The volatile antifungal substances produced by bacteria were researched by the double Petri-dish assay. The double Petri-dish was composed of an inner small dish inoculated with a microbial strain as a test organism and a larger Petri-dish containing another microbial strain culture previously grown on agar medium as a producing organism. In this study, 17 bacterial strains, 2 actinomycetes strains, 3 yeast strains and 5 fungal strains were used as volatile substance-producing organisms and its test organisms. In most cases, the growth of fungi as test organism was delayed or inhibited completely when a bacterium had been cultured in the large dish as the producer except lactic acid bacteria. In the assay system, producer and test strains are communicated through the gas phase only. The delay or inhibition of the growth of fungi can be presumed as a result caused by volatile substances produced by the producer bacteria

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It was previously reported in the results of the double Petri-dish assay that the growth of Aspergillus niger inoculated in a small dish was inhibited in a large Petri dish in which Serratia marcescens had been previously grown
Volatile antifungal substances emitted by Serratia marcescens were collected and identified using the gas chromatographic-mass spectrometer Volatile substance was absorbed to hydrochloric acid, and then dried by lyophilization. The residue was dissolved with a NaOH solution, and was analyzed with 28% Pennwalt 223+4% KOH column. Ammonia, aminoethane and trimethylamine were identified by mass spectra of electric ionization and of chemical ionization with methane. The gases of these amines repressed the growth of Aspergillus niger.

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Little is known about factors affecting plasmid maintenance in natural populations of bacteria. To study the effects of limitation of carbon and energy sources on plasmid maintenance, the fate of R100-1 and RSF2124 plasmids in model populations of Escherichia coli was investigated under nutrient-poor and anaerobic conditions. Nutrient-poor and anaerobic conditions adversely affected the maintenance of the plasmids. In batch culture experiments the plasmid loss was observed during the logarithmic phase of growth. Continuous culture experiments showed that nutrient-poor and anaerobic conditions strongly decreased the maintenance of plasmid-carrying populations under the competition with plasmid-free segregants.

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Soil microbial biomass was estimated in the burned and unburned Japanese red pine forests by the chloroform fumigation-incubation method. Along with this study numbers of some microbial groups (fungal spores, actinomycetes, total bacteria, gram-negative bacteria and bacterial spores) were investigated in the same soils by dilution plate count technique.
Microbial biomass-C in the 0-2cm soil layer at the burned site at Nenoura fluctuated from month to month during the period from February, 1986 to July, 1987 (34-51 months after fire) in the range from 74 2 to 134.9mg/100g dry soil, relatively low during the period from December to April and maximal in October, 1986 and June, 1987. Microbial biomass in the 0-2cm soils at the burned sites at Tennoh (4 months after fire) and Norosan (80 months after fire) and the unburned site at Ato were almost the same level as that at the burned site at Nenoura. In contrast to the relatively small fluctuations of biomass, the numbers of microorganisms, especially those of total and gram-negative bacteria, fluctuated extensively from month to month. The greater numbers of total and gram-negative bacteria appeared in October-December in the 0-2cm soil layer at the burned site and in the FH and 0-2cm soil layer at the unburned site. The numbers of all microbial groups essentially decreased in August to early-September.

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Intercalibration for counting planktonic bacteria by the acridine orange direct count (AODC) method was made among ten investigators of seven laboratories in Japan. The first calibration was made for one freshwater and two seawater samples sent to seven investigators belonging to five laboratories. Each investigator estimated bacterial abundance in these samples by the AODC method according to routine procedures of each laboratory. For the freshwater sample the estimates differed by a factor of 2.3 [coefficient of variation (CV), 36%], while for the seawater samples they varied greatly by factors of 4.0 and 11 (CV's, 46 and 94%). In the second calibration nine investigators counted bacteria on the same AODC slides under the same optical condition. The estimates of nine investigators for three freshwater samples differed by factors of 1.8-2.5 (CV's, 24-29%), while for a seawater sample they differed by a factor of 17 (CV, 89%). Sampling error associated with contagious distribution of bacteria on a filter, and difference in the criterion for discriminating bacteria from nonbacterial particles were considered to be possible sources of variation in counting bacteria.

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An enrichment culture of soil ammonia oxidizing bacteria was filtrated through a 2.0μm membrane filter (Nuclepore) to remove soil particles and filtrates were transferred to a fresh medium for the enrichment. An addition of antibiotics such as tetracycline and ampicillin and filtration through a 0.8μm membrane filter were useful to decrease contamitants. Using a higher enrichment culture colonies of ammonia oxidizing bacteria (300-600μm in diameter) were obtained on GELRITE-solidified plates. Cells picked up from the colony by means of capillary tubes were grown on a liquid media and produced nitrite from ammonia but did not show heterotrophic growth. Such isolation of ammonia oxidizing bacteria in culture using GELRITE-solidified plate was accomplished with comparative ease.

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