Dan Levanon

Roles of fungi and bacteria in the mineralization of the pesticides atrazine, alachlor, malathion and carbofuran in soil

Abstract Different roles for fungi and bacteria in the biotransfonnation pathways of pesticides in the soil were demonstrated. The pesticides studied were malathion (diethyl mercaptosuccinate S-ester 0,0 dimethyl phosphorodithioate), alachlor (2-chloro-N-[2-6-diethylphenyl]-N-[methoxy methyl] acetamide), atrazine (2-chloro-4-ethylainino-6-isopropylamino-l,3,5-triazine-2,4 diamine) and carbofuran (2,3-dihy-dro-2,2-dimethyl-7-benzofuranyl methylcarbamate). The mineralization of alkyl-side chains of alachlor and alkyl-amino-side chains of atrazine was found to be mainly due to fungal activity. Neither heterocyclic ring-labelled atrazine nor aromatic ring-labelled alachlor were degraded when fungi or bacteria were separately inhibited. The mineralization of carbofuran and malathion was mainly due to bacterial activity. These results indicate that the biodegradation of pesticides in the soil is performed by both fungi and bacteria. The mechanism of this phenomenon and the mode of action of the two microbial groups are discussed.

Protection against tabun toxicity in mice by prophylaxis with an enzyme hydrolyzing organophosphate esters

We demonstrate here the correlation between protection afforded by pretreatment alone with parathion hydrolase purified from Pseudomonas sp. against tabun toxicity in mice and the kinetic parameters which are assumed to determine the in vivo detoxification of tabun by the same enzyme. Results show that 15 and 22 micrograms of parathion hydrolase per animal conferred a protective ratio of 3.94 and 5.65 respectively, against tabun toxicity, without post-exposure treatment.

Degradation of atrazine by the lignocellulolytic fungus Pleurotus pulmonarius during solid-state fermentation

The biotransformation of atrazine added to a mixture of cotton and wheat straw (CWS) and inoculated with the white-rot fungus, Pleurotus pulmonarius, was studied, as a proposed system for bioremediation. The concentration of methanol-extractable atrazine was reduced, due to both biological transformation and physical-chemical adsorption to the straw. Only 32% of the total radioactivity added as 14C-ring-labeled atrazine to pasteurized CWS inoculated with Pleurotus was extracted two weeks after fungal colonization, and less than 70% from non-inoculated CWS. The reduction in extractable radioactivity increased with time of incubation. No mineralization of the triazine ring was found during six weeks of incubation, but transformation to two groups of atrazine metabolites, chlorinated and dechlorinated, occurred, as a result of the activity of the fungus inoculated and natural bacterial population. Unextractable radioactivity was recovered after digesting the colonized substrate with H2SO4, indicating adsorption of the herbicide and its metabolites to the straw. The results suggest that this process can be used to detoxify atrazine by both adsorption and biodegradation.

Chemical, physical and biological criteria for maturity in composts for organic farming

Properties of organic farming composts were examined during the composting process: pH, electrical conductivity, C/N ratio, total N content, NH4+ content, NO3−content, ash content, and organic matter content. In addition to these properties the respiration rate, microbial population counts, hydrolysis of Fluorescein Diacetate (FDA) and the activity of the enzyme amidase were studied. Composts at several stages of maturity were incubated in soil, and their N mineralization rates were measured. The end of the thermophilic stage was characterized by irreversible decrease in pile temperature to under 55°C, followed by stabilization of the chemical properties. This stage in the composting process is also characterized by decrease in CO2 evolution rate, changes in microbial populations and specific patterns in FDA hydrolysis and amidase activity. Based on this evidence, we suggest that biological parameters can be considered as indicators for compost maturity.

The effect of lignocellulose on lignocellulolytic activity of Pleurotus pulmonarius in submerged culture

SummaryThe possible effects of lignocellulose substrate on lignocellulolytic activity of the fungus Pleurotus pulmonarius was studied in submerged culture. This study included fungal growth rates, nitrogen and carbon consumption, and enzymatic activity rates, with and without added cotton-wheat straw (CWS) mixtures. Addition of CWS to the media caused increased consumption of glucose and NHinf4sup+by the fungal mycelium, induced carboxymethylcellulase (CMC-ase), increased poly-B decolourization, and enhanced the activity of laccase tenfold, while β-glucosidase activity was also enhanced: its first peak was higher and second peak earlier. Lignin peroxidase, however, was not detected. These results give some indication that the lignocellulolytic activity of P. pulmonarius in liquid culture is enhanced by the presence of lignocellulosic substrates such as CWS.

