Microbial hydrolysis products

RAPP c, LANTZSCH H J, DROCHNER w (2001) Hydrolysis of ph)dic acid hy intrinsic plant and supplemented microbial phytase Aspergillus niger) in the stomach and small intestine of minipigs fitted with re-entrant cannnlas. 3. Hydrolysis of ph)dic acid (1P6) and occurrence of hydrolysis products (1P5,1P4, 1P3 and 1P2). JAnim Physiol Anim Nutr (Berl). 85 420-30. 

These species are ubiquitous in soil (Kelly and Harrison 1989). In a recent laboratory investigation of the fate of ionic thiocyanate in six different soils, Brown and Morra (1993) concluded that microbial degradation is the primary mechanism for thiocyanate disappearance at or below 30 °C, with carbonyl sulfide proposed as a possible hydrolysis product. Loss of thiocyanate at higher temperatures (50-60 °C) did not appear to result from microbial degradation the observed decreases in thiocyanate concentrations of soil extracts with incubation time at elevated temperatures were postulated to result primarily from increased sorption or increased sorption kinetics, but abiotic catalysis of thiocyanate degradation was also noted as a possible cause. 

Matsumura and Bousch (1966) isolated carboxy lest erase (s) enzymes from the soil fungus Trichoderma viride und a bacterium Pseudomonas sp., obtained from Ohio soil samples, that were capable of degrading malathion. Compounds identified included diethyl maleate, desmethyl malathion, carboxylesterase products, other hydrolysis products, and unidentified metabolites. The authors found that these microbial populations did not have the capability to oxidize malathion due to the absence of malaoxon. However, the major degradative pathway appeared to be desmethylation and the formation of carboxylic acid derivatives. 

A Flavobacteriumsp. (ATCC 27551), isolated from rice paddy water, degraded parathion to 4-nitrophenol. The microbial hydrolysis half-life of this reaction was <1 h (Sethunathan and Yoshida, 1973 Forrest, 1981). When parathion (40 pg) was incubated in a mineral salts medium containing 5-day-old cultures of Flavobacterium sp. ATCC 27551, complete hydrolysis occurred in 72 h. The major degradation product was 4-nitrophenol (18.6 iig) (Sudhaker-Barik and Sethunathan, 1978a). 

Hydrolysis products that may form in soil and in microbial cultures include A-phenyl-3-chloro-carbamic acid, 3-chloroaniline, 2-amino-4-chlorophenol, monoisopropyl carbonate, 2-propanol, carbon dioxide, and condensation products (Rajagopal et al., 1984). The reported half-lives in soil at 15 and 29 °C were 65 and 30 d, respectively (Hartley and Kidd, 1987). 

With respect to the hydrolysis step, it can be accomplished by acid, by enzymatic, or by direct microbial attack. Microbial hydrolysis results primarily in the production of cellular biomass or single-cell protein. Acid hydrolysis, while simple and direct, results in a sugar syrup with considerable contamination from the side reaction products. Enzymatic hydrolysis is usually the cleanest hydrolysis process. Unfortunately, it is the most costly of the three to operate. 

Several alternatives are used to reduce ammonia elimination. Applied in relatively small quantities, urease inhibitors such as A-(n-butyl) thiophosphoric acid triamide reduce the rate of microbial hydrolysis of urea and increase its efficiency as a fertilizer (Manahan, 2005). Ammonia volatilization could also be reduced using a mixture of urea with tropical peat soil or free humic substances, such as humic and fulvic acids, isolated from peat soils (Bernard et al., 2009). Another application of green technologies is the use of thermal polyaspartate, a product formed by the condensation and base treatment of a natural compound, aspartic acid. This has been found to be effective in stimulating plant uptake of fertilizer thus reducing the amount of fertilizer required (Manahan, 2005). 

Trichlorophenoxvacetic Acid. 2,4,5-Trichlorophenol, the hydrolysis product of 2,4,5-T, did not condition the soil for enhanced biodegradation of 14C-2,4,5-T (Table I). The 2,4,5-trichlorophenol, unlike 2,4-dichlorophenol, did not serve as a suitable microbial substrate. 

Diazinon. 2-Isopropyl-6-methyl-4-hydroxypyrimidine, the hydrolysis product of diazinon, did not condition the soils for enhanced degradation of diazinon (Table II). Despite the low microbial toxicity and high availability (discussed elsewhere in this chapter), the hydroxypyrimidine metabolite did not predispose soils for rapid degradation of diazinon. Enhanced biodegradation of diazinon in rice soils has been previously reported (1). Evidently, the soil we studied did not contain microbes capable of adapting for diazinon enhanced degradation. 

Isofennhos. Exposure of soils to salicylic acid, the secondary hydrolysis product of isofenphos, resulted in enhanced degradation of isofenphos (Table IV). Nearly two-thirds of the applied isofenphos was converted to soil-bound residues in soil pretreated 3 and 4 times with salicylic acid. Seventy-eight percent of the applied isofenphos was recovered at the end of the 3-week incubation in the control treatment as compared with 34 to 65% in soils pretreated with salicylic acid. The ability of microbes to metabolize structurally similar compounds such as 3,5-dichlorosalicylate, 3,6-dichlorosalicylic acid (24), and 5-chlorosalicylate (25) to their benefit has been reported. The low microbial toxicity, relative availability (as discussed later in this chapter), and nutritive value of salicylic acid may contribute to its potential to condition soils for enhanced degradation of isofenphos. 

Another important variable that determines the microbial metabolism of soil-applied pesticides is the availability of the chemical to the microbial systems degrading it. The hydrolysis product and parent pesticide should be available to microbes so as to exert their toxicity or provide nutrient value. The lack of availability of some chemicals may result in resistance to microbial adaptation. 

Implications of Mobility on the Availability and Degradation of Pesticides in Soil. Repeated application of 2,4-dichlorophenol, p-nitrophenol, and salicylic acid (as observed in current studies) and carbofuran phenol (20) has induced enhanced microbial degradation of their parent compounds. Rf values of these hydrolysis products indicate intermediate to high mobility in soils. The p-nitrophenol, 2,4-dichlorophenol, and salicylic acid were utilized as energy sources by microbes, and their availability in soil may contribute to the induction of rapid microbial metabolism. Carbofuran phenol did not serve as a microbial substrate but also enhanced the degradation of its parent compound, carbofuran (20). Carbofuran phenol is freely available in anaerobic soils, but the significance of its availability is yet to be understood. 

The hydroxypyrimidine hydrolysis product of diazinon is more readily available in all soils tested and is mineralized by microbes (33). Our Microtox studies have demonstrated its low toxicity to bacteria. Availability, low microbial toxicity, and susceptibility to microbial metabolism of this hydrolysis product may favor enhanced degradation of its parent compound in soils with populations of degrading microorganisms, but no adaptation was noted in our laboratory studies. 

Chlorpyrifos is immobile in soil and is not available to microbes. However, its pyridinol hydrolysis product is relatively mobile its microbial toxicity and availability in soil may contribute to the increased persistence of chlorpyrifos observed in pyridinol-treated soils. 

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