Effect of Adaptation to Continuous Osmotic Stress on the Bacterium Rhodospirillum Rubrum

abstract

English

In recent years, there have been major advances in industry which, in addition to improving the quality of everyday life, has also caused massive enviromental pollution (e.g. plastic pollution). This issue could be solved by replacing the petrochemical plastics by in nature biodegrable materials such as polyhydroxyalkanoates (PHAs) also produced by purple non-sulfur bacterium Rhodospirillum rubrum. The advantage of this bacterium as a PHA producer is its metabolic versatility and thus its ability to survive in various conditions (light, dark, anaerobic or aerobic conditions, etc.) This work focused on the adaptation of R. rubrum to osmotic stress by evolutionary engineering with the goal of increased PHA production. First, the bacterial strain was exposed to different salt concentrations in order to optimize the appropriate salt concentration for subsequent adaptation experiment. During the evolutionary experiments, the PHA content of the adapted strains was analyzed by GC-FID, and the total dry biomass was also determined. After the evolutionary experiments, the cultures were exposed to selected stressors (high temperature; osmotic shock and freezing-thawing cycles) followed by viability analysis of by flow cytometry. In the last experiment, a comparison was made between the adapted and wild-type strains, where both strains were cultivated in media with different carbon sources (respectively acetate or fructose). The medias also contained different salt concentrations (0, 40 and 60 g/l NaCl). After culturing, the PHA content was determined by GC-FID. We were able to confirm the positive effect of continuous exposure to osmotic stress of 40 g/l NaCl on PHA production in R. rubrum with the concentration of 15–20 % throughout the experiment. The method of evolutionary engineering seems to be appropriate for increasing PHA production in R. rubrum. In the future, it would be worthwhile to extend this work by including adaptations to other stressors in combination with carbon substrates other than those used in this work.

adaptation, evolutionary engineering, Rhodospirillum rubrum, polyhydroxyalkanoates, osmotic stress

PACASOVÁ, V.; FIALA, T.; SLANINOVÁ, E.; OBRUČA, S.

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