- Volume 128, Issue 7, 1982

The activity of ornithine decarboxylase (EC 4.1.1.17) and the intracellular pools of putrescine and spermidine were determined during zoospore germination and hormoneinduced sexual morphogenesis in Achlya ambisexualis. The specific activity of ornithine decarboxylase increased approximately 6-fold during zoospore germination and outgrowth in an enriched medium. Ornithine decarboxylase activity exhibited a rapid and transient 5·2-fold increase during hormone-induced differentiation of mycelium cultured in enriched media. In contrast, the enzyme activity did not increase following hormone treatment of mycelium cultured in a minimal medium, yet mycelial differentiation occurred normally. Fluctuations in intracellular concentrations of putrescine and spermidine, in general, correlated with changes in ornithine decarboxylase activity during hormone-induced differentiation and zoospore germination.

The biomass and residual limiting substrate profiles of chemostat grown Trichoderma aureoviride were typical of carbon-and of nitrogen-limited micro-organisms. Maintenance energy requirements partly accounted for the discrepancy between observed and predicted values of biomass concentration at low dilution rates under glucose limitation. At such low dilution rates the fungal mycelium became differentiated and sporulation occurred. The steady state glucose concentrations in glucose-limited cultures were higher than those predicted by chemostat theory; much closer agreement between observed and predicted values was achieved when a corrected max term ( Pitt & Bull, 1982a ) was used to calculate the residual glucose concentration. The measured growth parameters (μ max, μ man, K s, Y and m) for T. aureoviride had values similar to those reported for other species of filamentous fungi. The biomass concentration of fed-batch cultures increased linearly with time but glucose supplied at a rate three times higher than the maintenance requirement was insufficient to prevent sporulation. Mycelial RNA and protein concentrations increased with increasing dilution rate and were 30 and 40% lower under nitrogen limitation than under carbon limitation. DNA concentration was not influenced by dilution rate. The molar ratio of RNA: Mg2+ : K+ was 8:1:8 and was dilution rate independent. Only two polyamines, spermine and spermidine, were detected in T. aureoviride; they increased in concentration and proportion of the biomass as the dilution rate was raised but there was no evidence of their functional interchange ability with Mg2+ ions as reported for other fungi.

Activation of Phycomyces blakesleeanus spores resulted in the production of large amounts of pyruvate and 2-oxoglutarate. Incubation of dormant spores in 0·1 m-pyruvate at pH 3 resulted in a high internal pyruvate concentration but no 2-oxoglutarate was formed and neither germination nor respiration was stimulated. The capacity of isolated mitochondria to decarboxylate [1-14C]pyruvate was doubled by heat activation of the spores. This difference in activity disappeared when the mitochondria were subjected to treatments attacking the integrity of the mitochondrial membrane (detergent, resuspension in buffer without osmotic stabilizer). The increase in pyruvate decarboxylating activity was found only after heating the spores at temperatures also triggering germination of the spores. Pyruvate uptake by the mitochondria seems, therefore, to be a limiting factor in dormant spore metabolism.

The toxic effect of Lotus pedunculatus root flavolan towards fast-growing Lotus Rhizobium strains NZP2037 and NZP2213 was found to depend on the growth phase of the Rhizobium cells. Exponential-phase (24 h) cells of NZP2037 were more resistant to the flavolan and were able to bind three times more flavolan than exponential phase cells of NZP2213. Stationary-phase (72 h) cells of both strains were equally sensitive to the flavolan. The initial Rhizobium flavolan interaction was bacteriostatic; this lasted for 4 to 5 h for stationary-phase cells of both strains and for exponential-phase cells of NZP2213, but for approximately 10 h for exponential-phase cells of NZP2037. During this period flavolan bound to the surface of the cells causing aggregation of outer cell membrane components. Subsequently the cells became irregularly shaped and non-viable. Rhizobium sensitivity to flavolan was not related to extracellular polysaccharide production or composition. Polyethylene glycol overcame the inhibitory effects of flavolan towards exponential-phase NZP2213 cells if added before or at the same time as the flavolan.

Cyanobacteria respond to a decrease in light intensity by reversing their direction of gliding. The sensitivity of the phototactic response in Phormidium uncinatum increased two- to threefold under anaerobic conditions. Light-dependent changes in the membrane potential (∆ψ), as measured by tetraphenylphosphonium distribution, were also found to be larger in anaerobic conditions, suggesting that the photophobic response is governed by sensing of the protonmotive force (). The uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP), when added to P. uncinatum trichomes, also evoked a phobic response in a spatial gradient assay. The extent of repulsion by different concentrations of CCCP correlated with its ability to decrease ∆ψ. A viscous environment, exudates of an old culture, or high concentrations of Ca2+ (plus the ionophore A23187) caused oscillatory reversals and a partial asynchronization of cells within a trichome. EGTA or CCCP in high concentrations restored synchronization. Ethionine inhibited reversals and the addition of 10−6 m-Ca2+ (plus A23187) restored photophobic sensitivity. A depolarizing electrical potential spread from the leading end (the ‘head’) of the trichomes following a decrease in light intensity. It is suggested that sensing of or chemoeffectors leads to a methylation-requiring step followed by a taxic signal in the form of simultaneous changes in ∆ψ and Ca2+ concentration.

Candida utilis NRRL Y11868 was grown at several dilution rates in a glucose-limited chemostat. Protein and total carbohydrate contents of the cells varied markedly with dilution rate, primarily because significant glycogen synthesis occurred at the higher growth rates.