Bacteria: Advantages:

Bacteria are our friends as they are associated with several advantages in various forms. Some of them are:

1. Bacteria & Ecosystem: Saprophytic bacteria along with saprophytic fungi perform useful role of decomposers in ecosystem. Decomposition of organic matter in absence of O₂ is called putrefaction and breakdown of organic matter in presence of O₂ is called decay. Highly un-decomposed organic matter is litter; partly decomposed organic matter is humus and highly decomposed organic matter is called humus.
2. Bacteria & Industry: Lactobacillus laciti and Streptococcus lacti convert milk into curd. Acetobacillus aciti changes sugar solution into vinegar. Flavour in tea leaves by Micococcus condensa and in tobacco leaves by Micococus megatherium develops due to fermentation activity of bacteria. Retting involves separation of plant fibers after decomposition of non-cellulosic materials by various species of Closteridium like C.butyricum and C.felsineum.
3. Bacteria and N-cycle system: Nitrogen is first essential element in terms of requirement for proper growth of plants. It is required in protein synthesis, chlorophyll synthesis and also in synthesis of nucleic acids. Plants cannot utilize molecular nitrogen directly. The plants mainly in the form of nitrates absorb it. Nitrogen changes into nitrate via ammonia formation. Some bacteria control N-cycle, which comprises Nitrogen fixation, Nitrification and Denitrification. Nitrogen fixation involves conversion of N₂ into ammonia. Bacteria which participate in N-fixation are Closteridium, Azotobacter and Rhizobium etc. Closteridium and Azotobacter and asymbiotic biological N fixing bacteria whereas Rhizobium is symbiotic biological N-fixing bacteria are present in root nodules of Leguminous or papilionaceous plants. Klebsiella is leaf nodule N-fixing bacteria. Frankia is non-leguminous N-fixing bacteria 'nif' genes control biological N-fixation. Mechanism of biological N-fixation by bacteria was first studied by Heijerinck whereas Winogradasky studied biological N₂ fixation by some blue green algae.
   • Conversion of NH₃ into nitrite is termed as initial stage of Nitrification. A bacterium which participates in initial stage of nitrification is nitrosomonas Conversions of nitrite into nitrate is called final stage of nitrification. Nitrobacter is the bacteria which participates in final stage of nitrification.
   • Release of Nitrogen from Macromolecules of Nitrogen is called denitrification. Bacillus denitrificans is the bacteria involved in denitrification. The summary of Nitrogen cycle is given in the following figure:

Summary of various N-fixing bacteria:

• Azotobacter, Thiobacillus, Mycobacterium etc. : Free living & aerobic.
• Closteridium Klebsiella : Free living & anaerobic.
• Rhizobium, Aopzprirllium Frankia : Symbiotic & anaerobic
• Citrobacter : Symbiotic and anaerobic
  • Bacteria & Antibiotics: Though first antibiotic penicillin was obtained from ascomycetes fungus Penicillium notatum by Alexander Flemming in 1929, yet soil-borne bacteria Streptomyces of actinomycetes (ray fungi) are rich source of various types of antibioitics. Antibiotics are chemical inhibition. The term 'antibiotic' was coined by Salman Waksman. Antibiotics are known as chemotherapeutic agents. Some of the antibiotics extracted from bacteria are bacitracin, subtilin, polymyxin, gramicidin etc.

Salient features of some antibiotics chemotherapeutic agents

Name of the antibiotics	Name of the discover	Source of antibiotics	Action of antibiotics
Penicillin	Alexander Flemming	P. notatum P. chrysogenum	Breaks muco complex cell wall of bacteria.
Streptomycin	Waksman	Streptomyces griesus	Inhibits synthesis of 30S fragment of ribosome in bacteria.
Erythromycin	Mc Guire	S. erythreus	Inhibits synthesis of 50S fragment of ribosome in bacteria
Chloromycin	Burkholder	S. venezualae	Inhibits initiation of protein synthesis in bacteria.
Aureomycin	Duggar	S. auerofaciens	Inhibits formation of tRNA amino acid complex.
Terramycin	Pfizer Ltd.	S. rimosus	Inhibits formation of tRNA amino acid complex.

Penicillin is not broad spectrum antibiotic because it is more active on gram positive bacteria, less effective on gram negative bacteria. Streptomycin is first brad spectrum antibiotic which is equally active on gram positive and gram negative bacteria both.

• Bacteria & Miscellaneous uses

1. Aerobacter aerogenes decomposes DDT whereas Flavobacterium and Corynebacterium decompose 2, 4-D etc. DDT and 2, 4-D are non-biodegradable chemicals, which may be lethal even.

2. Bacillus pudita, pseudomonas and some other oil-eating bacteria help in cleaning up oil spills. They thus help in preventing water pollution of seas/oceans caused due to oil refineries.
3. Anand Mohan Chakroborty has developed genetically engineered bacteria named Superbug that feeds on oil spills.
4. Bacterium Methylophylus methylotropous is source of single cell protein (SCP) the product was called 'Pruteen'. Fungus Fusarium is also used for the purpose i.e. preparation of mycoprotein on larger scale.
5. Batch culture & continuous culture are two main methods of fermentation on larger scale. The former is closed system whereas latter is open system.