Isolation and characterization of a 9-fluorenone-degrading bacterial strain and its role in synergistic degradation of fluorene by a consortium

Pseudomonas mendocina MC2, able to use 9-fluorenone but not fluorene as its sole source of carbon and energy, was isolated. Identification of metabolites in growth media and washed cell suspensions indicated that strain MC2 metabolizes 9-fluorenone via angular dioxygenation of the ketone, to give 1,1a-dihydroxy-1-hydro-9-fluorenone, followed by the opening of the five-membered ring and further degradation of the resulting biphenyl derivative by reactions akin to those of biphenyl metabolism, which produce phthalate as an intermediate. The aim of this research was to study the biodegradation of fluorene by a co-culture of strain MC2 and Arthrobacter sp, strain F101, which grows on fluorene and simultaneously transforms a fraction of the substrate to 9-fluorenone, which accumulates as a dead-end product. Growing with 0.1 g fluorene/L, Arthrobacter sp. strain F101 caused the total removal of this compound from the cultures, but when this strain was grown with 1 g fluorene/L, only 16% of the fluorene was used. The addition of 9-fluorenone to cultures growing on fluorene showed that 9-fluorenone inhibits fluorene degradation. Finally, when Pseudomonas mendocina MC2 and Arthrobacter sp, strain F101 were co-cultured with 1 g fluorene/L as a sole source of carbon and energy, the growth of the strains completely removed fluorene in 2 days. 9-Fluorenone did not accumulate and the carbon assimilation into cell biomass was estimated as approximately 46%.