Changes of bacterial population of following two conditions were studied during soil freezing seasons in the field; vertical distributions in soil, and differences among winter wheat rhizoplane, rhizosphere soil, and non-rhizosphere soil. Bacterial viable count and ATP concentration of different soil depths were related to the process of soil freezing and thawing. Viable count of rhizoplane apparently decreased in the process, while those of rhizosphere soil and non-rhizosphere soil did not.

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A method for the preparation of minute, delicate and dilute suspended organisms for scanning electron microscopy (SEM) by using of Nuclepore filter bags (NFB) is described. NFBs are easily made by welding with a heat sealer and are inert with solvents used in the preparation of specimens for SEM. The use of NFB avoids the risk of unintentional air-drying, physical damage, contamination, and loss of specimens during preparation. Specimens prepared by NFB show fine details of three-dimensional surface structure.

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Quantitative DNA-DNA hybridization and DNA base composition (mole % G+C) were applied to bacterial flora analysis in a eutrophic lake. Biochemical and morphological characterization by API 20 NE revealed 26 isolates from the eutrophic lake consisting of one major and three minor phenotypic groups. The isolates of each phenotypic group had a similar mole % G+C. DNA-DNA hybridization of these isolates showed that these phenotypic groups belonged to three genetic clusters. Two clusters were represented by each phenotypic group, but one of them included two strains phenotypically unidentified by API tests. Another cluster was consisted of two phenotypic groups and two unidentified strains. Thus, DNA analysis revealed different profile of the bacterial flora from the conventional method, adding genetic information of the constituents of bacterial community.

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Bacterial communities in epilithon on the river bed were examined at the Tamagawa River by a plate count method. Colonies developed on 1/2 PYG agar plates were classified into four groups according to the colony forming time. Incubation periods which were needed for the colony formation were between 0 and 48 hours for group A, 24 and 72 hours for group B, 120 and 168 hours for group C, and 288 and 336 hours for group D. Generic compositions and diversity indexes of the four groups were similar each other. On the other hand, positive reaction against morphological and physiological characterization (specific total activity) of these groups were quite different each other. Group A, which contains the organisms having the fastest colony forming time, had high specific total activity. On the other hand, group D, which is constituted with the bacteria having the slowest colony forming time, had lowest specific total activity. Most bacterial strains of the group A grew rapidly on the 1/2 PYG agar medium, too. However, the group D included organisms which grew both rapidly and slowly on this medium. Based on these results, the colony formation of the bacteria seemed to prescribe largely by the physiological conditions of the cells at the time when cells were placed on the agar plates.

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Inhibitory effects of products formed by heating reaction (HRP) of sugar and sugar- amino acid (glycine) on the growth, nitrite production and activities of hydroxylamine oxidase (HAO) and dehydrogenases (MDH, ICDH, GDH) of ammonia-oxidizing chemoautotrophic Nitrosomonas europaea were studied. Among the HRP of each sugar alone, HRP of pentose inhibited severely the growth and nitrite prodction, but not HAO activity. Among HRP of sugar-glycine, HRP of pentoseglycine showed a more intense inhibitory action than that of sugar alone. HAO activity was inhibited by HRP of pentose and disaccharide other than sucrose. HRP of sugar-alanine showed similar inhibition. HRP of sugar and di- and tripeptide of these amino acids also exerted similar inhibitory action. GDH activity was inhibited by HRP of sugar-glycine while ICDH and MDH activitdes were not inhibited. Similar tendency of inhibition was observed with the activity of HAO produced by Pseudomonas, which is corresponding to growth inhibition. The growth of E. coli and Bacillus, heterotrophic bacteria, however, was not influenced at all.

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Soil or terrestrial ciliates live in the water which may either cover the surfaces of litter as a thin film or fill the pores of soils. These ciliates, which may adapt to various environments from dry to wet depending on the weather, share some important roles in the natural ecosystems. Nevertheless, only a little knowledge has been available on their taxonomy and ecology. This is mainly due to the difficulty in identifying ciliate species, and to the lack of appropriate methods for detecting soil ciliates and for estimating their biomass. This review presents a list of ciliate species in straws of rice-stubbles and in soils from drained paddy fields which are considered one of the terrestrial habitats. A total of 79 species belonging 12 orders were found in the straws and soils. The number of hypotrich species (37 species; 46.8%) was remarkably greater than that of other taxa. These ciliates successively emerged as free-swimming forms when straws or soils were placed in the petri dishes containing tap water. A common adaptive trait of these ciliates may be their ability to produce resting cysts. The tests of drought resistance indicated that more than half of them remained viable in a desiccated state for 18 days. Finally, a brief discussion was made on some problems to be resolved in soil ciliate ecology.

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