Kyo Sato

Degradation and metabolism of a fungicide, 2,4,5,6-tetra-chloroisophthalonitrile (TPN) in soil

SummaryDegradation of a fungicide, 2,4,5,6-tetrachloroisophthalonitrile (TPN) in soil was studied under laboratory conditions. TPN degraded more rapidly under 60% WHC conditions than at 20%, 40% and 100% WHC, while its degradation was rapid at temperatures of 25°C-30°C, evidently due to the microbial degradation. TPN degraded mainly through dechlorination and partly a substitution reaction. The degradation products identified by gas chromatographic analyses were: 2,4,5-trichloroisophthalonitrile (abbreviated as 2,4,5-Cl3-IPN), 2,4,6-Cl3-IPN, 2,4-Cl2-lPN, 2,5-Cl2-IPN, 4-Cl-IPN, 5-Cl-IPN, IPN, 2,5,6-Cl34-(OH)-IPN and 2,5,6-Cl3-4-(OCH3)-IPN. Peaks with longer retention times than that of TPN were not identified. Tentative degradation pathways were proposed on the basis of the identified degradation products. About 90% of the bacterial strains isolated from the soil to which TPN had been added degraded TPN, suggesting enrichment of the soil with TPN-degrading bacteria.

Gram-positive bacterial flora on the root surface of wheat (Triticum aestivum L.) grown under different soil conditions

We identified 108 Gram-positive bacterial strains isolated from the root surface of wheat grown under different soil conditions. The strains were divided into four groups based on morphological and physiological characteristics, but most appeared to be coryneform. The taxonomic position of the various groups was verified by the guanine+cytosine DNA contents of the strains. In general, the ranges of these values agreed with those described for the respective taxonomic positions in the literature, with a few exceptions. With soil improvement the distribution of the various groups on the root surface changed, with the coryneform group becoming dominant. This group was further divided into five subgroups, according to cell wall components, cellulose-decomposition, and morphological characteristics, and were identified to genus level. The distribution of these subgroups on the root surface of wheat did not alter with soil improvement. The genus Arthrobacter, the dominant subgroup, predominated in every plot.

Effect of a pesticide, pentachlorophenol (PCP) on soil microflora

Although pentachlorophenol (PCP) retarded the initial increase in total viable bacteria and gram-negative bacteria in the percolated soil, populations exceeded those in the percolated soils without the addition of PCP at a later period. This seems to be a phenomenon similar to “the partial sterilization effect”. On the other hand, spore counts were continuously lower in the percolated soils when PCP had been added. Ammonification of glycine was also slightly inhibited, but nitrification of ammonium was strongly depressed by PCP. Other physicochemical changes of the percolate proceeded according to those of bacterial populations and biochemical reactions.

Effect of increasing pentachlorophenol (PCP) concentrations on bacterial populations in glycine-percolated soils

SummaryPopulation changes of several bacterial groups were compared between soils percolated with glycine and amended with different amounts of pentachlorophenol (PCP). PCP retarded the increase in total viable bacteria with increasing doses of PCP. The increase was followed by a gradual decrease, but the numbers in the soil remained at the maximum level for a short time in the presence of large amounts of PCP. The numbers of Gram-negative bacteria and PCP-tolerant bacterial cells increased dramatically, being followed by a comparable decrease, although the former was always slightly larger than the latter. PCP reduced spore counts. PCP and glycine in the percolation fluid dissipated during the percolation, but the dissipation of glycine was slowed by the presence of increased amounts of PCP. Large portions of PCP were detected in the liquid at the late stage of percolation. Changes in pH suggested biochemical reactions in the percolated soil. The changes differed according to the amount of PCP.

Interrelationships between bacterial populations on the root surface of wheat and growth of plant

Abstract The rhizosphere is the interface between plant root and soil. A major justification for studying rhizosphere microorganisms must be their influence on plants. Microorganisms in the rhizosphere soil and rhizoplane can affect plant growth either beneficially or adversely (Rovira 1965). Furthermore, as plant roots exude raw materials that feed the microbes in the rhizosphere, the microbial activity differs quantitatively and qualitatively from that in the soil beyond the influence of the root (Curl and Truelove 1986).

