Biostimulation of indigenous microorganisms for bioremediation of oily hypersaline microcosms from the Arabian Gulf Kuwaiti coasts

•Hypersaline microcosms from Kuwait coast harbor hydrocarbonoclastic bacteria and archaea.•Those microorganisms could be biostimulated by the addition of cations and vitamins.•Such amendments were effective in oil-removal in the halostressed microcosms.•Cations are known to serve as osmoregulators in halophilic bacteria and archaea.•Results of this study pave the way for field bioremediation for halostressed sites.

Hypersaline soil and water samples were collected in summer and winter from the “sabkha” area at the Kuwaiti shore of the Arabian Gulf. Physicochemical parameters were analyzed, and found suitable for microbial oil-removal. Summer- and winter-microcosms were treated with individual cation (K+, Ca2+, Mg2+, Fe3+) salts, and with animal blood and commercial yeast, as cost-effective vitamin sources. Those microcosms were exposed to the open environment for six winter and six summer months, and analyzed for their hydrocarbonoclastic microorganisms at time zero and in two month intervals. The hydrocarbonoclastic microbial communities in the microcosms consisted of halophilic bacteria and haloarchaea. The constituent bacterial species varied according to the season. Three species, Dietzia kunjamensis, Marinobacter lacisalsi and Halomonas oxialensis consistently occurred both in summer- and winter-samples, but the remaining species were different. On the other hand, the haloarchaeal communities in summer and winter were quite similar, and consisted mainly of Haloferax spp and Halobacterium spp. Treating the microcosms with cations and with vitamin-containing natural products enhanced microbial numbers and oil-removal. The effectiveness of the cations in oil-removal was in the order; Fe3+ (94%) > Ca2+ (89%) > Mg2+ (85%) > K+ (82%). Thus, oily microcosms amended with trivalent and divalent cations lost most of the oil, and those amended with commercial yeast and with animal blood, as vitamin sources, lost 78% and 72% oil, respectively.

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