Quantification of Chemotaxis-Related Alkane Accumulation in Acinetobacter baylyi Using Raman Microspectroscopy

Alkanes are one of the most widespread contaminants in the natural environment, primarily as a consequence of biological synthesis and oil spills. Many indigenous microbes metabolize alkanes, and the chemotaxis and accumulation in some strains has been identified. For the first time, we apply Raman microspectroscopy to identify such chemotaxis-related affinity, and quantify the alkane concentrations via spectral alterations. Raman spectral alterations were only found for the alkane chemo-attractant bacteria Acinetobacter baylyi ADP1, not for Pseudomonas fluorescence, which exhibits limited chemotaxis toward alkane. The significant alterations were attributed to the strong chemotactic ability of A. baylyi enhancing the affinity and accumulation of alkane molecules on cell membranes or cellular internalization. Spectral fingerprints of A. baylyi significantly altered after 1-h exposure to pure alkanes (dodecane or tetradecane) and alkane mixtures (mineral oil or crude oil), but not monocyclic aromatic hydrocarbons (MAHs) or polycyclic aromatic hydrocarbons (PAHs). A semilog linear regression relationship between Raman spectral alterations and alkane concentrations showed its feasibility in quantifying alkane concentration in environmental samples. Pure alkanes or alkane mixtures exhibited different limits of detection and regression slopes, indicating that the chemotaxis-related alkane accumulation in A. baylyi is dependent on the carbon chain length. This work provides a novel biospectroscopy approach to characterize the chemotaxis-related alkane bioaccumulation, and has immense potential for fast and high-throughput screening bacterial chemotaxis.