Response of the thermophile Thermus sp RQ-1 to hyperbaric air in batch andfed-batch cultivation

The effects of increased air pressure in a culture of the thermophilic micr oorganism Thermus sp. RQ-1 were investigated. Cell growth dependence on oxy gen supply was investigated in a fermenter at atmospheric pressure. Total o xygen depletion from the medium for low values of k(L)a was observed during the exponential growth phase. It was possible with this strain to enhance the oxygen transfer rate by increasing the air pressure. Cell productivity was improved by pressurisation up to 0.56 MPa for batch cultivation; and an induction of the antioxidant enzymes, superoxide dismutase and catalase, w as observed with the rise in pressure. Cell pre-cultivation under pressuris ed conditions conferred to the cells more resistance to an exposure to hydr ogen peroxide and more sensitivity to paraquat (methyl viologen). The usefu lness of bioreactor pressurisation on the cultivation of Thermus sp. RQ-1 w as demonstrated for fed-batch operation, with the attainment of higher cell densities. A two-fold increase in cell mass productivity was obtained by t he use of hyperbaric air (0.5 MPa). With the pressurisation of the head-spa ce in the reactor, it was also possible to eliminate the loss of liquid by evaporation, which amounted to more than 10% at 70 degrees C and atmospheri c pressure.