Homologs from sulfur oxidation (Sox) and methanol dehydrogenation (Xox) enzyme systems collaborate to give rise to a novel pathway of chemolithotrophic tetrathionate oxidation.
Mol Microbiol
; 109(2): 169-191, 2018 Jul.
Article
in En
| MEDLINE
| ID: mdl-29669166
ABSTRACT
The SoxXAYZB(CD)2 -mediated pathway of bacterial sulfur-chemolithotrophy explains the oxidation of thiosulfate, sulfide, sulfur and sulfite but not tetrathionate. Advenella kashmirensis, which oxidizes tetrathionate to sulfate, besides forming it as an intermediate during thiosulfate oxidation, possesses a soxCDYZAXOB operon. Knock-out mutations proved that only SoxBCD is involved in A. kashmirensis tetrathionate oxidation, whereas thiosulfate-to-tetrathionate conversion is Sox independent. Expression of two glutathione metabolism-related proteins increased under chemolithotrophic conditions, as compared to the chemoorganotrophic one. Substrate-dependent oxygen consumption pattern of whole cells, and sulfur-oxidizing enzyme activities of cell-free extracts, measured in the presence/absence of thiol inhibitors/glutathione, corroborated glutathione involvement in tetrathionate oxidation. Furthermore, proteome analyses detected a sulfiteacceptor oxidoreductase (SorAB) exclusively under chemolithotrophic conditions, while expression of a methanol dehydrogenase (XoxF) homolog, subsequently named thiol dehydrotransferase (ThdT), was found to increase 3- and 10-fold during thiosulfate-to-tetrathionate conversion and tetrathionate oxidation respectively. A thdT knock-out mutant did not oxidize tetrathionate but converted half of the supplied 40 mM S-thiosulfate to tetrathionate. Knock-out of another thiosulfate dehydrogenase (tsdA) gene proved that both ThdT and TsdA individually converted â¼ 20 mM S-thiosulfate to tetrathionate. The overexpressed and isolated ThdT protein exhibited PQQ-dependent thiosulfate dehydrogenation, whereas its PQQ-independent thiol transfer activity involving tetrathionate and glutathione potentially produced a glutathionesulfodisulfane adduct and sulfite. SoxBCD and SorAB were hypothesized to oxidize the aforesaid adduct and sulfite respectively.
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Language:
En
Journal:
Mol Microbiol
Journal subject:
BIOLOGIA MOLECULAR
/
MICROBIOLOGIA
Year:
2018
Document type:
Article
Affiliation country:
India