To investigate the effects of intraspecific competition on adaptive changes in dispersiveness, two types of long-term serial transfer experiments were performed using Escherichia coli in static cultures. One was designed to create a relatively high degree of exploitation competition for substrates among cells by transferring a bacterial population of small inoculation size with relatively frequent intervals, while the other was designed to create relatively high density-dependent mortality (i. e. resource deprivation and starvation before the next transfer) by using a larger inoculation size with less frequent intervals. While dispersiveness increased under both experimental treatments, measurements indicate that adaptation are not unique to the experimental treatments. These results suggest that competition in bacterial populations may be alleviated by the enhanced dispersiveness of highly competitive cells from densely populated areas.

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The aerophilic growth of the myxamoebae of a true slime mold, Didymium sp. strain H-1, was studied. Two pathways of oxygen uptake, the cyanide-sensitive and cyanide-insensitive pathways, existed in the myxamoebae. Superoxide anions were produced by the cyanide-insensitive respiration. The cyanide-insensitive respiration had a low affinity for oxygen and the growth yield vs. oxygen concentration was the same pattern as the respiratory activity. The growth of myxamoebae is concluded to be controlled by the activity of the cyanide-insensitive respiration. The importance of the cyanide-insensitive respiration of the myxamoebae in a microenvironment was discussed.

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Ammonia and nitrite-oxidizing bacteria contribute to nitrification, a part of the nitrogen cycle in natural environments. These bacteria are important since they decompose accumulated inorganic nitrogen compounds and toxic substances such as nitrogen oxides and consume (fix) of CO₂, a factor implicated in global warming. Nitrosomonas europaea, a chemoautotrophic ammonia-oxidizing bacterium which contributes to the first stage of nitrification has been studied in detail. It oxidizes ammonia as the sole nitrogen source of nitrite via hydroxylamine as an intermendiate. It grows under completely inorganic conditions using energy (65kcal) produced by the oxidation of ammonia and atmospheric CO₂, its sole carbon source. Its growth rate is thus quite low and no extensive biochemical studies have been conducted. This paper reviews recent studies on the ammonia-oxidizing system (ammonia and hydroxylamine oxidation) in Nitrosomonas europaea. Data obtained with two strains of Nitrosomonas including a pure isolated strain of Nitrosomonas sp. TK794 are presented.

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Quantitative regulation of nutrient uptake by unicellular microalgae (phytoplankton) is the key physiological process that governs nutrient cycling and phytoplankton population dynamics in natural waters. Kinetic models are widely used in quantitative description of uptake and growth as functions of nutrient concentration. A review of both experimental and theoretical works on nitrogen and phosphorus uptake by cultured unicellular algae is presented here. At least three different values of half saturation constants are identified depending on the time scale of analysis, while a single system for ion transport is considered. Quantitative relationship is obtained theoretically and experimentally among these different values of half saturation constants.

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