Yutaka Komai

Occurrence of Curtobacterium sp. possessing ?-cyclohexyl fatty acids in soil with zinc added

A bacterial strain, Curtobacterium sp., isolated from a soil with zinc added possessed ω-cyclohexyl fatty acids. ω-Cyclohexyl undecanoic acid made up 47% of the total fatty acids; it was the most abundant fatty acid in the strain grown in tryptone medium. 12-Methyl tetradecanoic acid (23%) and 14-methyl hexadecanoic acid (22%) were also major fatty acids. The proportion of ω-cyclohexyl undecanoic acid increased as the pH of the medium decreased and as the culture temperature increased.The bacteria grew almost normally in zinc-enriched medium, and ω-cyclohexyl undecanoic acid increased with zinc concentration. Zinc added to the medium was not abundant in the cell fraction, and the ratio of increase of zinc in the cells was not so high as in the culture medium. These results suggested that ω-cyclohexyl fatty acids are related to the zinc tolerance of the isolated strain, and that this tolerance depends on low permeability of the membrane to zinc.

Beneficial effect of hydrogen uptake ability on survival of bradyrhizobium japonicum in soil aggregate

The relationship between the hydrogen uptake ability of rhizobia and their survival in soil was examined in two kinds of experiments. Indigenous rhizobia in soil were separated by a centrifugation-sonication technique into two populations differing in their location in the soil; the inner and outer areas of the soil aggregate. Each fraction was inoculated to soybean, and the nodules formed on the plants were assayed for acetylene reduction and hydrogen evolution by gas chromatography. Relative efficiency (RE) in nitrogen fixation of each nodule was assumed to be an indication of the hydrogen uptake ability of the rhizobia which formed the nodule. When the soils were incubated at 30°C for 14 days at 60% WHC moisture content, the inner fraction showed a higher ratio in the frequency of rhizobia with a RE value above 0.8 than the outer fraction, after compared to before soil incubation, respectively. Eight strains of antibiotic-resistant Bradyrhizobium japonicum, which showed different RE values, were separa...

Studies on a red-colored soil derived from basaltic andesite of Shibayama

Abstract In the preceding papers (1, 2), the specificities of Shibayama red soil clarified by chemical and mineralogical studies were described.

Isolation of transposon Tn5-induced hydrophobic mutants of a Bradyrhizohium japonicum strain with improved competitive nodulation abilities

Abstract Hydrophobic mutants of the Bradyrhizohium japonicum strain 138NR were obtained by transposon Tn5 mutagenesis followed by replica-plating on polystyrene plates. Fifteen mutants were isolated at a frequency of 106. Gel-filtration analysis of the exopolysaccharides revealed that the hydrophobic mutants produced a significantly smaller amount of low-molecular-weight polysaccharides than the parent. Four of the isolated mutants formed a larger number of nodules on soybean (Glycine max L. Merr. cv. Tamahomare) than the parent, two were superior in symbiotic nitrogen fixation, and two were symbiotically defective on soybean. Competitive nodulation abilities of the mutants were examined by inoculating them to soybean with B. japonicum strain 123ET as a competitor and determining the nodule occupancy based on the antibiotic resistance. All the mutants tested except for the symbiotically defective ones were superior in their competitive nodulation ability to the parent strain. When inoculated 24 h before t...