Ability of the So-Called Obligate Hydrocarbonoclastic Bacteria to Utilize Nonhydrocarbon Substrates Thus Enhancing Their Activities Despite their Misleading Name.

BACKGROUND: The group of the so-called obligate hydrocarbonoclastic bacteria (OHCB) are marine microorganisms affiliated with the genera Alcanivorax, Cycloclasticus, Oleiphilus and Thalassolituus. This small group plays a major role in oil-bioremediation in marine ecosystems. Marinobacter and Planomicrobium are considered related to this group. The OHCB are claimed to be obligate to hydrocarbon nutrition. This study argues against this claim. RESULTS: Four Alcanivorax species, three Marinobacter species and Planomicrobium okeanokoites from the Arabian/Persian Gulf proved to be not obligate to hydrocarbon nutrition. Although the eight strains grew on crude oil, n-octadecane and phenanthrene as sole carbon substrates, their growth was weaker than on certain nonhydrocarbon, organic compounds viz. peptone, glutamic acid, pyruvic acid, sucrose, mannose and others. Glucose and lactose failed to support the growth of seven of the eight tested strains. Mannose was utilized by five and sucrose by six strains. The well-known intermediate metabolite; pyruvic acid was utilized by all the eight strains, and lactic acid by five strains. In batch cultures, all the tested species consumed higher proportions of peptone than of n-alkanes and phenanthrene. When peptone and crude oil were provided together into the medium, the OHCB started to consume peptone first, and the enriched bacterial populations consumed oil effectively. Added nonhydrocarbon substrates biostimulated oil-consumption by all OHCB species. CONCLUSION: The tested OHCB species are not obligate hydrocarbon-utilizers. This provides them with the merit of survival, should their marine ecosystems become oil- or hydrocarbon-free. The fact that conventional, organic substrates biostimulated hydrocarbon-consumption by the tested bacterial species confirms the facultative nature of those organisms and is interesting from the practical point of view.

Lipid and fatty acid profile of Geobacillus kaustophilus in response to abiotic stress.

Geobacillus kaustophilus is an important food-borne, spore-forming, thermotolerant bacterium. It has a good potential for biotransformation of steroid hormones, such as progesterone and testosterone. In this study, we report G. kaustophilus membrane lipid modifications in response to temperature shock, salinity, incubation time, and pH. Total lipids significantly increased in response to increasing temperature, incubation time, and salt concentration. However, the bacterium presented a significant decrease in the accumulation of total lipids in response to pH shock. The ratio of branched-chain fatty acids/straight-chain fatty acids decreased significantly under all stress conditions. With an increase in temperature, incubation time, and salt concentration, the ratio of iso-fatty acids/anteiso-fatty acids increased significantly, while this ratio remained unaffected by changes in the pH of the growth medium. Our results suggest a modification occurs in the bacterial membrane structure in response to temperature, salinity, incubation time, and pH shock. The variable abiotic stress resulted in a multiple increase in odd-numbered-carbon and low-melting-point anteiso-branched-chain fatty acids, helping the membrane keep its integrity, fluidity, and function for growth of the bacteria under abiotic stress conditions.