An oxygen reduction chain in the hyperthermophilic anaerobe Thermotoga maritima highlights horizontal gene transfer between Thermococcales and Thermotogales

Abstract

The hyperthermophile Thermotoga maritima, although strictly anaerobic, is able to grow in the presence of low amounts of O(2). Here, we show that this bacterium consumes O(2) via a three-partner chain involving an NADH oxidoreductase (NRO), a rubredoxin (Rd) and a flavo-diiron protein (FprA) (locus tags: TM_0754, TM_0659 and TM_0755, respectively). In vitro experiments showed that the NADH-dependent O(2) consumption rate was 881.9 (± 106.7) mol O(2) consumed min(-1) per mol of FprA at 37°C and that water was the main end-product of the reaction. We propose that this O(2) reduction chain plays a central role in the O(2) tolerance of T. maritima. Phylogenetic analyses suggest that the genes coding for these three components were acquired by an ancestor of Thermotogales from an ancestor of Thermococcales via a single gene transfer. This event likely also involved two ROS scavenging enzymes (neelaredoxin and rubrerythrin) that are encoded by genes clustered with those coding for FprA, NRO and Rd in the ancestor of Thermococcales. Such genomic organization would have provided the ancestor of Thermotogales with a complete set of enzymes dedicated to O(2)-toxicity defence. Beside Thermotogales and Thermococcales, horizontal gene transfers have played a major role in disseminating these enzymes within the hyperthermophilic anaerobic prokaryotic communities, allowing them to cope with fluctuating oxidative conditions that exist in situ.

Histidine ligand variants of a flavo-diiron protein: effects on structure and activities

“…The room temperature O 2 R activity of Tm FDP is comparable to that reported for ROO [20], while the NOR activity is significantly lower [4]. These relative O 2 R vs NOR activities are consistent with the in vivo evidence of an O 2 scavenging function for Tm FDP [17, 25]. We have produced and characterized Tm FDP variants in which H90 was substituted with either Asn or Ala.…”

Active Site Metal Occupancy and Cyclic Di-GMP Phosphodiesterase Activity of Thermotoga maritima HD-GYP

“…24,25 T. maritima is classified as an anaerobe, although it can grow under an atmosphere containing low levels of O 2 . 26,27 Given this reducing growth environment and our results showing comparable c-di-GMP PDE activity with divalent iron and manganese, TM0186 could function with di- and trimetal active sites occupied by either divalent iron or manganese in vivo and could switch between dimetal and trimetal forms depending on intracellular metal availability. TM0186 contains an N-terminal REC regulatory domain, which has been suggested to regulate substrate accessibility to the active site in other HD-GYPs.…”

A Detoxifying Oxygen Reductase in the Anaerobic Protozoan Entamoeba histolytica

“…FDPs have been shown to be highly and constitutively expressed both in prokaryotes (in some cases incorporating an oxidative stress response operon [8,18]) and in protozoa (10,25,32). However, an increase in expression upon oxygen exposure has been observed for only one other FDP, that from the hyperthermophilic bacterium Thermotoga maritima, which shows an increase in protein levels with unmatched transcriptional levels and is proposed to sustain the growth of this "strict" anaerobe under microaerophilic conditions (20)(21)(22). The cytoplasmic abundance and increased protein levels in response to oxygen exposure suggest a potential similar function for EhFdp1 in E. histolytica.…”