Adaptation of the Hydrocarbonoclastic Bacterium Alcanivorax borkumensis SK2 to Alkanes and Toxic Organic Compounds: a Physiological and Transcriptomic Approach

Abstract

The marine hydrocarbonoclastic bacterium Alcanivorax borkumensis is able to degrade mixtures of n -alkanes as they occur in marine oil spills. However, investigations of growth behavior and physiology of these bacteria when cultivated with n -alkanes of different chain lengths (C 6 to C 30 ) as the substrates are still lacking. Growth rates increased with increasing alkane chain length up to a maximum between C 12 and C 19 , with no evident difference between even- and odd-numbered chain lengths, before decreasing with chain lengths greater than C 19 . Surface hydrophobicity of alkane-grown cells, assessed by determination of the water contact angles, showed a similar pattern, with maximum values associated with growth rates on alkanes with chain lengths between C 11 and C 19 and significantly lower values for cells grown on pyruvate. A. borkumensis was found to incorporate and modify the fatty acid intermediates generated by the corresponding n -alkane degradation pathway. Cells grown on distinct n -alkanes proved that A. borkumensis is able to not only incorporate but also modify fatty acid intermediates derived from the alkane degradation pathway. Comparing cells grown on pyruvate with those cultivated on hexadecane in terms of their tolerance toward two groups of toxic organic compounds, chlorophenols and alkanols, representing intensely studied organic compounds, revealed similar tolerances toward chlorophenols, whereas the toxicities of different n -alkanols were significantly reduced when hexadecane was used as a carbon source. As one adaptive mechanism of A. borkumensis to these toxic organic solvents, the activity of cis-trans isomerization of unsaturated fatty acids was proven. These findings could be verified by a detailed transcriptomic comparison between cultures grown on hexadecane and pyruvate and including solvent stress caused by the addition of 1-octanol as the most toxic intermediate of n -alkane degradation.