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.

Bacteria: Disadvantages

• Bacteria are our 'foes' as they are associated with several diseases of plants and animals including man due to parasitic mode of nutrition of some bacteria. Bacterial attack is less severe on plants than it is on animals.
• Important bacterial diseases on plants are:
  1. Canker of Citrus (citrus canker) Xanthomonas citri
  2. Angular leaf spot of cotton X. malvacearum
  3. Fire blight of apples Erwinnia amylovora
  4. Crown gall of crops Agrobacterium tumefaciens
  5. Tondu of wheat Corynebacterium tritici
     • Important bacterial diseases on man are:
  6. Cyphillis Tryponema pallidum
  7. Plague (Black Death) Pasteurella pestis (Y. pestis)
  8. Chlorea Vibrio cholerae
  9. Anthrax Bacillus anthracis
  10. Pneumonia Diplococcus pneumonae
  11. Tuberculosis (TB) Mycobacterium tuberculoses
  12. Typhoid (Enteric fever) Salmonella typhi
  13. Bacterial dysentery Bacillus dysentrae (Shigella)
  14. Amoeboid dysentery Entamoeba histolytica (Protozoa)
  15. Tetanus (Lock jaw) Closteridium tetani
  16. Ptomaine (deadly food poisoning) Closteridium botulinum
  17. Leprosy Bacillus lepri (Mycobacterium lepri)
  18. Diptheria Corynebacterium diptherae
  19. Erysepalas (deadly blood Streptococcus

Poisoning; Death of RBC's)

20. Whooping cough Bordetella partusis
21. Gonorrhoea Neisseria gonorrhoae

Bacterial diseases like cholera, typhoid, dysentery etc are water borne diseases: tuberculosis, plague etc are air-borne diseases whereas disease like tetanus spreads through wounds. Syphilis is transmitted through sexual contact. Transmission of leprosy through contact is a matter of dispute. India based Mother Teresa was awarded Nobel Prize for her service to leprosy patients in West Bengal and other parts of India

Bacteria : Forms

1. On the basis of shape, bacteria may be cocci (Singular coccus), Bacilli (Bacillus), Vibrio, Spirillum etc. Cocci are spherical bacteria, smallest in size. They may be single (monoococucus), in pairs (Diplococcus), in chains (streptococcus), in bunches (staphylococcus) or cuboid (sar cinnae). Bacteria causing pneumonia are Diplococcus Bacilli are rod shaped bacteria they may be single or in chains (Streptobacilli). Majority of parasitic bacteria are rod shaped bacteria. Streptobacilli surrounded by mucilaginous sheath form Zoogloea. Vibro are comma shaped bacteria. Bacteria causing cholera are vibrio bacteria. Spirillum and spirochaete are zigzag spring like bacteria, Spirillum volutans is recognized as largest bacteria. The terms like coccus, bacillus, vibrio etc were coined by Mueller.
2. On the basis of cilia, a bacterial cell may be:

Atrichous : Bacterial cell without cilia.

Monotrichour : Bacteria cell with single cilia.

Lopotrichous : Bacteria cell with tuft of cilia at one end.

Cephalotrichous : Bacterial cell with tuft of cilia at both the ends.

Amphitrichous : Bacterial cell with one cilia at both the ends.

Peritrichous : Bacterial cell with cilia throughout the body.

Bacteria causing cholera disease is comma shaped & Lophotrichous.

3. On the basis of nutrition, bacteria may heterotrophy or autotroph. Heterotroph bacteria are further divided as saprophytic bacteria & parasitic bacteria. Similarly, autotroph bacteria are further divided as chemosynthetic and photosynthetic bacteria.
   • Bacteria, which obtain their food from dead organic matter, are saprophytic bacteria. They perform significant role of decomposers in ecosystem. Bacteria, which obtain their food from other living entity, are called parasitic bacteria. The living entity, which provides food to parasite, is termed as host. Host-parasite relation is specific. Parasite is called pathogen when it spreads in host.
   • Bacteria, which obtain their food through the inorganic reactions in which they participate, are called chemosynthetic bacteria. They are named after the inorganic reactions, us that they are involved. Thus, N-Bacteria S-Bacteria & Fe-Bacteria etc are examples of chemosynthetic bacteria. Chemosynthetic bacteria are basically autotroph but do not require pigment chlorophyll for energy requirement. Chemosynthetic bacteria will survive alone if chlorophyll pigment disappears from the world; rest will perish.
   • Bacteria, which obtain chemical energy through glucose formation, are called photosynthetic bacteria. They are autotrophs and depend on chlorophyll like pigments i.e., Bacteriochlorophyll & chlorobium chlorophyll (Bacterio viridies) for glucose formation. Green-S-Bacteria, Purple-S-Bacteria & Rhodospirillium etc. are examples of photosynthetic bacteria.

Comparison between normal and bacterial photosynthesis
Normal Photosynthesis	Bacterial Photosynthesis
1. Raw materials are CO2 & H2O	1. Raw materials are CO2 & H2S
2. H for reduction of CO2 into glucose comes from H2O	2. H- for reduction of CO2 into glucose comes from H2S.
3. Principal pigment is chlorophyll a	3. Principal pigment Bacteriochlorophyll a.
4. Intermediate H-acceptor is NADP	4. Intermediate H-acceptor is NAD.
5. PS I & PS II both are present in light phase.	5. PS I only is present in light phase; PS II is absent.
6. O2 is released as by product	6. S is released as by product
7. Biochemical reaction 6CO2 + 12H2O = C6H12O6+6H2O+6O2	7. Biochemical reaction. 6CO2 + 12H2O = C6H12O6+6H2O+12S
Generalised equation for both of the above 6CO2 + 12H2A = C6H12O6 + 6H2O + 12A A may be oxygen or sulfur.

Photosynthesis in bacteria was first studied by Van Neil of Germany who was first to support the idea of Robino Hill that O₂ released in normal photosynthesis comes from H₂O and not from CO₂.

Bacteria: Introduction

1. Study of Bacteria is called 'Bacteriology'. Leeuwenhoek is recognized as pioneer worker in Bacteriology. Pasteur, Koch & Lister are other earlier workers in Bacteriology.
2. The term bacteria were coined by Ehrenberg for the smaller 'animalcules' or the 'wretched beasts' of Leeuwenhoek. Bacteria are found everywhere and in all sorts of climates however they do not survive in acidic medium of Pickle solution or highly concentrated sucrose solution due to plasmolysis.
3. Bacteria activity is reduced greatly at low temperature; this explains why foodstuff remains safe for longer period in cold devices like fridge and refrigerators etc. Bacteria behave in different manner in different range of temperature.