4.5 AZOBACTER AND RHIZOBIUM

1. 4.5 AZOBACTER AND RHIZOBIUM

2. Introduction • Both are soil bacteria • Azobacter and Rhizobiaceae bacterial species are nitrogen fixers • Azobacter is a free-living bacteria • Rhizobium basically in soil • Most bacteria in soil are about one micron in length or diameter. • Their size varies with their environment. • Bacteria in -high levels of nutrients ,larger than those in nutrient- poor .

3. Azobacter

4. Azobacter - Soil bacteria • The majority of bacteria in soil usually occur as single cells. • Bacteria sometimes join together in chains or clusters. They mainly have one of two shapes - spheres (called cocci) and rods (called bacilli). • Other bacteria have more varied shapes including spirals and long thin hyphae(although these are less common).

6. Forms of Nitrogen • Urea  CO(NH2)2 • Ammonia  NH3 (gaseous) • Ammonium  NH4 • Nitrate  NO3 • Nitrite  NO2 • Atmospheric Dinitrogen N2 • Organic N

7. Roles of Nitrogen • Plants and bacteria use nitrogen in the form of NH4+ or NO3- • It serves as an electron acceptor in anaerobic environment • Nitrogen is often the most limiting nutrient in soil and water.

8. Nitrogen is a key element for • amino acids • nucleic acids (purine, pyrimidine) • cell wall components of bacteria (NAM).

9. As nitrogen fixer • These bacteria take nitrogen from the air (which plants cannot use) and convert it into a form of nitrogen called ammonium (NH4+), which plants can use. • The nitrogenaseenzyme controls the process, called nitrogen fixation, and these bacteria are often called "nitrogen fixers".

10. It converts atmospheric nitrogen into ammonium, but in the condition of : • An easily degradable carbon source is available • Any nitrogen compounds such as ammonium or nitrate, are not already present in substantial concentrations • Soil pH levels are between 6 and 9 • High levels of phosphorus are present • Very low levels of oxygen are present

11. Benefits as biofertilizer • These are primarily used to enhance the growth of several species of plants and crops. • A correct proportion of bacterial growth could ensure a high quality of biofertilizer • Its capability in maintaining the pH, safe to use and compatible as chemical fertilizer

12. Rhizobium • Rhizobium is primarily a gram negative, motile, non-sporulatingrod that requires a plant host. • Species under this genus: • R. phaseoli • R. leguminosarum • R. trifolii • Other genus are cowpeas Rhizobium and Bradyrhizobium

13. In agricultural • Rhizobia belong to a specific group of bacteria that form a mutually beneficial association, or symbiosis, with legume plants. • Rhizobia are found in soils of many natural ecosystems. They may also be present in agricultural areas where they are associated with both crop legumes (like soybean) and pasture legumes (like clover). • Usually, the rhizobia in agricultural areas have been introduced at sowing by applying an inoculumto the exterior of the seeds as liquid formations or pellets.

14. Rhizobium

15. 4.6 enterobacteriaceae Enteric Gram negative aerobes rods

16. Sub-grouping

17. Morphology • Gram negative • Non-sporing • Rods • 1-4 X 0.6µm

18. Motility • Mostly surrounded by flagella (peritrichous) and are motile • Non-motile enterobacteriaceae are Shigella and Klebsiella • In Escherichia and Morganella, most of the strain are motile, but some are non-motile • Special case like Yersinia, contain species that are motile at 25oC but non-motile at 35 – 37oC

19. klebsiella E.coli

20. Culture • Most will grow in wide temperature range in ordinary culture media including NA and BA • Selective media is required to recover Salmonella and Shigella • On BA, enterobacteria produce large, shiny, grey colonies that may be hemolytic • Species that produce hydrogen sulphideoften show a green colour around the subsurface colonies(Klebsiella) and capsulated strains (Escherichia) produce large mucoid colonies.

21. E.coli In nutrient agar In MacConkey agar

22. Klebsiella sp In macconkey agar In blood agar

23. Salmonella sp In ss agar In xld agar

24. Toxin production • Exotoxin (enterotoxin) is produced by Shigelladysenteriae and toxigenic strain of Escherichia coli (ETEC) • When lysed, enterobacteria will releaseendotoxin from their cell wall *The feature above is applied to all Gram negative rods

25. Serology • There are three antigens possesed by some or all enterobacteria • O, or somatic antigens, found in the wall of bacterial cell. These antigen are used to subgroup enterobacteria such as Salmonella and Escherichia sp. O antigen is heat-stable. • K, or surface antigen, found surround the cell wall and can therefore interfere with O antigen grouping. They can be inactivated, however, by heat. Eg. Vi antigen for Klebsiella and B antigen for strain of E.coli • H, or flagella antigen, posesses by motile enterobacteria, they are found in the flagella and are heat-labile. H antigens are used to identify Salmonella serovars within their somatic groups

26. Antigenic structure of Enterobacteriacea

27. TASKS • DISCUSS 5 GENUS OF ENTEROBACTERIACEAE • INCLUDE –MORPHOLOGY, BIOCHEMICAL CHARACTERISTIC, IMPORTANCE OF THE CULTURE.

28. The end