Many aromatic compounds are toxic when supplied at concentrations employed in most growth media. This effect was demonstrated when rhizobia and agrobacteria were grown in auxanographic plates in which cells were seeded in agar and exposed to a gentle gradient of substrate concentration. An auxanographic nutritional survey with representative strains revealed that Rhizobium japonicum and cowpea Rhizobium sp. could utilize a relatively large proportion of the aromatic and hydroaromatic compounds tested; Rhizobium leguminosarum, Rhizobium trifolii and Agrobacterium species displayed intermediate nutritional versatility; Rhizobium meliloti was relatively fastidious. The hydroaromatics quinate and shikimate were not toxic. Most of the strains examined grew at the expense of one or both of these substrates. Quinate was metabolized via protocatechuate and 3-oxoadipate. All of the strains examined were able to grow at the expense of protocatechuate and therefore must contain six structural genes for the enzymes required to convert this aromatic compound to common intermediary metabolites. Conservation of pathways for aromatic catabolism against a background of wide evolutionary divergence among the Rhizobiaceae suggests that pressures for selection of the traits were exerted throughout the evolutionary history of the organisms. A probable selective pressure is competition for nutrients in the soil. In addition, the ability of agrobacteria and rhizobia to respond to aromatic compounds may have selective value in bacterial-plant interactions.
A virulent strain of Legionella pneumophila was inoculated into an enclosed system supplied with unsterilized water from a domestic hot water supply. Growth of bacteria was monitored over 10 weeks. An increase in the number of organisms other than legionellas occurred but few amoebae were observed and none could be cultured. Viable counts of L. pneumophila in the circulation fluid decreased slightly. However, particles of debris which accumulated in the apparatus and which were stained by the indirect fluorescent antibody technique were found to be almost totally composed of L. pneumophila. On dismantling the apparatus Legionella was isolated in moderately high numbers from several different types of surfaces, particularly natural rubber and silicone.
Normalized specific growth rates of cultures of the yeast Rhodotorula rubra apparently indicate the activity of a growth control mechanism, when growth is perturbed with low concentrations of a toxic inhibitor (cadmium). Data from a number of experiments, in which different cadmium concentrations were used, indicate non-linear growth control dynamics and some features of a model structure, but do not permit it to be defined. Interpretation of the oscillatory behaviour as the response of a control mechanism to perturbation suggests that inhibition of mean growth rates, indicated by a threshold on dose-response curves, is due to overloading of the control mechanism or 'saturation'. Hormesis, the tendency of subinhibitory levels of typically toxic agents to stimulate growth, is a consequence of transient or sustained overcorrections by the control mechanism to low levels of an inhibitory stimulus.
Free-living cells of the fast-growing cowpea Rhizobium NGR234 were able to grow on a variety of carbon substrates at growth rates varying from 2.5 h on glucose or fumarate to 15.6 h on p-hydroxybenzoate. Free-living cells constitutively oxidized glucose, glutamate and aspartate but were inducible for all the other systems investigated. Bacteroids from root nodules of snake bean, however, were only capable of oxidizing C4-dicarboxylic acids and failed to oxidize any other carbon sources. Free-living cells of NGR234 possess inducible fructose and succinate uptake systems. These substrates are accumulated by active processes since accumulation is in hi bi ted by azide, 2,4-dini trop hen01 and carbonyl cyanide m-chlorophenyl hydrazone. Bacteroids failed to take up fructose although they actively accumulated succinate, suggesting that the latter substrate is significant in the development of an effective symbiosis.
Net aerobic H2 production and the induction of uptake hydrogenase activity in the nitrogenfixing Anabaena strains CA and 1F were strictly dependent upon the Ni2+ concentration in the growth medium. Ni2+ concentrations as low as 10 nM blocked H2 production and stimulated an uptake hydrogenase activity in whole cells. Two types of uptake hydrogenase activity were seen: a dark aerobic uptake approximately 30% as active as the H2 production rate, and a lightdependent activity in the presence of DCMU [3-(3,4-dichlorophenyl)-l, 1-dimethylurea] at low oxygen concentrations, amounting to about 50% of the H2 production rate. Together these activities may account for the strong control of net aerobic H2 production by nickel. A significant fraction of the Ni2+-stimulated uptake hydrogenase activity formed during the transition from nickel deficiency to nickel sufficiency was blocked by chloramphenicol. Nickel may be required for activation of an uptake hydrogenase, or for hydrogenase synthesis, or for synthesis of another protein which is involved in H2M uptake.
The effects of oxygen on growth and mannitol fermentation of eight strains of Streptococcus mutans were compared under aerobic and strictly anaerobic conditions. The growth of three strains was severely inhibited by oxygen, whereas the others were oxygen-tolerant. The growth of two of the oxygen-tolerant strains was significantly enhanced by oxygen. The activities of superoxide dismutase and NADH oxidase in extracts from aerobically grown bacteria showed a positive correlation with the growth rate under aerobic conditions. The activities of these enzymes in oxygen-sensitive strains grown aerobically were as small as those in anaerobically grown cultures. Moreover, the enzyme activities increased during aeration of anaerobically grown oxygen-tolerant strains, but not in oxygen-sensitive strains. In all strains, oxygen changed mannitol catabolism from heterolactic to homolactic fermentation. It was concluded that oxygen-tolerance of S. mutans is dependent on the ability of strains to induce NADH oxidase and superoxide dismutase.
A new obligate methanotroph was isolated and characterized. It was classified as a 'Methylosinus' species and named 'Methylosinus' sp. strain 6. Nitrogen metabolism in 'Methylosinus' 6 was found to be similar to other Type I1 methanotrophs, including the assimilation of nitrogen exclusively by the glutamine synthetaselglutamate synthase system. However, unlike other Type I1 methanotrophs, it appeared that glutamine synthetase activity was regulated by adenylylation in this organism. 'Methylosinus' 6 was grown in continuous culture with either dinitrogen or nitrate as sole nitrogen source under various dissolved oxygen tensions. Higher rates of methane oxidation and a more developed intracytoplasmic membrane system were found at lower oxygen tensions with nitrate as the nitrogen source but at higher oxygen tensions with dinitrogen as the nitrogen source, This suggested that carbon metabolism was influenced by nitrogen metabolism in this organism.