Utilization of toluene and xylenes by a nitrate-reducing strain of Pseudomonas maltophilia under low oxygen and anoxic conditions

Abstract

A nitrate‐reducing strain of Pseudomonas maltophilia isolated from sewage sludge degrades toluene, and at least two isomers of mixed xylenes, either in the presence of 2% oxygen or under anoxic conditions when nitrate is present. When individual isomers of xylene are provided only meta and para‐xylene are utilized. When mixed xylenes are provided all three isomers may be utilized. In cultures limited by electron acceptor availability, succinate, when present as the major carbon source, does not prevent hydrocarbon utilization. Toluene and xylenes continued to be utilized either with limiting nitrate alone, or with limiting nitrate and oxygen present simultaneously when a hundred‐fold excess of succinate is present in the medium. The data suggest that in groundwater containing low levels of oxygen and nitrate, or nitrate only as the electron acceptor, aromatic hydrocarbons may continue to be utilized even in the presence of an excess of readily‐degradable non‐hydrocarbon organic substrates. These data have implications for bioremediation studies. The strain of Pseudomonas maltophilia used in this study does not degrade benzene, and the presence of benzene does not affect toluene utilization.

Biostimulation strategies : For in situ biodegradation of complex aromatic contaminant mixtures in groundwater

“…Thus, sequential electron acceptor usage can potentially contribute to the removal of aromatic organic compounds such as benzene where the most challenging step for microorganisms is the breakdown of the stabile ring structure (Firmino et al, 2018;Weelink et al, 2010). Furthermore, oxygen based conversion generally yields more microbial biomass and can thereby enhance denitrification processes beneficial for the biodegradation of subsurface contaminants (Su & Kafkewitz, 1994). There are several publications focusing on the microaerobic biodegradation of individual BTEX compounds (Aburto et al, 2009;Su & Kafkewitz, 1994;Yerushalmi et al, 2001Yerushalmi et al, , 2002 and on BTEX as a mixture (Da Silva et al, 2005;Firmino et al, 2018;S.-R. Hutchins et al, 1992;Olsen et al, 1995;Siqueira et al, 2018) with diverting outcomes on biodegradability of the individual compounds of the BTEX and other aromatic compounds.…”

“…Furthermore, oxygen based conversion generally yields more microbial biomass and can thereby enhance denitrification processes beneficial for the biodegradation of subsurface contaminants (Su & Kafkewitz, 1994). There are several publications focusing on the microaerobic biodegradation of individual BTEX compounds (Aburto et al, 2009;Su & Kafkewitz, 1994;Yerushalmi et al, 2001Yerushalmi et al, , 2002 and on BTEX as a mixture (Da Silva et al, 2005;Firmino et al, 2018;S.-R. Hutchins et al, 1992;Olsen et al, 1995;Siqueira et al, 2018) with diverting outcomes on biodegradability of the individual compounds of the BTEX and other aromatic compounds. Studies with much more complex mixtures of organic aromatic compounds are scarce, while mixtures -and not the individual compounds-are generally found in contaminated sites (Deeb et al, 2001;Gusmão et al, 2006;Zhou et al, 2011).…”

“…In literature, microaerobic conditions were defined as below 2 mg O2 L -1 (Olsen et al, 1995) however, a range of oxygen concentrations were also reported for the aerobic conversion of the BTEX compounds under microaerobic conditions. Su and Kafkewitz (1994) tested BTX degradation at 2% oxygen, and reported that xylenes and toluene could be degraded, but benzene was recalcitrant. Yerushalmi et al (2001) tested benzene biodegradation under different DO concentrations (1 to 0.05 mg O2 L -1 ) and showed that at lower DO concentrations, the removal efficiency of benzene decreased (100% to 34%).…”