The document discusses nitrogen fixation, which is the process by which nitrogen in the atmosphere is converted into a form that can be used by living things. It then provides details about the general characteristics of bacteria, including that they are single-celled organisms without organelles, have a cell wall composed of peptidoglycan, can reproduce through binary fission, and can perform both aerobic and anaerobic respiration. Finally, it lists 13 biological importance of bacteria, such as their role in producing antibiotics, decomposing waste, and processing foods like cheese and yogurt.

1. Nitrogen Fixations
• Process by which nitrogen in the atmosphere
is converted into a form that can be used by
living things

2. All bacteria are Prokaryotes
General Characteristics of Bacteria
• All are single-cell organisms, rarely cluster as multicellular in
cyanobacteria
• No nucleus or other membrane-bound organelles
(mitochondria, chloroplasts)
• Metabolic reactions occur in folds of plasma membrane
• Cell wall (Functions as a protective barrier) is composed of
peptidoglycan found in most cells
• External layers may be present as capsule or slime layer
• Genome is DNA (single, circular chromosome without histones)
in “nucleoid”

3. • Flagella (whip-like structures) when present consist of
fibris of flagellin
• Pili (Short, hair-like, thin appendages) when present as
attachment or conjugation pili
• Cell division by binary fission (DNA molecule is replicated,
separated and attached to the cell membrane; then
the cell splits into two identical cells, each containing
an exact copy of the original cell's DNA)
•Bacteria can perform both anaerobic and aerobic
respiration
• Many aquatic bacteria have gas vacuole (filled with gas)
enable the bacteria to float

4. Biological Importance of Bacteria
1) Some make antibiotics (Streptomyacin)
2) Provide enzymes for biological washing powders
3) Used as microbial insecticides
4) Used to make biodegradable plastics & leach out metals
5) Decomposers – Analysis of dead bodies and substances
in soil, inside animals Enterobacteria – live inside
us, break down waste, make vitamins
6) Process foods – cheese, yogurt (convert lactose to lactic
acid), produce characteristic flavour

5. 7) Xanthan gum formed by certain bacteria is used as gelling
agent in many industries
8) Bacteria are used in molecular research, genetic
engineering, and medical research
9) Some bacteria ferment sugars & organic acids and produce
ethanol, methanol, acetone, lactic acid & acetic acid
10) Bacillus thuringiensis (BT) used as biological control of
pests. BT reproduce only in intestinal tract of caterpillars
which are killed by toxin from the bacterium

6. 11) Lactobacillus used in the dairy, beverage and baking
industries. Used in production of wine, beer and other
commercial products
12) Actinomycetes (nonphotosynthetic bacteria with
branched filaments) were original source of antibiotics
as tetracycline, neomycine, erthromycin & streptomycin
Streptomycin is produced by Streptomycetes
13) The cyanobacterium Spirulina has a dry weight
protein content of about 70 %.
So it is used as a nutritional food supplement