Tomoyuki Namihira

Antibiotics production by an actinomycete isolated from the termite gut.

As well as the search for new antibiotics, a new resource or strains for the known antibiotics is also important. Microbial symbionts in the gut of termites could be regarded as one of the feasible resource for such purpose. In this study, antibiotic‐producing actinomycetes were screened from symbionts of the termite gut. 16SrRNA sequence analysis for the 10 isolates revealed that they belong to actinomycetes such as Streptomyces sp., Kitasatospora sp., and Mycobacterium sp. A culture broth from one of the isolate, namely strain CA1, belonging to the genera Streptomyces exhibited antagonistic activity against actinomycetes (Micrococcus spp.), gram‐positive bacteria (Bacillus spp.), and yeast (Candida spp.). The structures of 2 compounds isolated from the culture broth of the strain CA1 were identified as those of actinomycin X2 and its analog, D. This study is the first to report that some symbionts of the termite gut are antibiotic‐producing actinomycetes, and suggest that the termite gut is a feasible resource for bioprospecting. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of nitrogen fertilization on tropical‐grass silage assessed by ensiling process monitoring using chemical and microbial community analyses

Aims:  Utilization of silage in livestock farming is expected to increase in developing countries in the tropical and subtropical parts of the world. The aim of this study was to investigate the influence of nitrogen fertilization on the chemical composition of herbage, ensiling process and silage quality, and to contribute to the improvement of tropical‐grass silage preparation.

Stereospecific degradation of phenylsuccinate by actinomycetes.

Racemic phenylsuccinate was stereospecifically degraded by the actinomycetes PS9 and PS17 isolated from soil obtained from Okinawa Island, Japan. Strain PS9, identified as a Citricoccus sp., preferentially degraded the R-form, while strain PS17, identified as a Microbacterium sp., preferentially degraded the S-form of phenylsuccinate. Analysis of the culture broths of these species with phenylsuccinate as the sole carbon source revealed that benzoic acid was produced as a metabolic intermediate. Benzoic acid was further degraded by strain PS9 with m- and/or p-hydroxybenzoic acid but not o-hydroxybenzoic acid as possible intermediates.

Degradation of oil tank sludge using long-chain alkane-degrading bacteria

Bacteria degrading a very long-chain alkane, n-tetracosane, were isolated from enrichment culture of soil in Okinawa. Phylogenetic analysis of their16S rRNA sequences revealed that they belong to classes Gammaproteobacteria and Actinomycetes. Three isolates belonging to the genera Acinetobacter sp., Pseudomonas sp., and Gordonia sp. showed a stable growth on n-tetracosane and had a wide range of assimilation of aliphatic hydrocarbons from C12 to C30, while not on alkanes shorter than C8. Of the isolates, Gordonia sp. degraded oil tank sludge hydrocarbons efficiently by solving the sludge in a hydrophobic solvent, while Acinetobacter sp. showed little degradation, possibly due to the difference in the mechanism of hydrophobic substrate incorporation between proteobacteria and actinobacteria. The data suggested that non-heme di-iron monooxygenases of the AlkB-type, not bacterial CYP153 type cytochrome P450 alkane hydroxylase, was involved in the alkane degradation.

Application of random amplified polymorphic DNA (RAPD) analysis coupled with microchip electrophoresis for high-resolution identification of Monascus strains.

Monascus fungi are commonly used for a variety of food products in Asia, and are also known to produce some biologically active compounds. Since the use of Monascus is expected to increase in food industries, strain-level identification and management of Monascus will be needed in the near future. In the present study, random amplified polymorphic DNA (RAPD) analysis coupled with microchip electrophoresis was applied for this purpose. Evaluations of the analysis stability revealed that reproducible results could be obtained, although template DNA fragmentation could influence the resulting RAPD pattern. RAPD analysis using 15 Monascus strains consisting of four species, M. ruber, M. pilosus, M. purpureus, and M. kaoliang showed that each strain generated a unique RAPD pattern, which allows strain-level identification of Monascus. In addition, the phylogenetic tree constructed from RAPD patterns reflected M. ruber–M. pilosus and M. purpureus–M. kaoliang clusters inferred from both ITS and β-tubulin gene sequences, which indicated that the RAPD pattern could reflect their phylogenetic traits to a certain extent. On the other hand, RAPD analysis did not support the monophyletic clustering of the four Monascus species used in this study, which suggests the necessity of reexamination of species boundaries in Monascus.

Biodegradation of thiodiglycol, a hydrolyzate of the chemical weapon Yperite, by benzothiophene-desulfurizing bacteria

Microbial degradation of thiodiglycol (bis(2-hydroxyethyl)sulfide, TDG) with petroleum-desulfurizing soil bacteria was examined. Among the bacteria tested, several strains belonging to the genera Rhodococcus and Gordonia grew on TDG as the sole sulfur source. The selected strain Rhodococcus sp. strain T09, which was re-identified as R. jostii, showed TDG degradation activity only when grown in the presence of TDG as the sole sulfur source. Repeat batch degradation of TDG by using strain T09 could be continued for over 50h, with a slight loss of activity.