Changes in cell number and cellular morphology of Alteromonas sp., a nonobligate bacterial predator, and two types of bacterial prey, Moraxella sp. and Micrococcus sp., were investigated in a mixed incubation prepared with sterilized artificial seawater (10⁵-10⁶ viable cells/ml). A marked decrease was observed in the number of bacterial predator when the predator was incubated in the absence of prey cells for 60 days, while a relatively small decrease in the number of predator was found when the prey cells were present. Thus, the prey cells allowed the predator to maintain its number, but did not allow an increase in number.
Microscopic observation showed that the predator attached to the prey cells and lysed them. The lysate from the prey cells was available as a nutrient to the predator and to the prey species examined. The lysate nutrients present in the vicinity of the predator probably contribute to the recovery of the prey number. The predator was able to produce plaques during growth on double-layer agar plates containing a high density of prey cells (10⁸-10⁹ viable cells/ml). Furthermore, the turbidity of the mixture of predator and prey (10⁷-10⁸ viable cells/ml) decreased drastically. These results suggested that a high density of prey cells in the vicinity of the predator was necessary for appreciable lysis of the prey cells.
In the environmental condition, accumulated particulate organic matter and biofilms of solid matter in seawater would be colonized by potential prey bacteria, and the prey bacteria in turn would be lysed during attack by the predator bacterium.

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To study the effects of river flooding on vesicular-arbuscular mycorrhizae (VAM), VAM infection of plants was examined at a fluvial bar in the middle reach of the Ohta River in Hiroshima Prefecture, Japan. Among 23 plant species belonging to 11 families collected in spring and early summer 1993, 17 species showed VAM with arbuscules. The relation between VAM infection and plants' growth stages was investigated in the annual legume Kummerowia striata. VAM infection was observed early in seedlings that had few leaves. Prolonged flooding in the 1993 summer season severely destroyed the vegetation in the study site. However, most of the plants survived the flooding, and those which germinated afterward showed VAM infection. Spores of VAM fungi were found not only in the soils of areas with good vegetation cover but also in the soils of gravelly areas without vegetation. However, spore density and infection level tended to be lower in severely eroded sites.

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Hydrogen sulfide, methanethiol, dimethyl sulfide and dimethyl disulfide are famous sulfur-containing offensive odor substances from sewage treatment facilities and night soil treatment facilities. In these facilities, deodorization methods are usually chemical absorption with NaOCl and adsorption with activated carbon, but the biological deodorization in sewage treatment facilities or night soil treatment facilities has been proved to be economical and efficient. In this mini review, the authors describe the study of the biological deodorization for sulfur-containing offensive odor and recently reported sulfur-oxidizing bacteria on hydrogen sulfide or methanethiol and so on, and their application to the biological deodorization for sulfur-containing offensive odor substances in sewage treatment facilities or night soil treatment facilities.

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CO₂ accumulation as a factor of global warming is requiring attention. Obligate chemoautotrophic bacteria grow independently of organic conditions with energy from the oxidation of reduced inorganic compounds and CO₂ from the atmosphere as sole carbon sources. Chemoautotrophic bacteria consume (fix) CO₂, and assimilate CO₂ via the reductive pentose phosphate cycle (Calvin cycle). CO₂ assimilation via the reductive tricarboxylic acid cycle (TCA cycle) occurs particularly in thermophilic hydrogen-oxidizing bacteria. This paper reviews studies on the tricarboxylic acid cycle in relation to CO₂ fixation reactions of chemoautotrophic bacteria, especially nitrifying bacteria.
Nitrifying bacteria promote nitrification, a stage in the nitrogen cycle. Ammonia-oxidizing bacteria (Nitrosomonas) oxidize ammonia as the sole nitrogen source of nitrite, and nitrite-oxidizing bacteria (Nitrobacter) oxidize nitrite as the sole nitrogen source of nitrate. Both bacteria fix CO₂ mainly via the Calvin cycle in which ribulose 1, 5-bisphosphate carboxylase/oxygenase (RuBisCO) is a key enzyme. Less CO₂ is assimilated by the phosphoenolpyruvate carboxylase pathway. The TCA cycle of nitrifying bacteria was studied and CO₂ assimilation was clarified in greater detail.

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