- Volume 138, Issue 8, 1992

The effect of different growth conditions on the glycogen and poly-β-hydroxybutyrate (PHB) content of the cyanobacterium Spirulina maxima is described. Under photoautotrophic growth conditions without any nutrient limitation, S. maxima exhibited a glycogen content of between 7.1 and 10.7% of cell dry wt, whereas PHB was undetectable. When S. maxima was grown under mixotrophic conditions in the presence of acetate, the intracellular PHB concentration increased to more than 3% of dry wt, while glycogen content remained within the range of 5 to 6% of cell dry wt. Nitrogen starvation favoured glycogen accumulation (up to 60 to 70% of dry wt), while the PHB content remained low (up to 0.7% of dry wt), even after prolonged nitrogen starvation. Inhibition of protein synthesis, induced by addition of azaserine, led to the accumulation of glycogen (up to 52% of cell dry wt) but did not stimulate PHB synthesis. Under phosphorus-limited growth conditions, glycogen and PHB accumulated (up to 23% and 1.2% of cell dry wt, respectively) only after the exhaustion of intracellular phosphorus reserves. Shifting the culture from low to high light irradiance induced a rapid accumulation of glycogen (up to 34% of cell dry wt after 9 h) but did not induce PHB synthesis. Results are discussed in terms of the metabolic significance of PHB synthesis in cyanobacteria, and suggest that this polymer acts exclusively as a disposal mechanism to eliminate excess reducing equivalents.

The aim of this investigation was to perform an extensive screening using HPLC and 13C-NMR spectroscopy to disclose the spectrum of osmolytes produced by aerobic heterotrophic and anoxygenic phototrophic eubacteria. The most predominant solutes detected within a wide range of marine and halophilic micro-organisms were two recently discovered tetrahydropyrimidines ectoine and hydroxyectoine, which were synthesized in response to osmotic stress.

Piromyces sp. strain E2, an anaerobic fungus isolated from an Indian elephant (hindgut fermenter) was tested for its ability to ferment a range of substrates. The fungus was able to use bagasse, cellobiose, cellulose, fructose, glucose, lactose, mannose, starch, wheat bran, wheat straw, xylan and xylose. Formate and acetate were the main fermentation products after growth on these substrates. The amount of carbon found in the fermentation products of cultures, in which substrate digestion was complete averaged 88.5 mM, or 59% of the carbon offered as substrate. No growth was observed on other substrates tested. Lactose, starch, cellobiose and filter paper cellulose were good inducers of cellulolytic and xylanolytic enzymes. Cellulolytic and xylanolytic enzymes were produced constitutively by Piromyces strain E2, although enzyme activities were generally lower after growth on glucose and other soluble sugars. Complex substrates (bagasse, wheat bran, and wheat straw) were good inducers for xylanolytic enzymes but not for cellulolytic enzymes. The extracellular protein banding pattern after SDS-PAGE was therefore only slightly affected by the growth substrate. Identical β-glucosidase and endoglucanase activity patterns were found after growth on different substrates. This indicated that differences in enzyme activities were not the result of secretion of different sets of isoenzymes although it remains possible that the relative amount of each isoenzym produced is influenced by the growth substrate.

Mutants resistant to 3-aminobenzamide, a known inhibitor of ADP-ribosyltransferase, were obtained from Streptomyces griseus IFO 13189, a streptomycin-producing strain. One (strain no. 4), which had significantly reduced ADP-ribosyltransferase activity, was analysed in detail. Mutant 4 displayed a conditional phenotype with respect to cultivation temperature. At 30 °C, it exhibited severely reduced ability to produce aerial mycelium (on solid medium) and submerged spores and streptomycin (in liquid culture), but this ability was fully restored at 25 °C. The mutant produced A-factor normally, regardless of cultivation temperature, and exhibited normal ability to accumulate ppGpp intracellularly. SDS-PAGE analyses of cellular proteins labelled by [32P]NAD revealed that an ADP-ribosylated protein with a molecular size of 44 kDa, which appeared in sporulating cultures of the parent strain, was missing from the mutant grown at the non-permissive temperature (30 °C). Genetic analysis showed that the aba mutation conferring resistance to 3-aminobenzamide was tightly linked to the altered phenotype. Failure to ADP-ribosylate certain cellular protein(s), presumably due to the aba mutation, may be responsible for impaired differentiation in this mutant.

The in vivo functioning of the alanine/D-alanyl-D-alanine pathway of Escherichia coli was investigated by determining prefnsor pool levels and specific enzyme activities under various growth conditions. Cells grown on D- or L-alanine showed several remarkable features compared with cells grown on other carbon sources: 10-fold higher values of the D-alanyl-D-alanine and the UDP-MurNAc-pentapeptide pools, a 240-fold increase of the alanine racemase activity, and the absence of bacteriolysis after treatment with D-cycloserine at high concentrations (50 μg ml−1). In cells grown on glucose, D-cycloserine (1 μg ml−1) led to depletion of the D-alanyl-D-alanine pool and to lysis, which was efficiently antagonized by chloramphenicol. A threefold increase of the dipeptide pool was observed when cells were treated with chloramphenicol alone. The alanine racemase activity was lowest in glucose-grown cells and the D-alanine: D-alanine ligase and D-alanyl-D-alanine-adding activities were the same whatever the carbon source. Molecular masses of 53–56 kDa and 56–60 kDa were estimated for the partially purified inducible alanine racemase and D-alanine: D-alanine ligase respectively.

Twenty-eight non-spreading mutants of the gliding bacterium Cytophaga johnsonae were generated by different approaches and subsequently studied to determine whether they possessed traits commonly assumed to be associated with such mutants. Many non-spreading variants of C. johnsonae purportedly possess a static cell surface as opposed to the dynamic one of the motile parent strain. A moving cell surface has been supposed to be responsible for an array of traits associated with motile cells, but missing in non-motile cells. Phage sensitivity, chitin digestion and the ability of cells to move latex beads over their surfaces are some of the alleged motility-dependent traits. Also, it has been reported that non-spreading mutants possess a cell surface that is less hydrophobic than that of the parent strain. We characterized our collection of mutants in relation to the above mentioned traits to determine whether these characteristics indeed required a moving cell surface. Our findings showed that neither phage sensitivity nor chitin digestion were motility-dependent. In addition we noted that non-spreading mutants could possess surfaces more (rather than less) hydrophobic than the motile parent strain.