Degradation of long-chain alkanes through biofilm formation by bacteria isolated from oil-polluted soil

Three bacteria, Novosphingobium sp. S1, Gordonia amicalis S2 and Gordonia terrae S5, were isolated from a crude oil polluted soil and investigated for their ability to utilize long-chain alkanes (C16-C30). The strains were able to use n-hexadecane, n-octadecane and paraffins as carbon and energy source, although at different extents. Growth with alkanes, resulted in the formation of a biofilm at the alkane-water interface. Growth was shown to occur only if cells had access to the alkane-water interface suggesting that biofilm formation was required to assimilate these hydrophobic substrates. The interfacial access to alkanes is also supported by the ability of the strains to adhere to n-hexadecane, with Gordonia amicalis S2 and Gordonia terrae S5 exhibiting a much stronger adhesion than Novosphingobium sp. S1. None of the strains released biosurfactant into the culture medium which is consistent with an interfacial access to alkanes. LC-MS analyses revealed the release into the extracellular medium of 8-hydroxyhexadecanedioic acid by Novosphingobium sp. S1 and Gordonia amicalis S2, and 8-hydroxyhexadecanoic acid and 7-hydroxyhexadecanoic by Gordonia terrae S5. The production of these hydroxylated carboxylic acids substantiates the degradation of n-hexadecane by the strains although their physiological significance remains to be elucidated.