A bacterial strain isolated from crude oil-contaminated sediments displays chemotaxis towards hydrocarbons

LANFRANCONI MP, MURIALDO SE, GONZÁLEZ N AND STUDDERT CA

Buenos Aires

Congreso; XVII Congreso Latinoamericano y X Congreso Argentino de Microbiología (AAM); 2004

Asociación Argentina de Microbiología

Flagellated bacteria are able to migrate in response to gradients of certain chemicals by a process called chemotaxis. Hydrophobic pollutants, like alkanes, are often distributed in non-aqueous phases, and their low solubility limits bioavailability. Thus, any process that decreases the average distance between degrader organisms and pollutants should accelerate degradation. One such process may be bacterial chemotaxis. In order to investigate whether hydrocarbon-degrading microorganisms respond chemotactically to hydrocarbons and different carbon sources,we isolated a strain, that we called MagB, from coastal sediments contaminated with crude oil (Magdalena, Pcia. De Buenos Aires, Argentina). A sediment sample obtained from the contaminated site was enriched in hydrocarbon degraders using mineral medium supplemented with hexadecane  as the only source of carbon and energy. After the enrichment, we obtained a bacterial strain with the ability to degrade hexadecane. Cells of strain MagB were Gram negative rods, aerobic, oxidase positive, catalase negative and highly motile. When streaked onto LB agar or MS plus hexadecane agar plates and incubated for five days, they developed tiny (0.2-0.5 mm), transparent colonies. In liquid cultures, they occurred as single cells, but tended to form cell aggregates. The bacterium was characterized by sequencing of its 16S rRNA gene (500 bp). The resulting sequence showed 97% of similarity with Aquabacterium parvum. MagB degrades gas oil, hexadecane, pentadecane, Casaminoacids, and several organic acids but neither sugars nor pyruvate, glycerol and propionic acid. The strain was tested for chemotaxis towards its specific substrates: -         In soft agar plates, MagB responded chemotactically to all the non-hydrocarbon carbon sources tested (as long as they supported growth) and also to gas oil and hexadecane. -         Chemotaxis to hexadecane was confirmed using the agarose-in-plug qualitative assay These results indicate that a bacterial strain, indigenous from the site where the oil spill occurred,  responds chemotactically towards the same hydrocarbons that serve as carbon source for growth. Such a response might be relevant to the efficiency of this strain as biodegrader. Further experimental work is necessary in order to establish whether the chemotactic response is inducible by growth with hexadecane or other alkanes and if the alkane metabolism is required for the chemotaxis response.