- Volume 126, Issue 1, 1981

Sporulation of Aspergillus niger and Aspergillus ochraceus was induced in a continuous tower fermenter by restricting growth by nutrient limitation. Shock carbon limitation produced no sporulation, but the gradual decrease of sucrose or starch supply to A. niger produced slight sporulation. Gradual nitrate limitation produced no sporulation, while a shock decrease in nitrate concentration caused heavy sporulation of both organisms. The previously unobserved morphology of the sporulating structures produced was much simplified under nitrate limitation, but similar to sub-aerial morphology under carbon limitation. Maintenance energy values for sucrose and starch were calculated for A. niger and for starch for A. ochraceus. The continuous tower fermenter system was found to be ideal for controlling organism morphology and thus sporulation.

Carboxymethylcellulose was used as a model substrate in batch and continuous cultures in a study of cellulose metabolism and the synthesis of β-glucosidase and endoglucanase by Trichoderma koningii. The maximum growth rate on CM-cellulose compared favourably with that on cellulose. In batch cultures mycelial inoculum was more effective than spore inoculum in initiating synthesis of both enzymes. Synthesis of β-glucosidase in larger amounts than the maximum provided by growth from the initial mycelial inoculum was achieved by encouraging renewed growth by replenishing half the spent medium when the carbohydrate had been consumed: the same treatment failed to enhance the yield of endoglucanase. Growth from a spore inoculum gave considerably lower yields of β-glucosidase but ultimately doubled that of the endoglucanase. The delayed synthesis of endoglucanase was also overcome and its yield increased up to fourfold by restricted aeration, whereas that of β-glucosidase was unaffected. Maximum synthesis of both enzymes was obtained simultaneously in continuous culture together with improved yields. The nature of the hydrolysis of cellulose and the effect of its products, cellobiose and glucose, are considered in relation to the synthesis of β-glucosidase and the endoglucanase.

High concentrations of sodium succinate (100 mm) were inhibitory to the growth of Rhizobium leguminosarum. Spontaneous succinate-resistant mutants could be isolated at low frequency. One class of mutants (sucI) appeared to metabolize succinate at an enhanced rate. The other class (sucII) showed decreased rates of succinate uptake and metabolism. These sucII mutants failed to show nitrogenase activity within pea root nodules.

Free-living cells of Rhizobium leguminosarum 3841 have inducible oxidation systems for the catabolism of histidine, malonate, p-hydroxybenzoate, glycerol, mannitol and sorbitol. In addition to p-hydroxybenzoate, strain 3841 is able to use a variety of other aromatic substrates as sole carbon source. Cultured free-living bacteria of this strain have constitutive systems for the catabolism of acetate, pyruvate, succinate, fumarate, malate, glucose, fructose, sucrose, lactose, ribose and arabinose. However, isolated pea bacteroids of the same strain are unable to oxidize monosaccharides or disaccharides although they can oxidize the organic acids succinate, fumarate, malate and pyruvate.

Desulfovibrio vulgaris (Hildenborough), D. desulfuricans (Essex 6) and D. gigas (holotype) are shown to grow on H2 and sulphate as sole energy source. Lithotrophic growth on H2 and sulphate is thus not a unique property of a few newly isolated Desulfovibrio strains as previously reported ( Badziong et al., 1978 ).