Regulation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) metabolism in Shewanella halifaxensis HAW-EB4 by terminal electron acceptor and involvement of c-type cytochrome

Abstract

Regulation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) metabolism in Shewanella halifaxensis HAW-EB4 by terminal electron acceptor and involvement of c-type cytochrome Shewanella halifaxensis HAW-EB4 was previously isolated for its potential to mineralize hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) from a UXO (unexploded ordnance)-contaminated marine sediment site near Halifax Harbor. The present study was undertaken to determine the effect of terminal electron acceptors (TEA) on the growth of strain HAW-EB4 and on the enzymic processes involved in RDX metabolism. The results showed that aerobic conditions were optimal for bacterial growth, but that anaerobic conditions in the presence of trimethylamine N-oxide (TMAO) or in the absence of TEA favoured RDX metabolism. RDX as a substrate neither stimulated respiratory growth nor induced its own biotransformation. Strain HAW-EB4 used periplasmic proteins to transform RDX to both nitroso [hexahydro-1-nitroso-3,5-dinitro-1,3, 5-triazine (MNX), hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX), and hexahydro-1,3, 5-trinitroso-1,3,5-triazine (TNX)] and ring cleavage products (such as methylenedinitramine), with more nitroso formation in cells grown on TMAO or pre-incubated in the absence of TEA. Using spectroscopy, SDS-PAGE and haem-staining analysis, strain HAW-EB4 was found to produce different sets of c-type cytochromes when grown on various TEA, with several more cytochromes produced in cells grown on TMAO. Crude cytochromes from total periplasmic proteins of TMAO-grown cells metabolized RDX to products similar to those found in assays using total periplasmic proteins and whole cells. To prove the involvement of cytochrome in RDX metabolism, we monitored dithionite-or NADH-reduced cytochromes by their absorbance at the a (551 nm) or c (418-420 nm) bands during anaerobic incubation with RDX. In both cases we found that RDX biotransformation was accompanied by oxidation of reduced cytochrome. Furthermore, O 2 , an oxidant of reduced cytochrome, inhibited RDX transformation. The present results demonstrate that S. halifaxensis HAW-EB4 metabolizes RDX optimally under TMAO-reducing conditions, and that c-type cytochromes are involved.

The periplasmic nitrate reductase in Shewanella: the resolution, distribution and functional implications of two NAP isoforms, NapEDABC and NapDAGHB

“…Shewanella halifaxensis HAW-EB4 produces nitrous oxide but not N 2 during anaerobic growth on nitrate-augmented media (Zhao et al, 2006(Zhao et al, , 2008. The lack of N 2 production from N 2 O by S. halifaxensis HAW-EB4 is consistent with the absence of nosZ in the genome.…”

“…The genome of Shewanella denitrificans OS217, which from experiment has been established as a vigorous denitrifier (Brettar et al, 2002), contains only the nap-a operon. The genomes of S. oneidensis MR-1, which has been established as a respiratory nitrate ammonifier (Cruz-Garcia et al, 2007;Myers & Myers, 1997;Schwalb et al, 2002), and S. halifaxensis HAW-EB4 (Zhao et al, 2006(Zhao et al, , 2008 contain only the nap-b operon.…”

Biodegradation of RDX and MNX with Rhodococcus sp. Strain DN22: New Insights into the Degradation Pathway

“…NH 2 CHO was first derivatized by treatment with pentafluorobenzylhydroxylamine (24) and analyzed by LC-MS as its deprotonated molecular mass ion [M-H] -. NDAB and MEDINA were determined by HPLC and by comparison with authentic materials (15). NH 4 + was determined colorimetrically using EPA method 350.1 (25).…”

Steroid degradation in Comamonas testosteroni

“…383 (accession: NC_007511) [76], Cu. taiwanensis LMG 19424 (accession: NC_010530) [77], Shewanella pealeana ATCC700345 (accession: NC_009901), S. halifaxensis HAW-EB4 (accession: NC_010334) [78,79]. ), and Pseudoalteromonas haloplanktis TAC125 (accession: NC_007481) [80,81]), whose deduced amino acid sequence of putative steroid degradation genes correspond to tesB to ORF33 are showing higher homology than others (Figure 12.).…”