title: Analysis of the xplAB-containing gene cluster involved in the bacterial degradation of the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine.
abstract: Repeated use of the explosive compound hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) on military land has resulted in significant soil and groundwater pollution. Rates of degradation of RDX in the environment are low, and accumulated RDX, which the U.S. Environmental Protection Agency has determined is a possible human carcinogen, is now threatening drinking water supplies. RDX-degrading microorganisms have been isolated from RDX-contaminated land; however, despite the presence of these species in contaminated soils, RDX pollution persists. To further understand this problem, we studied RDX-degrading species belonging to four different genera (Rhodococcus, Microbacterium, Gordonia, and Williamsia) isolated from geographically distinct locations and established that the xplA and xplB (xplAB) genes, which encode a cytochrome P450 and a flavodoxin redox partner, respectively, are nearly identical in all these species. Together, the xplAB system catalyzes the reductive denitration of RDX and subsequent ring cleavage under aerobic and anaerobic conditions. In addition to xplAB, the Rhodococcus species studied here share a 14-kb region flanking xplAB; thus, it appears likely that the RDX-metabolizing ability was transferred as a genomic island within a transposable element. The conservation and transfer of xplAB-flanking genes suggest a role in RDX metabolism. We therefore independently knocked out genes within this cluster in the RDX-degrading species Rhodococcus rhodochrous 11Y. Analysis of the resulting mutants revealed that XplA is essential for RDX degradation and that XplB is not the sole contributor of reducing equivalents to XplA. While XplA expression is induced under nitrogen-limiting conditions and further enhanced by the presence of RDX, MarR is not regulated by RDX.
authors.affiliation: Centre for Novel Agricultural Products, Department of Biology, University of York, York, United Kingdom Department of Biotechnology and Medical Engineering, Faculty of Biosciences and Medical Engineering, Universiti Teknologi Malaysia, Skudai, Johor, Malaysia.
authors.forename: Chun Shiong
authors.initials: CS
authors.lastname: Chong
authors.affiliation: Centre for Novel Agricultural Products, Department of Biology, University of York, York, United Kingdom.
authors.forename: Dana Khdr
authors.initials: DK
authors.lastname: Sabir
authors.affiliation: Centre for Novel Agricultural Products, Department of Biology, University of York, York, United Kingdom.
authors.forename: Astrid
authors.initials: A
authors.lastname: Lorenz
authors.affiliation: Centre for Novel Agricultural Products, Department of Biology, University of York, York, United Kingdom.
authors.forename: Cyril
authors.initials: C
authors.lastname: Bontemps
authors.affiliation: Department of Civil and Environmental Engineering, University of Washington, Seattle, Washington, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Andeer
authors.affiliation: Department of Civil and Environmental Engineering, University of Washington, Seattle, Washington, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Stahl
authors.affiliation: Department of Civil and Environmental Engineering, University of Washington, Seattle, Washington, USA.
authors.forename: Stuart E
authors.initials: SE
authors.lastname: Strand
authors.affiliation: Centre for Novel Agricultural Products, Department of Biology, University of York, York, United Kingdom.
authors.forename: Elizabeth L
authors.initials: EL
authors.lastname: Rylott
authors.affiliation: Centre for Novel Agricultural Products, Department of Biology, University of York, York, United Kingdom neil.bruce@york.ac.uk.
authors.forename: Neil C
authors.initials: NC
authors.lastname: Bruce
mesh_terms: D039903:Actinobacteria / Q000235:genetics* / Q000378:metabolism*; D001711:Biotransformation; D053834:Explosive Agents / Q000378:metabolism*; D055786:Gene Knockout Techniques; D008969:Molecular Sequence Data; D005810:Multigene Family; D010084:Oxidation-Reduction; D017422:Sequence Analysis, DNA; D014227:Triazines / Q000378:metabolism*
chemical_list: D053834:Explosive Agents; D014227:Triazines; C009160:cyclonite