For the extensive detection of alkane-degrading bacteria, three combinations of PCR primer sets and gene probes were designed based on homologous regions within a variety of alkane hydroxylase genes registered in GenBank and examined for their availability. PCR with the primers amplified DNA fragments of expected size from all the bacterial strains used for primer design, and all of the amplified fragments gave positive results on Southern hybridization with the newly designed probes. To evaluate the availability of these primers and probes, they were applied to 74 wild-type alkane-degrading bacteria newly isolated from various environments. The primers amplified DNA fragments of expected size from all the wild-type strains, while the probes gave positive results against amplified fragments from 59 strains. The results suggest that this primer and probe system can detect most alkane-degrading bacteria, and can be applied to evaluate alkane-degradation potential in the environment.

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Ammonia-oxidizing bacteria are able to maintain a high oxidizing potential during starvation. Nitrite has a short-lasting stimulatory effect on the oxidation of ammonia after starvation when supplied simultaneously with fresh ammonium9). To examine whether nitrite-oxidizing bacteria as partners in naturally occurring nitrifying communities interfere with this stimulatory effect of nitrite, mixed culture experiments were performed in sand slurries. Following the consumption of ammonium, these mixed cultures were starved for 4 months in their own medium. After the starvation period, ammonium was supplied. In contrast to the former experiments in monocultures of Nitrosomonas europaea, no short-lasting peak in ammonium oxidation activity was observed in the presence of nitrite-oxidizing cells. When these nitrite-oxidizing cells had been pre-activated with 5 mM nitrite one week before ammonium was supplied to the starving cultures, ammonia-oxidizing activity was weakened for up to four days, depending on the culture examined. The possibility that ammonia-oxidizing cells are repressed in the presence of nitrite-oxidizing cells in natural environments such as nitrifying biofilms is discussed.

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The effect of the protozoa Tetrahymena thermophila or glass beads on the biomass of the bacterium Pseudomonas sp. strain DP-4 and metabolism of glucose in a steady state was studied in a food chain system of glucose-Pseudomonas sp. strain DP-4-T. thermophila. Glucose was added to 1.5 ml cultures in 50 ml vials at a rate of 50 μg C/vial/day. In the 1.5 ml cultures without glass beads, the bacterial biomass was ca. 450 and 26 μg C/vial when the protozoa was absent and present, respectively. The bacterial biomass with glass beads was ca. 650 and 34 μg C/vial when the protozoa was absent and present, respectively. Protozoan biomass was 7 and 20 μg C/vial without or with glass beads, respectively. Irrespective of presence of the protozoa or glass beads, the rate of consumption of glucose per vial (50 μg C/vial/day) was considered to be almost the same as the rate of CO₂ evolution per vial (45-47 μg C/vial/day). The diameter of the glass beads (50, 70 or 100 μm) had no effect on the bacterial biomass in the absence of the protozoa. While, in the presence of the protozoa, the bacterial biomass was greatest when the diameter of glass beads was just 50 μm. These results suggested that the rate of glucose consumption per unit bacterial biomass of 0.11 μg glucose-C/μg biomass-C/day was increased to 1.9 μg glucose-C/ μg biomass-C/day by protozoan predation, while the value was decreased to 0.077 μg glucose-C/μg biomass-C/day by glass beads. The significance of protozoan predation and particles for bacterial biomass and metabolic activity was discussed.

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Two large-celled bacterial species, Chromatium sp. and Macromonas sp., densely populate the mid-depth of Lake Kaiike, a small lagoon on Kamikoshiki Island, turning the water a purplish red (bacterial plate). In recent years, the Chromatium population has showed large seasonal fluctuations; maximum cell numbers in the order of 10⁶ cells ml^-1 have dropped to 10³ cells ml^-1. To examine the factor(s) disturbing the population, the profiles of two bacterial species as well as environmental factors were examined during the period June 1998 to Oct. 2001. Solar heating to raising the water temperature above 30°C as well as a proliferation of Macromonas sp. were found to have disturbed the Chromatium population.

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A nitrogen fixation gene, nifH, was amplified from mRNA of the gut microbial community of the termite Coptotermes formosanus by RT-PCR and clonally characterized. The clones were affiliated with either the anaerobe group or the pseudo-nif group of nifH, the latter of which is considered not to be involved in nitrogen fixation. No other nitrogenases were found in the gut community. Although the taxonomic identification of the relevant microorganisms is difficult to predict, the anaerobe group of the genes is critical for nitrogen fixation in this termite.

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The cellular ATP concentration of Spirulina platensis increased when cAMP was added at a low concentration of 0.02 mM. The increase in ATP accompanied a decrease of ADP and AMP. The presence of a high concentration of Na⁺ (0.22 M) remarkably intensified the effect of cAMP. A Na⁺ channel blocker, amiloride, and a Na⁺ ionophore, monensin, suppressed the cAMP-dependent increase in cellular ATP. A H⁺ ionophore, carbonyl cyanide m-clorophenylhydrazone, which inhibits the activity of F_oF₁ ATP synthase, did not affect the cAMP-dependent rise in ATP. It is suggested that cAMP stimulates the formation of ATP coupled directly with the translocation of Na⁺.

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A new cyanophage, strain S-KM1, infecting a phycoerythrin-rich Synechococcus sp., strain KFM001, was isolated from seawater of Kagoshima Bay. Transmission electron micrography of negative-stained specimens revealed that the phage isolate has an isometric head with a diameter of 83 nm and a contractile tail 166 nm in length and that it belongs to the family Cyanomyoviridae. The cyanophage was apparently virulent to the host strain KFM001 with a burst size of less than 70-80. The cyanophage may affect the population structure of the dominant picoplankton species in Kagoshima Bay.

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