Submersed culture production of extracellular wax esters by the marine bacterium Fundibacter jadensis.

Fundibacter jadensis strain T9, a marine gram-negative bacterium, was isolated from the intertidal sediment of the German North Sea coast by our group. The cells were able to produce considerable amounts of extracellular wax esters when cultivated with n-alkanes (hexadecane or tetradecane) as a carbon source. The dependence of wax ester production and the composition of the purified wax on different culture conditions (C:N:P ratio and dissolved oxygen tension) were tested. Our results show that wax ester production was not directly growth-linked. The C:N:P ratio had no significant influence on the yield of alkane-free purified wax. The dissolved oxygen tension affected the produced amount of the alkane-free purified wax and the composition of the purified wax; when lower than 2% it decreased the yield of purified wax and led to an altered wax ester composition. Tetradecane as a carbon source enhanced the spectrum of the wax ester composition.

Hexadecane mineralization in oxygen-controlled sediment-seawater cultivations with autochthonous microorganisms.

Laboratory studies investigated the influence of dissolved oxygen tension (DOT) on microbial degradation of hexadecane in cultures with sediment-seawater suspensions. With a fermentor system, it was possible to adjust and regulate different oxic conditions (DOTs between 0.4 and 80% of oxygen saturation) as well as anoxia. The effects of DOT reduction on the amount and rate of hexadecane degraded and on the degree of mineralization and on the production of biomass were investigated. When the DOT was reduced from 80% to 5%, no dependence of the investigated parameters on the oxygen concentration was found. The amount of hexadecane degraded was constant, with an average value of 86% of the initially applied amount. The degradation rate was constant even down to 1% DOT, with an average value of 0.15 mg of hexadecane per g of sediment per h (16.2 mg liter-1 h-1). The mean degree of mineralization was 70% of the initially applied hexadecane, and biomass production reached a value of about 1.5 g per g of hexadecane consumed. A significant influence on the degradation process was detected only with DOTs below 1%. The degree of mineralization and the amount of degraded hexadecane decreased, whereas the degradation rate was still unaffected. Under anoxic conditions, no hexadecane degradation occurred within 190 h. The fact that the hexadecane biodegradation rate was constant down to at least 0.04% DOT shows that the actual oxygen concentration is of minor importance as long as the oxygen supply is high enough to guarantee the oxygen-dependent degradation step.

Use of batch and fed-batch fermentation for studies on the variation of glutathione content and its influence on the genotoxicity of methyl-nitro-nitrosoguanidine in yeast.

We have applied fermenter techniques to analyse the variations of glutathione (GSH) content in cultures of the diploid strain D7 of Saccharomyces cerevisiae. Choosing various experimental conditions of controlled batch and fed-batch fermentation we give evidence that the GSH levels of the yeast cultures depend on growth phase, the carbon source supply and the carbon source metabolism in an unexpectedly complex manner. Additionally, we analysed yeast cells with low GSH levels which were obtained either by depleting GSH with chloroacetophenone (CN) chemically or by using a GSH-deficient diploid strain (gsh1/gsh1). In order to study the relevance of the factors influencing the GSH concentration for genotoxicity testing in yeast we have used N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) which is activated by GSH. We show that in cells which are GSH proficient the extent of genotoxicity of MNNG correlates well with the GSH levels in the cells. Conditions of high GSH content (stationary phase of growth) corresponds with high genotoxic activity of MNNG, whereas conditions of low GSH content as logarithmic growth, glucose repression, GSH deficiency caused by the gsh1 mutation and GSH depletion by CN treatment correspond with a very moderate genotoxic effect of MNNG. These findings emphasize the necessity to use metabolically highly standardized cells for genotoxicity testing, since the carbon source catabolism, the concentration of glucose, growth rate and possibly other parameters influence the metabolization of xenobiotic agents in yeast.