Chemical, Physical and Microbiological Considerations in Recycling Spent Mushroom Substrate

Spent mushroom substrates (SMS) have traditionally been discarded as wastes, creating an environmental nuisance. In recent years, mushroom growers all over the world are facing increasing pressure of environmental legislation, giving rise to the need for a more suitable solution for the disposal of SMS. At the same time, there is an increasing demand for organic residues and composts, which could provide several potential outlets for SMS. Agriculture, horticulture, soil reclamation projects and projects for the purification of contaminated soil, water and air are examples of such outlets. Each demands its own specific properties for the organic product. These properties are defined by chemical, physical and biological parameters. SMS should be treated to suit the specific demand of each outlet. The manipulation of SMS, mainly by recomposting, could produce products with several advantages over other recycled wastes. Such products could be used successfully to solve agronomic or environmental problems, whi...

Parathion degradation by a Pseudomonas sp. and a Xanthomonas sp. and by their crude enzyme extracts as affected by some cations

Abstract A Pseudomonas sp. and a Xanthomonas sp. were isolated from a pesticide disposal site in northern Israel. Both degraded parathion in two stages. In the first stage, p -nitrophenol (PNP) was released by a parathion hydrolase, while in the second stage PNP was degraded. The effect of Cu 2+ , Fe 2+ , Ca 2+ , Mn 2+ , Al 3+ , Zn 2+ and NaEDTA on parathion hydrolysis to PNP by growing cultures and by crude enzyme extracts of the isolates was studied. Parathion hydrolysis by both either living cells or crude enzyme extracts of the Pseudomonas sp. was inhibited by Cu 2+ even at a concentration of 20 μmoll −1 , as opposed to this cations stimulatory effect on the degradation of parathion by the Xanthomonas sp. Other cations investigated had a smaller effect on the rate of degradation by either bacterium. NaEDTA strongly inhibited parathion hydrolysis in the living cells, but not in the crude enzyme extracts of the Pseudomonas sp. In contrast, NaEDTA inhibited parathion hydrolysis in either living cells or crude enzyme extracts of the Xanthomonas sp.

Bulk treatment of substrate for the cultivation of Shiitake mushrooms (Lentinus edodes) on straw

A bulk treatment of substrate was developed for the cultivation of Shiitake mushrooms (Lentinus edodes) on a 1:1 mixture of cotton and wheat straws (CWS). The treatment is based on bulk pasteurization of CWS and the cultivation of mushrooms on 20-kg units of it. The advantages of this treatment lie in the reduction of energy and labor costs and the utilization of abundantly available wastes for mushroom cultivation.

Strain selection for cultivation of Shiitake mushrooms (Lentinus edodes) on straw

Abstract A two-stage method of strain selection was developed for optimal adaptation of the production of Shiitake mushrooms ( Lentinus edodes ) on straw substrate. The use of esterase isoenzymes, to indicate genetic variations, and mycelium growth rates, as a criterion for strain/substrate compatibility, were combined as tools for selection. The strains that were selected (four out of 22) developed fruit bodies on cotton and wheat straws mixtures (CWS), but only two of them gave yields on cotton straw (CS) alone. Biological efficiency reached 82% for CWS and 46% for CS in commercial-scale production trials.

Alfalfa saponins and microbial transformations of nitrogen in peat

Abstract Alfalfa saponins, their sugar fraction or glucose, but not their sapogenin fraction, favored nitrogen immobilization and denitrification and inhibited proteolysis and ammonification in both peatinoculated and Pseudomonas sp.-inoculated media. Alfalfa root saponins and sapogenins significantly reduced the fungal peat population, but did not affect the bacterial population. The inhibition of N mineralization in peat by saponins and by their sapogenin fraction during dry and wet cycles was mostly due to their fungistatic activity. The inhibitory effect of the sugar fraction of alfalfa roots on mineral-N accumulation in peat is mainly under moist conditions.