Yoko Ikunaga

Thirteen novel deoxynivalenol‐degrading bacteria are classified within two genera with distinct degradation mechanisms

The mycotoxin deoxynivalenol (DON), a secondary metabolite produced by species of the plant pathogen Fusarium, causes serious problems in cereal crop production because of its toxicity towards humans and livestock. A biological approach for the degradation of DON using a DON-degrading bacterium (DDB) appears to be promising, although information about DDBs is limited. We isolated 13 aerobic DDBs from a variety of environmental samples, including field soils and wheat leaves. Of these 13 strains, nine belonged to the Gram-positive genus Nocardioides and other four to the Gram-negative genus Devosia. The degradation phenotypes of the two Gram types were clearly different; all washed cells of the 13 strains degraded 100 μg mL(-1) DON to below the detection limit (0.5 μg mL(-1)), but the conditions inducing the DON-degrading activities differed between the two Gram types. The HPLC profiles of the DON metabolites were also distinct between the two genera, although all strains produced 3-epi-deoxynivalenol. The Gram-positive strains showed DON assimilation in media containing DON as a carbon source, whereas the Gram-negatives did not. Our results suggest that aerobic DDBs are distributed within at least two phylogenetically restricted genera, suggesting independent evolution of the DON-degradation mechanisms.

Combined Analyses of Bacterial, Fungal and Nematode Communities in Andosolic Agricultural Soils in Japan

We simultaneously examined the bacteria, fungi and nematode communities in Andosols from four agro-geographical sites in Japan using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and statistical analyses to test the effects of environmental factors including soil properties on these communities depending on geographical sites. Statistical analyses such as Principal component analysis (PCA) and Redundancy analysis (RDA) revealed that the compositions of the three soil biota communities were strongly affected by geographical sites, which were in turn strongly associated with soil characteristics such as total C (TC), total N (TN), C/N ratio and annual mean soil temperature (ST). In particular, the TC, TN and C/N ratio had stronger effects on bacterial and fungal communities than on the nematode community. Additionally, two-way cluster analysis using the combined DGGE profile also indicated that all soil samples were classified into four clusters corresponding to the four sites, showing high site specificity of soil samples, and all DNA bands were classified into four clusters, showing the coexistence of specific DGGE bands of bacteria, fungi and nematodes in Andosol fields. The results of this study suggest that geography relative to soil properties has a simultaneous impact on soil microbial and nematode community compositions. This is the first combined profile analysis of bacteria, fungi and nematodes at different sites with agricultural Andosols.

Degradation profiles of branched nonylphenol isomers by Sphingobium amiense and Sphingomonas cloacae

Abstract Biodegradation activity of branched nonylphenols (BNPs) by Sphingobium amiense strain YTT and Sphingomonas cloacae strain S-3T was examined. High-resolution GC-MS was used to separate five isomer groups from the commercial BNP mixture. In the time course experiments of BNP degradation, the isomers with alpha-dimethyl and those with α-methyl, α-ethyl configurations were rapidly degraded by Sphingobium amiense strain YTT, while those with highly branched chains were broken down less efficiently. In contrast, Sphingomonas cloacae strain S-3T degraded all the isomers of the BNP groups at similar rates. The utilization and degradation of 4-n-alkylphenols (C3 to C9) and 8 phenolic acids were also tested with the strains. The results suggested that Sphingomonas cloacae strain S-3T displays a catabolic activity possesses the catabolism specific of branched alkylphenols, while Sphingobium amiense strain YTT is a versatile organism capable of utilizing a wide range of phenolic compounds including phenolic acids, and of degrading 4-n-alkylphenols and a limited range of BNPs.