Bacteria nutrient cycling

Enhanced nutrient cycling in both the rhizosphere and bulk soil may depend on the bacterial grazing by protozoa or nematodes with release of inorganic N. Nematodes appear to be the primary consumers of bacteria in the rhizosphere, whereas protozoa are equally prevalent in rhizosphere and bulk soil (41,97). Estimated C-to-N ratios of bacterial-feeding nematodes range from 5 1 to 10 1 (98,99) and are generally higher than those of their bacterial food source thus the excess N is excreted as ammonia (100,101) by nematodes. The estimated... 

Microbial communities play an essential role in nutrient cycling and in the fate of trace metals in aquatic environments and in engineered systems (e.g., wastewater treatment plants). However, some of the microorganisms (e.g., nitrifying bacteria) are quite sensitive to metals in aquatic environments (Twiss et al., 1996). The HMBC... 

Ingham R. E., Trofymow J. A., Ingham E. R., and Coleman D. C. (1985) Interactions of bacteria, fungi, and their nematode grazers effects on nutrient cycling and plant growth. Ecol. Monogr. 55, 119—140. 

As said above, plant root chemistry may also influence deeply alpine soil microorganism s biomass. It turns out that the particular chemical composition of exudates is a strong selective force in favour of bacteria that can catabolize particular compounds. Plants support heterotrophic microorganisms by way of rhizodeposition of root exudates and litter from dead tissue that include phenolic acids, flavonoids, terpenoids, carbohydrates, hydroxamic acids, aminoacids, denatured protein from dying root cells, CO2, and ethylene (Wardle, 1992). In certain plants, as much as 20-30% of fixed carbon may be lost as rhizodeposition (Lynch and Whipps, 1990). Most of these compounds enter the soil nutrient cycle by way of the soil microbiota, giving rise to competition between the myriad species living there, from microarthropods and nematodes to mycorrhiza and bacteria, for these resources (e.g. Hoover and Crossley, 1995). There is evidence that root phenolic exudates are metabolized preferentially by some soil microbes, while the same compounds are toxic to others. Phenolic acids usually occur in small concentration in soil chiefly because of soil metabolism while adsorption in clay and other soil particles plays a minor role (Bliun et al., 1999). However, their phytotoxicity is compounded by synergism between particular mixtures (Blum, 1996). 

Estuarine circulation also plays an important role in nutrients cycles in stratified bays. The organic matters deposit on the seabed after phytoplankton blooms or the river runs off. It is decomposed by bacteria in the seabed. These nutrients are supplied from the seabed under anoxic condition in summer. Seasonal variations in nutrient concentrations in bottom water are consistent with these phenomena, indicating that high concentrations of phosphate and ammonimn in bottom water (Fig. 32.3). 

Microbial insecticides are very complex materials in their final formulation, because they are produced by fermentation of a variety of natural products. For growth, the bacteria must be provided with a source of carbon, nitrogen, and mineral salts. Sufficient nutrient is provided to take the strain of choice through its life cycle to complete sporulation with concomitant parasporal body formation. Certain crystalliferous bacilli require sources of preformed vitamins and/or amino acids for growth. Media for growing these bacilli may vary from completely soluble, defined formulations, usable for bench scale work, to rich media containing insoluble constituents for production situations (10,27). Complex natural materials such as cottonseed, soybean, and fish meal are commonly used. In fact, one such commercial production method (25) is based on use of a semisolid medium, a bran, which becomes part of the final product. 

In each cycle, the library of mutated genes is first inserted in a standard bacterial host such as Escherichia coli or Bacillus subtilis. Subsequently, bacterial colonies are plated out on agar plates and harvested individually by a colony picker. Each colony is placed in a separate well of a microtiter plate containing nutrient broth, so that the bacteria grow and produce the protein of interest. Because each colony originates... 

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