Thermal Inactivation of a Deep-Sea Barophilic Bacterium, Isolate CNPT-3

Abstract

The barophilic deep-sea bacterium, isolate CNPT-3, was inactivated by exposures to temperatures between 10 and 32�C at atmospheric pressure. Inactivation in samples from warmed cell suspensions was measured as the loss of colonyforming ability (CFA) at 10�C and 587 bars. At atmospheric pressure, there was a slow loss of CFA even at 10�C. The loss of CFA was rapid above 20�C and only slightly affected by high pressures. The first-order rate constants for thermal inactivation fit the Arrhenius equation with an activation energy of 43 kcal (ca. 179.9 kJ)/mol. Light microscopy and scanning transmission electron microscopy revealed morphological changes due to warming of the cells. The changes ensued the loss of CFA. The results supported the hypothesis from an earlier work that indigenous (autochthonous) deep-sea bacteria from cold deep seas are both barophilic and psychrophilic. If ultimately sustained, these characteristics may be useful in designing experiments to assess the relative importance of the autochthonous and allochthonous bacteria in the deep sea. The data were used to evaluate how barophilic bacteria may have been missed in many investigations because of warming of the cells during sample retrieval from the sea or during cultivation in the laboratory. The evaluation revealed the need for temperature and pressure data during retrieval of samples and cultivation in the laboratory. Most deep-ocean microbiology may be possible with thermally insulated equipment for retrieval from the sea and with high-pressure vessels for laboratory incubations.