Bacterial two-component signal transduction systems (TCSs) play a pivotal role in environmental adaptation. In this minireview, two TCSs in Escherichia coli are clarified: the PhoP/PhoQ system, which senses extracellular Mg²⁺ and controls the expression of the genes for adaptation to environmental Mg²⁺ deprivation (Mg²⁺ regulon); and EvgA/EvgS, a signal transduction system that activates expression of the drug efflux pump genes. Furthermore, based on the inhibition of YycF/YycG signal transduction in Bacillus subtilis, a novel strategy for developing a new class of antibacterial agents is described.

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Vibrio halioticoli is the dominant bacterial species in the gut of abalone, Haliotis discus hannai. The bacterium may contribute to the digestion of seaweed, and form a symbiotic association with the host. However, the process by which the bacterium colonizes the gut of abalone is unknown and intriguing given the non-motile nature of V. halioticoli. To clarify the colonization process, the distribution of the bacterium in seawater, as well as the fecal material and diet of abalone was investigated at an abalone farm. Viable bacterial counts of V. halioticoli were determined in each sample using a colony hybridization technique specifically designed for the bacterium. The count in seawater and culture seawater was 3 CFU/ml. The number of V. halioticoli in a diatom bed used as a diet for juvenile abalone was 7.9×10 ² CFU/g. Fractionation of the diatom bed sample using 0.2 and 8.0-μm filters indicated that the viable count was higher in the attached fraction (3.4×10 ² CFU/g; >8.0 μm) than in free-living fraction (76 CFU/g; 0.2 μm-8.0 μm). Furthermore, viable V. halioticoli was estimated to be 3.6×10³ CFU/g in the fecal material of juvenile abalone which had ingested diatoms, as compared to 1.2×10⁵ CFU/g in that of juveniles fed on artificial diet. These results suggest that V. halioticoli cells in seawater and/or on diatoms contribute to the colonization of the gut in abalone.

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In highly eutrophicated Tokyo Bay, anoxic, sulfide-containing bottom water is formed in warm stagnant seasons. It seems to develop especially in the northeast area where there are many large holes made by dredging to collect sand in addition to navigation channels. At such dredged sites, the seasonal variation in the rate of sulfate reduction in sediment was examined by a radiotracer method together with various environmental factors for two years and the results were compared with those obtained at a site on the natural sea floor. The rate of sulfate reduction was much higher at the dredged sites than on the natural sea floor. The dissolved oxygen concentration in bottom water and sulfate concentration in the sediment layer were lower, and the density of sulfate-reducing bacteria and acid-volatile sulfides were higher at the dredged sites than the natural floor site. However, there was no significant correlation between the sulfate reduction rate and any of the environmental factors examined (temperature, ignition loss, DO in bottom water and density of sulfate-reducing bacteria). The rate on an area basis seemed to fluctuate in a similar pattern to the change of chlorophyll a in the water column. The addition of seston mainly composed of diatoms to the sediment sample greatly stimulated sulfate reduction in contrast to the addition of lactate. Sulfate reduction at these sites might be controlled by the supply of organic substrates especially those of algal origin.

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In the aquatic environment, chemotaxis is one of the most important mechanisms of association between bacteria and other living biota. To investigate the mechanism of the chemotactic movement of Vibrio cholerae 0139 toward blue-green algae (BGA), the homogenates of four BGA species, Anabaena spp., A. variabilis, Nostoc spp. and Hapalosiphon spp., were examined by chemotaxis capillary assay. The assay revealed that V. cholerae 0139 swims toward the BGA with the highest chemotactic response observed in a 4% solution of Anabaena spp. homogenate. The components of the mucilaginous sheath involved in this chemotactic response were examined. Major components were tested in a chemotaxis assay to determine the attractants present. A number of mucilaginous sheath-associated compounds, in particular free amino acids and carbohydrates, acted as chemoattractants for V. cholerae 0139. Importantly, only when these attractants were combined into a single mixture were levels of chemotactic activity similar to those of Anabaena spp. It was revealed that 25°C and 1.7% salinity favored the chemotactic motility toward the homogenates of BGA. V. cholerae 01 was also attracted to homogenates of Anabaena spp.

