The effect of moderate UV-irradiation (45J/m²) on species diversity of asporogenic heterotrophic bacterial isolates from paddy field soil was studied. Although the isolates from irradiated Petri dishes had less pronounced hydrolytic abilities and eutrophs were less numerous, irradiation did not result in specific selection of UV-resistant bacteria. Species diversity indices were higher for the set of isolates from irradiated dishes. This can be due to the fact that the number of cells inoculated onto irradiated dishes was about one hundred higher than onto control dishes; there may be a greater chance for soil bacteria of minor groups to form isolated colonies on irradiated dishes.

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Methanogenic sludge was acclimatized to butyrate as a sole carbon source and methane production from the sludge was traced. Two peaks of methane production were observed. Peak I was shown to originate from the syntrophic metabolism of butyrate degraders and hydrogen-utilizing methanogens, and peak II by aceticlastic methanogens or from syntrophic methabolism of acetate degraders and hydrogen-utilizing methanogens. Morphological and physiological characters of the strain BHM-1, a hydrogen-utilizing methanogen isolated from the methane sludge, as well as its metabolic relationship(s) with butyrate degrader(s) were investigated. The strain was identified as Methanobacterium formicicum. Butyrate was converted to methane by a colony composed of both butyrate degraders and strain BHM-1. Therefore, it was concluded that syntrophic relationship existed between both butyrate degraders and strain BHM-1 in cell level (interspecies hydrogen transfer).

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