We developed a method for isolation of Myxobacteria which have a particular bacteriolytic activity on other microorganisms. We collected 77 soil samples from Tohoku District (northern parts of Japan) and obtained 53 purified strains of Myxobacteria using the method. These Myxobacteria showed some interesting properties of producing protease, lytic enzymes and antibiotics.

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Change over a week period in the population composition of marine ciliates attached to solid substrata was studied. A number of 0.1mm thick Teflon and about 1mm thick microscopic glass slides were placed at depth of 0.5m in seawater at Aburatsubo Inlet, Kanagawa-ken. Heterotrophic nanoplankton (HNP), ciliated protozoa, algae and DAPI-stained bacterial cells were counted using Nomarsky and fluorescent microscope. A video camera attached to the microscope was used for identification of ciliates. The numbers of bacteria, HNP, and algal population on the substrata were much higher than those in the surrounding water. Ciliates (1200 and 2400 cells/cm² on glass and Teflon slides, respectively) appeared on the first day and seemed to feed actively on attached microorganisms. Among the dominant ciliate population (Dysteria, Aspidisca, Geleia, Litonotus, Euplotes, Holosticha and Loxophyllum), bacteriovorous ciliates attached within the first 3 days to both substrata followed by the appearance of herbivorous species. Twenty three and seventeen species of ciliates were found on Teflon and glass slides, respectively. The maximum diversity index was observed on the fourth day on both substrata. Succession of ciliate species should be due to the change in food composition despite the nature of the substrata.

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Encystment and excystment in the life cycle of a dinoflagellate Peridinium sp. B3, which was isolated from Lake Begnas in the Pokhara Valley, Nepal, were investigated by use of a clonal population. The maximum cell concentration was 3×10³ vegetative cells·ml^-1 in BL medium after about 4 weeks at 30°C. Sexual reproduction of the cells was induced after the cells in late logarithmic phase were inoculated into nitrogen and phosphorous deficient medium, and also was spontaneously induced in BL medium.
Sexual reproduction was isogamous and homothallic. The cycle was initiated by gamete formation, in which gametes were produced by binary asexual divisions of the vegetative cells. Fusing pairs were formed by the mid-ventral union of gametes. The planozygote retained two red bodies and remained motile for about 2 weeks. Two weeks after the planozygote lost motility, the zygotes enlarged and became dark in color. The theca of the planozygote split around the girdle region and the hypnozygote (cyst) was produced. The matured cysts were dormant and remained viable for at least 1 month at 10°C in darkness following maturation for 3 months at 30°C. The dark-cold treated cysts excysted synchronously when the incubation temperature was raised to 30°C. The protoplast emerged from the cyst wall by amoeboid movement. The excysted cell had two red bodies. This cell divided within 24-48 h into 2 daughter cells each with a red body.

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Vertical change of the heterotrophic bacterial community attached to particulate organic matter (POM) was studied in relation to the distribution of POM in the neritic sea of Japan. The analysis of bacterial community was performed by dividing the isolates into five groups: Vibrio (V), Pseudomonas-Alcaligenes (Ps), Acinetobacter-Moraxella (Ac), Chromogenic (C) and Gram-positive (Po) groups. The community structure of attached bacteria was quite different from that of free-living in the ambient seawater. In the water column, the community of attached bacteria showed the distinct vertical succession, which was: Ps→V→(Ps+Ac)→(Ac+C)→Ps. The attached bacteria in the layers where the decomposition of POM proceeded actively had high substrate-decomposing activity, whereas in the deeper layers with limited supply of the “fresh” POM the activity was low. These results suggest that the community of attached bacteria showed the vertical succession with the proceeding of POM decomposition from the community with a high biochemical activity to a low activity, as associated with the change of genera.

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A microorganism is as small as colloidal dimension ca. 1μm. So, it has a large specific surface area: surface area per unit mass of a microbe seems to be ca. 100, 000 times larger than that of man. This makes the microbe more sensitive to its environment. In the natural ecosystem many microbes are adsorbed on interfaces formed by various materials. In this situation the environment for the microbe is the interface formed by the material on which the microbe is adsorbed. Thus, it is very important to clarify the relation between interface and the microbe for understanding microorganisms in the natural ecosystem. However, we know little about the effect of interface on microbe. This is due to the complexity of this system: the property of the microbe as a colloidal particle is changing every moment as a result of its living activity and the property of interface is also affected by the materials produced by the living microbe.
In this review I introduce a way to investigate this complex system by clarifying, at first, the force operating between interface and microorganisms by using the term of surface and interfacial tension. Secondly, hydrophobic interaction is discussed in connection with microbial adhesion and activity, since this interaction has been noticed as one of the key factors operating at interface. Though the phenomenon in this system is very complex, the key factor controlling the interaction between interface and the microbe seems to be relatively simple. I expect that the consideration of the interaction by the physico-chemical term will become a clue to solve the complex phenomena at interface.

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