Physiological characterization of Mycobacterium sp. strain 1B isolated from a bacterial culture able to degrade high-molecular-weight polycyclic aromatic hydrocarbons

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Abstract
The aim of this study was to further characterize a bacterial culture (VUN 10,010) capable of benzo[a]pyrene cometabolism. The bacterial culture, previously characterized as a pure culture of Stenotrophomonas maltophilia (VUN 10,010), was found to also contain another bacterial species (Mycobacterium sp. strain 1B), capable of degrading a similar range of PAH substrates. Analysis of its 16S rRNA gene sequence and growth characteristics revealed the strain to be a fast-growing Mycobacterium sp., closely related to other previously isolated PAH and xenobiotic-degrading mycobacterial strains. Comparison of the PAH-degrading characteristics of Mycobacterium sp. strain 1B with those of S. maltophilia indicated some similarities (ability to degrade phenanthrene and pyrene), but some differences were also noted (S. maltophilia able to degrade fluorene, but not fluoranthene, whereas Mycobacterium sp. strain 1B can degrade fluoranthene, but not fluorene). Unlike the S. maltophilia culture, there was no evidence of benzo[a]pyrene degradation by Mycobacterium sp. strain 1B, even in the presence of other PAHs (ie pyrene) as co-metabolic substrates. Growth of Mycobacterium sp. strain 1B on other organic carbon sources was also limited compared with the S. maltophilia culture. This study isolated a Mycobacterium strain from a bacterial culture capable of benzo[a]pyrene cometabolism. The Mycobacterium strain displays different PAH-degrading characteristics to those described previously for the PAH-degrading bacterial culture. It is unclear what role the two bacterial strains play in benzo[a]pyrene cometabolism, as the Mycobacterium strain does not appear to have endogenous benzo[a]pyrene degrading ability. This study describes the isolation and characterization of a novel PAH-degrading Mycobacterium strain from a PAH-degrading culture. Further studies utilizing this strain alone, and in combination with other members of the consortium, will provide insight into the diverse roles different bacteria may play in PAH degradation in mixed cultures and in the environment.

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