- Volume 134, Issue 1, 1988

Assimilation of fatty acids, fatty alcohols and sugars by Euglena gracilis Z was investigated with or without illumination. Propionate, butyrate, valeriate, hexanoate, myristate, palmitate, ethanol, propanol, lauryl alcohol, tridecanol and myristyl alcohol supported considerable growth. The assimilation of propionate, valeriate, palmitate, butanol, lauryl alcohol and myristyl alcohol were strictly light-dependent. The photoassimilation of myristyl alcohol was saturated by lower light intensity than photosynthesis and was not completely inhibited by a photosynthetic inhibitor, suggesting involvement of a photoreaction other than photosynthesis in the photoassimilation. d-Glucose, D-fructose, D-galactose, d-xylose, D-glyceraldehyde and glycerol also supported growth. Disaccharides were not used as the carbon source for growth. The difference in the mechanism of photoassimilation between myristyl alcohol and D-galactose is discussed.

Euglena gracilis pellicle, separated by sucrose density gradient centrifugation, had a high cobalamin (Cb1) binding activity. Of the Cb1 binding protein 65% was solubilized from E. gracilis pellicle by using 0·1% SDS/2 m-urea and the residual 35% by using 1% (w/v) SDS. Both of the Cb1 binding protein fractions showed a broad pH dependence for the binding of Cb1. No evidence for the involvement of SH-groups or metal ions in Cb1 binding was obtained. The K s values for cyanocobalamin of the proteins solubilized with 0·1% SDS/2 m-urea and with 1% SDS were 0·22 and 0·19 nm, respectively. The M r of a Cb1 binding polypeptide of each protein was estimated to be 38000 by SDS-PAGE. The Cb1 binding protein solubilized with 0·1% SDS/2 m-urea was purified to homogeneity. Inhibition experiments on Cb1 uptake in E. gracilis cells, using an antibody against the Cb1 binding protein solubilized with 0·1% SDS/2 m-urea, showed that the Cb1 binding proteins solubilized with 0·1% SDS/2 m-urea and 1% SDS take part in the slower secondary phase and in the initial rapid phase of Cb1 uptake in E. gracilis, respectively.

Cells of Pelobacter acidigallici strain WoGal grown in a continuous-flow microchamber with 0.1 mm-gallic acid as sole carbon source attached to the surface either irreversibly (nonmotile cells) or reversibly (motile cells). At low gallic acid concentrations (<0.1 mm) growth gave rise to microcolonies of < 128 cells which maintained their size by release of motile swarmer cells. Continuous biofilms were formed only at higher substrate concentrations (> 5 mm), at which both growth and cell deposition at the surface took place. Under starvation conditions, motile cells ceased to grow and were washed out, whereas irreversibly attached cells continued to divide but their daughter cells did not grow. The results suggest that this bacterium when growing at an attachment surface undergoes a complex life cycle including attachment and detachment processes and formation of motile swarmer cells.

Thirteen strains of Thermus isolated from New Zealand hot pools were screened for their ability to grow on minimal or near-minimal media and to exhibit extracellular protease activity. Environmental regulation of protease production by one such strain, Thermus Ok6, was investigated in detail. Protease activity was maximally derepressed during growth under conditions which lead to energy starvation (i.e. highly oxidized carbon substrate, oxygen limitation, slow growth rate and a high external pH), and was variably repressed by different nitrogen sources. These results suggest that the function of the enzyme is to scavenge carbon/energy and nitrogen. The protease was loosely attached to the cell under these growth conditions but could be released by growing the organism in high concentrations of trypticase peptone plus yeast extract, by exposing the culture to moderate shear forces or by washing cells in high ionic strength solutions of various inorganic salts, organic acids or amino acids. A simple and rapid procedure for the partial purification of the enzyme is described.

Biochemical, microbiological and genetic studies were done to characterize the mechanism of bacterial formation of N-nitrosomorpholine (NMOR) from morpholine and nitrite at neutral pH. In Escherichia coli and Proteus morganii, the nitrosating activity was markedly induced when bacteria were cultured under anaerobiosis in minimal medium containing nitrate, while in the presence of nitrite there was no induction. However, induction of the nitrosating activity in Pseudomonas aeruginosa occurred in anaerobic cultures in the presence of either nitrate or nitrite. The nitrosation capacity was also examined in various E. coli K12 mutants whose structural gene of either nitrate reductase or nitrite reductase was deleted. Nitrosation was not linked to the three (NADH-, formate-and glucose-dependent) nitrite reductases but was directly dependent on the presence of a nitrate reductase.

Some factors influencing the growth and production of extracellular lipase by Rhizopus oligosporus were studied. Highest yields of enzyme were obtained when Tweens were the carbon source. Soybean meal extract supported good growth and enzyme production. Carbohydrates, vegetable oils, proteins or amino acids did not stimulate lipase production. The fungus grew well with carbohydrate-or protein-supplemented media but not with oils, unless emulsified with a non-metabolizable gum. The production of biomass in static cultures was maximum at 35–40 °C after 4 d at pH 5·5. The yield of lipase was maximum at 25 °C after 3 d at pH 6·5. Shaking cultures enhanced growth but decreased lipase production.

The electrophoretic behaviour of freshly harvested spores of Aspergillus niger, Phanerochaete chrysosporium and Geotrichum candidum was determined in solution at various pH values. Freshly harvested spores of all three species lacked positive mobility at low pH values, suggesting a preponderance of acidic surface groups. Spores of the ‘non-aggregating’ fungus, G. candidum, had a pH-mobility curve (peak of negative mobility between pH 3 and 4) which was quite different to those of spores of the ‘aggregating’ fungi, A. niger and P. chrysosporium. The pH-mobility curve of swollen spores of A. niger which had been incubated in medium differed from that of freshly harvested spores, suggesting that changes in the wall that occur during germination alter the electrophoretic properties of the spores; swollen spores of A. niger, unlike freshly harvested spores, had a negative mobility maximum at pH 5·0.

After treatment with Junlon-110 (a polyacrylic acid), spores of all three species had similar pH-mobility curves and all had peaks of negative mobility at pH 4·0. The electrophoretic mobility of spores of P. chrysosporium at pH 6·5 increased linearly with the concentration (0·01–0·4%, w/v) of Junlon used in the pre-treatment; electrophoretic mobility after pre-treatment with 0·005-0·1% (w/v) Hostacerin (sodium polyacrylate) increased only up to 0·01% (w/v) Hostacerin. The results obtained show that Junlon-110 and Hostacerin bind to fungal walls, and it is possible that spore and hyphal aggregation is reduced by these compounds because of repulsion between particles resulting from ionized carboxyl groups on the polymer.

The biochemical basis for the antimicrobial effect of the carrot phytoalexin 6-methoxymellein (6-MM) was examined. At fungistatic concentrations 6-MM retarded the ability of Candida albicans to incorporate radioactive thymidine, uridine and leucine into biopolymers. When C. albicans was incubated with 6-MM, 260-nm-absorbing materials and 3H-labelled compounds leaked from the cells. The inhibitory effects of 6-MM on cell growth and membrane functions were, however, reduced as the concentration of divalent metal cations added to the medium was increased. 6-MM interacted with multilamellar liposomes constituted from phosphatidylcholine, cholesterol and dicetyl phosphate, or from phosphatidylcholine only, resulting in the release of glucose trapped in these liposomes. These results suggest that 6-MM exerts its toxic effects on susceptible cells as a result of its interaction with their membranes and disturbance of membrane-associated functions.