Fluctuations in bacterial populations on the root surface of wheat (Triticum aestivum L.) grown under different soil conditions

SummaryPopulations of several bacterial groups on the root surface of wheat and in root-free soil were investigated in volcanic ash soil and non-volcanic ash soil throughout a series of predetermined intervals. Over time, the populations changed similarly both on the root surface and in root-free soil. The numbers of total bacteria, fluorescent Pseudomonas spp., phosphate-solubilizing bacteria, and NHinf+sup4-oxidizing bacteria, were consistently lower in the plots with volcanic ash soil than with nonvolcanic ash soil, but the numbers of cellulose-decomposing bacteria were opposite to those of the other groups. Superphosphate application improved the growth of wheat in the volvanic ash soil. It did not, however, bring about any significant changes in the bacterial populations among the volcanic ash soils supplemented with three different levels of superphosphate, though there were some variations with plant age.

Comparative study of soil bacterial flora as influenced by the application of a pesticide, pentachlorophenol (PCP)

The effects of pentachlorophenol (PCP) applications on the taxonomic composition of bacterial microflora were studied in water-logged soil (WS) and in shake cultures of suspended soil (SS). PCP applications resulted in a predominancy of Gram-negative bacteria over Gram-positive species. Members of the Acinetobacter group were the most common in PCP-treated soil although a small portion of the flora were in the Pseudomonas-Alcaligenes group or belonged to the Enterobacteriaceae. Coryneform bacteria and species of the Bacillus were the dominant forms in untreated WS; however, WS cultures treated with PCP at recommended rates (2.67 gm/m2) evidenced species of Pseudomonas, Alcaligenes, Acinetobacter, and members of the Enterobacteriaceae as the predominant bacterial species. The dominance of Gram-negative bacteria in PCP-treated soil was evidenced for 3 months after application of the compound but was not evident after 17 months when PCP had dissipated. Gram-negative bacteria found in PCP-treated soil were highly tolerant of the phenol. In WS cultures coryneform bacteria were the most common although PCP tolerance was heterogenous in nature.

Relations between soil microflora and CO2 evolution upon decomposition of cellulose

SummaryThe investigation was carried out to study the relation between CO2 evolution and the changes in microflora in the case of cellulose-decomposition in soil with special attention to the heterogeneity of soil crumbs.The rates of CO2 evolution correlated with the number of Gram-negative bacteria, while the number of cellulose-decomposing microorganisms did not. The Gram-negative bacteria probably contribute directly to CO2 evolution by decomposing simple sugars produced from cellulose by cellulose-decomposing microorganisms. Both the Gram-negative bacteria and cellulose-decomposing microorganisms seemed to grow luxuriantly on the surface area of soil crumbs with added cellulose powder. Therefore, it is speculated that there is a cooperation between the Gram-negative bacteria and the cellulose-decomposing microorganisms with respect to cellulose decomposition in soil. The main locus where this reaction takes place may be the surface area of soil crumbs.

Effect of Glycine, Glutamate, and Glucose on Proliferation of PCP (Pentachlorophenol)-Degrading Microorganisms in Soil

Abstract Pentachlorophenol (PCP) had been used as both herbicide and fungicide. Although its application to paddy fields as herbicide is prohibited because of its toxicity to organisms living in water-streams, it is still used as fungicide for upland crops or timber. Its microbial degradation has been reported by many authors (Cserjesi and Johnson 1972; Watanabe and Hayashi 1972; Watanabe 1973, 1975, 1977; Kuwatsuka and Igarashi 1975; Suzuki 1983a, b; Engerhardt et al. 1986), including the degradation in soil (Watanabe and Hayashi 1972; Kuwatsuka and Igarashi 1975; Watanabe 1977). Since almost all of the PCP-degrading microorganisms isolated from soil are common species which are not nutritionally fastidious (Watanabe 1973; Suzuki 1983a, b), the microorganisms can grow in utilizing some common nutrients present in soil. Therefore, it is interesting to determine how they degrade the pesticide in the presence of common nutrients in the case of mixed populations in soil because biological relations between t...

A proposal for re-evaluating the most probable number procedure for estimating numbers of Bradyrhizobium spp.

The reliability of the most probable number (MPN) method for estimating bradyrhizobial numbers was evaluated by comparison with the plate count procedure. MPN estimates increased with time of nodulation scoring after seedling inoculation through 6 weeks of incubation. Ratios of MPN to plate counts increased as the bradyrhizobial cell suspension concentration increased. The MPN method could not detect Bradyrhizobium japonicum numbers at concentrations of 103 colony forming units (CFU) ml-1 and below. A proposal for re-evaluating MPN estimates is discussed.