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Current Category » Introductory Plant Pathology

Classification of Bacteria or Prokaryotes – Volume II

The classification of bacteria or prokaryotes (of significance in agriculture and allied fields) given in “Bergey’s Manual of Systematic Bacteriology” is listed as follows.

Volume II:

Gram Positive Cocci:

In this section, 15 diverse genera of bacteria are placed together only because they are non-spore forming, chemo-organotrophic, Gram – positive cocci. The two important families are i) Deinoccaceae, ( Genus Deinococcus ) ii) Micrococcaceae , ( Genera: Micrococcus, Planococcus and Staphylococcus).  
Micrococci are non-motile, aerobic, oxidative harmless saprophytes occurring in soil and fresh water. Planococci are also harmless saprophytes that occur in marine environments. Staphylococci are non-motile facultatively anaerobic parasites. Major pathogenic species is S. aureus, causing wound infections, postoperative infections, food poisoning (Stapholococcai) in humans and mastitis in cattle.  
Other genera are Streptococcus, aerotolarant, homofermentative (end product of sugar fermentation is lactic acid only), most are pathogenic to humans and animals. E.g. S. pyogenes causes sore throat, scarlet fever and other human infections, S.mutans, inhabit in human oral cavity and cause dental caries, S. facalis, inhabit in the intestinal tracts humans and animals causing urinary tract infections, S.lactis and S. cremoris are harmless contaminants of milk and dairy products and therefore, widely used as “Starter cultures” in the manufacture of buttermilk and cheeses, S. Pnemoniae, also called Pneumoccus causing lobar pneumonia in humans.

Leuconostocs are harmless saprophytes occurring in grass, silage, grape leaves and spoiled food. They are hetero fermentative, producing CO2 and ethanol or acetic acid in addition to lactic acid and are often used as starter cultures for manufacture of butter, buttermilk, and cheese.

Section 13: Endospore Forming Gram: Positive Rods and Cocci

The important genera under this section are:

i) Bacillus:

Species such as, B. subtilis and B. cereus are mesophilic saprophytes producing exoenzymes that hydrolyze starch and casein, later species can cause a type of food poisoning. B. stenothermophilus, is thermophilic species associated with spoilage of canned foods, B.Polymyxa, has ability of N2 fixation under anaerobic conditions, B.turingiensis and B. popillae are pathogenic to insects, E.g. b.propillae, cause milky disease of Japanese better grub , B.anthracis is the only species of Bacillus that is highly pathogenic to humans and animals causing anthrax disease.

ii) Sporosarcina:

This genus contains cocci that are arranged in tetrads or cubical packets of eight cells. They are widely distributed in fertile soil where they decompose urea.

iii) Clostridium:

Members of the genus are fermentative and same species are important in agriculture. i.e. C. botulinum, causes food poisoning known as botulism, C.tetani, cause tetanus in humans, C.perfringes, cause wound infections (gas gangrene) and food poisoning; C. pasteurianum, mesophile inhabiting in soil and having ability to fix N2.

iv) Desulfatomaculum: Sulfate Reducing Bacteria:
Section 14: Non Spore forming Gram-Positive Irregular Shaped Rods:

This section includes heterogenous and variety of bacteria with aerobic or facultative anaerobic nature and, filamentous or non filamentous rods. Some of the important genera are:

a. Corynebacterium:

These are saprophytes occurring in soil and water, animal and human parasites and pathogens, e.g. C.diphtheriae cause diphtheria in humans, also causes diseases in plants.

b. Arthrobacter:

Soil saprophytes with characteristics rod-cocous cycle. i.e. cells in log phase are irregular rods and cell in stationary phase are coccoid.

c. Microbacterium:   
These are saprophytes occurring in milk, dairy products and diary equipments.

d. Cellulomonas:

The species are important cellulose decomposer or degrading bacteria.

Section 16: Mycobacteria:

Contain a single Genus Mycobacterium, these are aerobic, slightly curved or straight rods, cell wall contains 90% mycolic acid and are acid-fast in staining reaction. Many species are pathogenic to humans. E.g. M.tuberculosis cause tuberculosis and M.leprae, causes leprosy disease in human.


Current Category » Introductory Plant Pathology