Oxygen uptake rates in the hyperthermophilic anaerobe Thermotoga maritima grown in a bioreactor under controlled oxygen exposure: clues to its defence strategy against oxidative stress

A 2.3-L bioreactor was specially adapted to grow hyperthermophilic microorganisms under controlled conditions of temperature, pH, redox potential and dissolved O-2. Using this bioreactor regulated at 80A degrees C and pH 7.0, we demonstrated that Thermotoga maritima recovered its growth despite being exposed to oxygen for a short time (30 min with a maximum concentration of 23 mu M of dissolved oxygen). Under these conditions, we demonstrated that O-2 uptake rate, estimated at 73.6 mu moles O-2 min(-1) g proteins(-1) for dissolved oxygen, was optimal and constant, when dissolved oxygen was present in a range of 22-5 mu M. Transcription analyses revealed that during short oxygen exposure, T. maritima expressed genes coding for enzymes to deal with O-2 and reactive oxygen species (ROS) such as peroxides. Thus, genes encoding ROS-scavenging systems, alkyl hydroperoxide reductase (ahp), thioredoxin-dependent thiol peroxidase (bcp 2) and to a lesser extent neelaredoxin (nlr) and rubrerythrin (rbr), were found to be upregulated during oxygen exposure. The oxygen reductase FprA, homologous to the rubredoxin-oxygen oxidoreductase (ROO) found in Desulfovibrio species, is proposed as a primary consumer of O-2 in T. maritima. Moreover, the expression of frpA was shown to depend on the redox (Eh) level of the culture medium.