Comparison of n-eicosane and phenanthrene removal by pure and mixed cultures of two marine bacteria

The biotransformation activities of two hydrocarbonoclastic marine bacteria, Corynebacterium sp. and Sphingomonas sp. 2MPII, on n-eicosane and phenanthrene were investigated. During a 56-day experiment, in pure and mixed cultures, Corynebacterium sp. and Sphingomonas sp. 2MPII removed about 70% of the initial n-eicosane and phenanthrene concentrations (1 and 0.4 g L−1, respectively). In pure cultures, culturable cell abundances increased over time, from 0.8 to 8.6×10−11 CFU L−1 (Corynebacterium sp.) and from 2.1 to 16×10−11 CFU L−1 (Sphingomonas sp. 2MPII ) but remained barely constant in mixed cultures. We defined a biotransformation index based on the number of culturable cells rather than the culture protein content, with the biotransformation cell yield (BCY) expressed in grams hydrocarbon CFU−1 per day to better characterize hydrocarbon removal in pure and mixed cultures. The BCY was markedly higher in mixed than in pure cultures, increasing by a factor of 2–10.7 and 2.3–4.7 for n-eicosane and phenanthrene removal, respectively.