A study of occurrence and distribution of cellular slime molds (CSM) in Mt. Fuji was carried out. Soil samples were collected from 3 stations, located in subalpine-alpine zone. Dictyostelium mucoroides complex, D. purpureum, Polysphondylium violaceum and P. pallidum were isolated. Number of species, absolute density and sample frequency of CSM decreased with increasing elevation. Correlation between the environmental conditions and occurrence of CSM was also discussed.

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Effect of solid particles on transfer of plasmid R100-1 from Escherichia coli LC102 to a rifampicin-resistant mutant of E. coli DHl was investigated using nutritionally-rich (L medium) and -poor medium (supernatant of a mixed liquor). Plasmid transfer was most significantly inhibited in the presence of bentonite. The addition of 2g·l^-1 bentonite decreased the specific rate of transcon-jugant increase in mating to one ninetieth in the former medium, and one twenty-third in the latter. Activated sludge decreased the rates to one third and one fifth, respectively, whereas sterilized activated sludge did not affect the rates.

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Grazing impacts of cladoceran Simocephalus vetulus population on phytoplankton standing crop were evaluated from the rates of phytoplankton biomass decrease and of organic matter sedimentation during a period between succesive sampling days in four experimental enclosures. Specific grazing rates of animal population estimated from the incorporation rates of ¹⁴C labelled algae were correlated with a regression coefficient smaller than 1 with the specific decrease rates of algal biomass and particulate organic carbon in the enclosures. Examination of the budget of organic carbon in the enclosures demonstrated pronounced temporal changes in the proportion of algal biomass increase, sedimentation loss and grazing loss in the net production of phytoplankton. In the initial phase of the experiment, algal increase accounted for 25-80% of the net production, while sedimentation loss for 19-68% and grazing loss for only 0.4-2%. Increasing animal grazing pressure and sedimentation loss after the mid-period of the experiment, which accounted for the consumption of organic matter in 176-418% and 76-170% of the algal net production, were identified as largely responsible for the pronounced decreases of phytoplankton biomass in the enclosures.

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Thai (Munoh and Kab Daeng), Japanese (Tomikura and Sagata) and Ghanaian (Ada) soils were analyzed for iron and sulfur bacteria to study their contribution to the formation of acidity in these soils. Acid sulfate potentiality was also tested for the soils (Sagata and Ada). High numbers of iron bacteria (>10⁶) and sulfur bacteria (>10⁵) were found in Tomikura and Kab Daeng soils, respectively. In addition to the high iron and sulfur bacterial numbers, these soils have high sulfate contents and high acidity (<pH 4). These properties qualify them as acid sulfate soils. In addition, Kab Daeng soil has high organic matter content and is regarded as a peat/acid sulfate soil. Munoh soil has also been classified as an acid sulfate soil since it also shows the presence of enough iron and sulfur bacteria coupled with low pH. Sagata soil has been classified as a typical potential acid sulfate soil because its pH drops sharply from 5.44 to 3.21 within 30 days of incubation. Ada soil is regarded as neither an acid sulfate soil nor a potential one, since it requires as long as 60 days for its pH to drop from 5.46 to 4.65.

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Intraspecific crossing, zygote germination and production of F₁ progenies of heterothallic strains of Gonium pectorale isolated from Tibet, Nepal and the Ryukyu Islands (Japan) were carried out. The results were compared with similarity coefficients in isozyme pattern for each cross. It was revealed that the strains from Nepal and the Ryukyu Islands which had high sexual affinity for each other had high similarity coefficients (0.80-1.00 and 0.60-0.80), while Tibetan strains which had low sexual affinity with the strains from the other areas had low similarity coefficients below 0.60 in most crosses with them. It is possible that Tibetan strains are isolated by mountain barrier and have developed a different feature in their gene from the strains of the other strains. There was a decreasing tendency in gametic compatibility and in the ability to produce F₁ progenies during routine culture maintenance. Ecological or evolutional meanings of the alteration of sex competence were discussed.

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Isozyme analysis of F₁ progenies obtained from intra- and intergroup crosses of Tibet-Nepal, Nepal-Nepal and Ryukyu Islands-Ryukyu Islands were carried out by polyacrylamide gel electrophoretic technique. Five isozyme systems, viz., malate dehydrogenase (MDH), glutamate dehydrogenase (GDH), octanol dehydrogenase (ODH), tetrazolium oxidase (TO) and malic enzyme (ME) were employed. Isozyme patterns of plus F₁ progenies obtained from the intergroup crosses of Tibet-Nepal strains were identical to plus mating type of parents. The plus or minus progenies obtained from the intragroup crosses of Nepal or the Ryukyu Islands strains followed isozyme pattern of plus or minus mating type of parent, respectively, in GDH, ODH and ME.

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