Characterization of Sphingomonas Species Found as Predominant Members in the Culturable Bacterial Community of a Green Pigment-Containing Sclerotium Grain from Mt. Myoko (Japan) Volcanic Ash Soil.

Abstract

A small spherical black fungal sclerotium grain from podzolic soils, which was tentatively identified as the resting body of Cenococcum graniforme, was assumed as the source of green polynuclear quinone pigments in P type humic acid (K. Kumada and H.M. Hurst, Nature 214: 631-633, 1967). To examine the presence of bacteria inside sclerotium grains collected from an Andosol profile in Mt. Myoko, central Japan, the grains were repeatedly washed, ultrasonicated and then cultured on diluted nutrient broth. The sum of recovered bacteria as colony-forming units from the wash and ultrasonicate fractions was 1.46×106 (g fresh weight)-1: 88% of the count in the wash fractions (assumably resulting from grain surface and attached soil) and 12% in the ultrasonicate (inside grain). Thirty-one bacterial strains were isolated from the ultrasonicate fraction and their 16S rDNA partial sequences were determined. The predominant group was the Alphaproteobacteria (71%), chiefly the Sphingomonas group (52%). Representative isolates of the Sphingomonas group were examined for their ability to grow on naphthalenesulfonic acids as a model compound of polycyclic aromatic hydrocarbons (PAHs) and also on several phenolic acids. None of the isolates tested utilized the model PAH but many of them used p-hydroxy benzoic, vanillic, p-coumaric and ferulic acids for growth. Based on these results, the relationship between the predominance of Sphingomonas and the chemical character of the sclerotium grain was discussed.