by biological nitrogen fixers. Nitrogen fixing bacteria, also
known as diazotrophs, can be broken down into three groups: free-
living (ex. Azotobacter, Anabaena, and Clostridium) , symbiotic
(ex. Rhizobium and Trichodesmium) and associative symbiotic
(ex. Azospirillum).
18. • These organisms have the ability to fix atmospheric nitrogen to
bioavailable forms that can be taken up by plants and incorporated
into biomass. An important nitrogen fixing symbiosis is that
between Rhizobium and leguminous plants. Rhizobium have been
shown to contribute upwards of 300 kg N/ha/year in different
leguminous plants, and their application to agricultural crops has
been shown to increase crop height, seed germination, and nitrogen
content within the plant. The utilization of nitrogen fixing bacteria in
agriculture could help reduce the reliance on man-made nitrogen
fertilizers that are synthesized.
19. Phosphorus
• Phosphorus can be made available to plants via solubilization or
mobilization by bacteria or fungi. Under most soil conditions,
phosphorus is the least mobile nutrient in the environment and
therefore must be converted to solubilized forms in order to be
available for plant uptake. Phosphate solubilization is the process by
which organic acids are secreted into the environment, this lowers
the pH and dissolves phosphate bonds therefore leaving the
phosphate solubilized. Phosphate-solubilizing bacteria
(PBS) (ex. Bacillus subtilis and Bacillus circulans) are responsible for
upwards of 50% of microbial phosphate solubilization.
20. • In addition to the solubilized phosphate, PBS can also provide trace
elements such as iron and zinc which further enhance plant growth.
Fungi (ex. Aspergillus awamori and Penicillium spp.) also perform this
process, however their contribution is less than 1% of all activity.
• A 2019 study showed that when crops were inoculated
with Aspergillus niger , there was a significant increase fruit size and
yield compared with non-inoculated crops; when the crop was co-
inoculated with A. niger and the nitrogen fixing bacteria Azobacter,
the crop performance was better than with inoculation using only
one of the bio fertilizer and the crops that were not inoculated at all.
21. • Phosphorus mobilization is the process of transferring phosphorus to
the root from the soil; this process is carried out
via mycorrhiza (ex. Arbuscular mycorrhiza) . Arbuscular
mycorrhiza mobilize phosphate by penetrating and increasing the
surface area of the roots which helps to mobilize phosphorus into the
plant. Phosphate solubilizing and mobilizing microorganisms can
contribute upwards of 30–50 kg P2O5/ha which, in turn, has the
potential to increase crop yield by 10–20%.
22. They affect plant growth by Microbes:
• By decomposing root nodules.
• By removing nutrients from the plant.
• They impact normal photosynthetic functions.
• They can cause plant diseases like chlorosis and necrosis.
• They lead to a decrease in nutrient uptake and mobilization.
• They also lead to a decrease in the translocation of water and
nutrients through the vascular system.
23. What are pathogenic microorganisms for crops?
• On the other hand, pathogenic microorganisms present in agricultural soils
can have a harmful effect on the crop inducing:
• i) pathogenicity and disease,
• ii) resistance to crop control products,
• iii) poor soil health or reduced fertility,
• iv) poor crop health or poor yields, and lastly
• v) crop loss.
• Pathogenic microbes can be detrimental to crop yield, reduce food quality
and promote disease spread. These pathogens are often difficult to control
and to manage, once widespread. Pathogenic microorganisms include
fungi, oomycetes, bacteria and viruses. Some of these pathogenic
microorganisms will decompose root nodules, leaching nutrients from the
plant, reducing the efficiency of nutrient uptake and mobilization, and
further leading to nutrient deficiency and stunted plant growth.
24. • The presence of pathogens can also impact photosynthetic
functioning, causing chlorosis and necrosis of leaves and stems
resulting in a reduction in the translocation of water and nutrients
through the vascular system. This often occurs through the assistance
of toxins that colonize the host tissue; these toxins have a negative
impact on the host plant and are often host-specific. As a
consequence, this will stunt growth and lead to plant death if not
managed and treated. Other symptoms of pathogenic invasion
include blight, canker, distortion, leaf scorch or spot and gummosis.
25. • Examples of pathogenic microorganism
include Phytophthora, Fusarium, Verticillium, Pythium and Rhizoctonia.
There are over a 100 species of the pathogenic oomycete Phytophthora,
which is also known as the plant destroyer. This pathogenic microorganism
can be very damaging to many plants, particularly, ornamental and
horticultural crops. Phytophthora spores can survive in plant debris or soil
for many years and can infect all parts of the plant, but it usually attacks
the roots or stem base. Fusarium is a fungal genus that is widely
distributed in soil. Most species of Fusarium are harmless saprobes
(decomposers that feed on decaying organic matter), but some species can
have devastating impact on crops. For instance, they can cause Fusarium
stem canker, Fusarium root rot, Fusarium wilt in different type of crops,
and pathogenic Fusarium species are hardly manageable due to their
ability to survive for extended periods in the soil. Verticillium is a soil-borne
fungal disease, which causes widespread wilting of affected plants, it
pierces host roots to grow into the xylem of the plant, reducing water
transport and increasing toxin movement, leading to the death of plant
tissues. Pythium causes common crop diseases
26. • like root rot, often involving seed decay and seedling death. This
fungus will reduce root growth, overall plant growth, and lead to the
destruction of the hypocotyl (the stem of a germinating seed) and
main root system. This will eventually cause infected plants to wilt
and die. Lastly, fungal bacteria Rhizoctonia is responsible for many
commercially significant crop diseases, for example turf grass disease,
seedling damping, black scurf in potatoes, root rot and sheath blight.
