Bacterial production of cytokinin-type and auxin-type plant hormones was investigated with 328 strains isolated from seawater, sediment and various alga samples. Proportions of the producers among heterotrophic marine bacteria were quite high, 10-80%, showing higher rate in the samples from multicellular algae and sediments than those from unicellular algae and seawater. The amount of auxin, indole-3-acetic acid, produced in the culture was mostly in the level of 10^-7mol/l, which was about 100 fold greater than that of cytokinin compounds. Marine Gram-negative bacteria capable of the cytokinin and the auxin production were classified in 9 groups by a combination of key taxonomic characters. In the alga samples, there were some differences in taxonomic groups between cytokinin- and auxin-producers, but as a whole the ability of plant hormone production tended to distribute in various genera of marine bacteria.

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A scanning electron microscopic examination of forest soil-filtrate (0.4μm) revealed many small square cells with a size of about 0.3μm. Laboratory cultivation of the square bacteria seemed to be possible only in the presence of another soil bacterium isolated from the same site. Most square cells were shown to be attached to the surface of this (curved/spiral) bacterium.

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Seasonal fluctuations in the total and viable numbers of bacteria were investigated at Miidera-oki in Lake Biwa and at Kunijima in the Yodo River in Japan. Totoal bacteria estimated by the 4'6-diamidino-2-phenylindole (DAPI) direct count method varied in the range of 1.3×10⁶-1. 4×10⁷ cells·ml^-1 in Lake Biwa and 2.5×10⁶-4.0×10⁷ cells·ml^-1 in the Yodo River respcetively. The viable bacteria, HNB, which were estimated by the plate count method with agar medium containing a high concentration of organic nutrients were 3.3×10-3.7×10³ CFU (colony-forming units)·ml^-1 in Lake Biwa and 1.3×10⁴-7.2×10⁴ CFU·ml^-1 in the Yodo River. The viable bacteria, LNB, which were estimated by the same method with agar medium containing a low concentration of organic nutrients were 1.7×10³-1.0×10⁵ CFU·ml^-1 in Lake Biwa and 7.1×10⁴-1.4×10⁶ CFU·ml^-1 in the Yodo River respectively. The number of LNB as a percentage of the number of the total bacteria was 2.5% at most in Lake Biwa but 27.4% in the Yodo River. The viable bacteria tended to be more abundant in the Yodo River, which was eutrophic, than in Lake Biwa. The total number of bacteria was not correlated with the biochemical oxygen demand (BOD) or potassium permanganate consumption (KMnO₄-C) at either site. However, the number of LNB was a negatively correlated with the BOD in Lake Biwa and positively so in the Yodo River. In both sites, the numbers of LNB were correlated with KMnO₄-C.

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