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. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12866-019-1406-x) contains supplementary material, which is available to authorized users.