Soil microbes

A recent suggestion has been to use plants to stimulate the microbial degradation of the hydrocarbon (hydrocarbon phytoremediation). This has yet to receive clear experimental verification, but the plants are proposed to help deUver air to the soil microbes, and to stimulate microbial growth in the rhizosphere by the release of nutrients from the roots. The esthetic appeal of an active phytoremediation project can be very great. 

Bacillus sp. These bacteria are gram-positive soil microbes. Members of the Bacillus species supply 58% of iadustrial enzymes sold (19). Eor example, proteases from B. amjloliquefaciens and amylases from B. licheniformis glucose isomerase from B. coagulans are used ia a variety of iadustrial processes (see Enzyme applications-industrial). The proteiaaceous iaclusioas produced by B. thuringiensis are useful as iasect toxias. Thus exteasive fermentation technology has been developed for Bacillus species and low cost media are available (19). 

Degradation or Transformation. Degradation or transformation of a herbicide by soil microbes or by abiotic means has a significant influence not only on the herbicide s fate in the environment but also on the compound s efficacy. Herbicides that are readily degraded by soil microbes or other means may have a reduced environmental impact but may not be efficacious. Consider the phenomenon of herbicide-resistant soils. In these cases, repeated application of a given herbicide has led to a microbial population with an enhanced ability to degrade that herbicide (252,253). This results in a decrease or total loss of the ability of the herbicide to control the weed species in question in a cost-effective manner. 

Soil type and structure also influence the dynamics of rhizosphere microbial populations. Whether nutrients are available for bacteria in the rhizosphere often depends on the sites in the soil where nutrients are present. Organic compounds tightly bound to the soil matrix are often less available for bacteria (226), and those present in smaller pore spaces can be physically protected against mineralization. However, disturbance of the soil often cau.ses these nutrients to become more available to soil microbes (227). 

D, A. Phillips, Flavonoids Plant signals to soil microbes. Phenolic MeUihoUsm in Plants (H. A. Stafford and R. K. Ibrahim, eds.), Plenum Press, New York, 1992,... 

The classic seed burial studies of W. J. Beal and his successors have shown seeds of at least one weed species, Moth Mullein (Verbascum blattaria L.) can remain viable in soil for a peiod of 100 years, whereas three species continued to germinate after 80 years of burial (30). Weed seeds not only resist decay by soil microbes, but they vary in dormancy characteristics. There is considerable evidence that chemical inhibitors are responsible for both phenomena. Unsaturated lactones and phenolic compounds in particular, are potent antimicrobial compounds present in many seeds (4J. Fruits and seeds are also known to contain diverse germination inhibitors including phenolic compounds, flavonoids and/or their glycosides and tannins. Unique methods to destroy inhibitors could provide an excellent weed management strategy. 

Rhizodegradation is a symbiotic relationship that has evolved between plants and soil microbes. The plants provide the nutrients necessary for the microbes to thrive, and the microbes provide a healthier soil environment in which the plant roots can proliferate. 

Patel BK, Patel HR (1997) Effect of soil solarization, tabbing, nematocides and green manuring on soil microbes in bidi tobacco nursery. Indian J Environ Toxic 7 42-46 Patel HR, Makwana MG, Patel BN (1995) The control of nematode and weeds by soil solarization in tobacco nursery effects of the film thickness and of the covering duration. Plasticulture 107 21-27... 

Hurt RA, Qiu X, Wu L, Roh Y, Palumbo AV, Tiedje JM, Zhou J (2001) Simultaneous recovery of RNA and DNA from soils and sediments. Appl Environ Microbiol 67 4495 1503 Ingham ER, Troymow JA, Ames RN, Hunt HW, Morley CR, Moore JC, Coleman DC (1986) Trophic interactions and nitrogen cycling in a semi-arid grassland soil. Part 2. System responses to removal of different groups of soil microbes or fauna. J Appl Ecol 23 615-630... 

Soil microbes. Effects include reduced microbial biomass and/or species diversity, thus affecting microbial processes such as enzyme synthesis and activity, litter decomposition, associated with carbon and nitrogen mineralization, and soil respiration ... 

Possible effects on soil hfe, plants (phytotoxicity) and on ground water are of concern in all types of ecosystems. Food quality criteria are, however, of relevance for arable land only, whereas possible secondary poisoning effects on domestic animals or terrestrial fauna are relevant in grassland and non-agricultural land. A final critical limit can be based on the most sensitive receptor. Even though effects vary for each metal, soil microbes and soil fauna are generally most sensitive. 

According to the heavy metals effects, the soil microbes, crops and ground waters as a source of drinking water, are the most important receptors. During migration in the food web, the heavy metals, especially Cd and Hg, can affect also higher organisms,... 

Verona and Picci (U9) have shown that the phosphorus contained in Hanane was used by the soil microbes for their nutrition in relation with studies conducted on the breakdown of systemic insecticides. Pianka, as cited by Nicol (32), has reported that it is possible to enhance the activity of systemic insecticides by the addition of certain chemicals not necessarily systemic. Samples of dimefox activated by... 

Microorganisms. Diflubenzuron was stable to degradation by uncharacterized microorganisms from a sewage lagoon (12). Pseudomonas putida (soil microbe) also was unable to metabolize ... 

Reports are published on the metabolism of methoprene by plants (25), aquatic microorganisms (26), soil microbes (27), house flies and mosquitoes in vivo (28), resistant house flies in vivo and in vitro (29), a steer (30), a lactating cow (31), chickens (32), and bluegill fish (33). In addition, radioactive material balance studies have been published for a guinea pig, steer, and cow (34), chickens (35), and rats (36, 37), including whole-body autoradiography in rats (37). 

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