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The distribution of a newly cloned oxytetracycline (OTC) resistance determinant, Tet 34, was examined among bacterial strains isolated from diseased fish. We analyzed 33 OTC-resistant strains isolated from 1998 to 2000 in Kagawa Prefecture. Tet 34 was detected in 3 of the strains, which were grouped in the genus Vibrio. Minimum inhibitory concentrations (MICs) of the 3 strains were higher than 500 μg/ml in the presence of MgCl₂, and 125 or 250 μg/ml in its absence. Tet 34 was found in chromosomal DNA in all positive strains. Polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis of 16S rDNA revealed the 3 strains to have the same migration profiles. The sequences of their PCR products were also identical, suggesting that the species were the same. It was concluded that Tet 34 has been present since at least 1998, and the determinant occurs only in Vibrio species.

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Acrylic cylinders were packed with 2 kg of soil and carbonyl sulfide (COS) gas (100 μl l^-1) was introduced to the columns at a rate of 0.5 l min^-1. The COS concentration of the outlet gas reached equilibrium at 50 μl l^-1 within a few minutes in the cylinder packed with sandy soil but was less than the detection limit for 24 h in the cylinder with Andosol. Sterilized soils did not show any decrease in COS. The amount of sulfate in the sandy soil increased on the introduction of COS for 24 h, and this suggested that approximately 48% of the sulfur moieties of COS were converted to sulfate by the microbial activity. Batchwise experiments adding high concentrations of COS such as 8000 μl l^-1 into sealed flasks also showed a rapid degradation of COS. Batchwise experiments with Andosol were performed to clarify the relationship between the activity to degrade COS and temperature, soil water content or microbial biomass. COS-degrading activity rose with the increase in temperature and fell with the increase in soil water content. The rate constant and microbial biomass had a good correlation (correlation coefficient=0.79). Our results indicate that COS-degrading microorganisms are widely distributed in soils, and serve as a possible sink of COS in natural environments.

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Activation of a 40 kDa protein kinase in Dunaliella tertiolecta was detected by in-gel kinase assay when the cells were subjected to various forms of stress, such as heat shock, acidic stress and H₂O₂. The substrate specificity of the 40 kDa kinase resembles that of HAP kinase (high osmotic pressure-activated protein kinase). An anti-phosphotyrosine monoclonal antibody did not co-precipitate with the 40 kDa kinase in the cell extracts of Dunaliella subjected to stress. Treatment of Dunaliella cells with mastoparan or AlF₄^-, trimeric G-protein activators, stimulated another protein kinase with a relative molecular mass of 46 kDa. This protein kinase has a different substrate specificity from that of HAP kinase and the stress-activated 40 kDa kinase. These results suggest that the stress-activated 40 kDa kinase is closely related to HAP kinase and that the 46 kDa kinase is associated with a putative trimeric G-protein.

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Aquificales, a thermophilic bacterium of the deepest-branching lineage of the domain Bacteria produced virus-like particles (VLPs). Mature VLPs resided in 6.5±4.4% (n=341) of bacterial cells. A count of the free particles in water from geothermal hot spring showed high abundance (1.41±1.70×10⁷ VLP/ml, n=12). The molecular mass of the VLP-encapsulated DNA was 406.4±10.1 kb (n=13).

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The bactericidal effects of "Virus-like particles" ("ST-VLPs") derived from a sulphur-turf microbial mat consisting of the Aquificales bacterium, were examined using Escherichia coli AB1157 and Bacillus subtilis PS9 as recipients. The recipient population was reduced by up to one order of magnitude with transduction frequencies of between 10^-3 and 10^-4 per particle. Broad host range and xenotrophic behaviour imply that "ST-VLPs" do not fit the current concept of a "virus" with a narrow host range. Such novel VLPs would control the bacterial population, and genetically enhance biodiversity.

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