Abstract
Due to their remarkable resistance to extreme conditions, Deinococcaceae strains are of great interest to biotechnological prospects. However, the physiology of the extremophile strain Deinococcus geothermalis has scarcely been studied and is not well understood. The physiological behaviour was then studied in well-controlled conditions in flask and bioreactor cultures. The growth of D. geothermalis type strains was compared. Among the strains tested, the strain from the German Collection of Microorganisms (Deutsche Sammlung von Mikroorganismen DSM) DSM-11302 was found to give the highest biomass concentration and growth rate: in a complex medium with glucose, the growth rate reached 0.75 h−1 at 45 °C. Yeast extract concentration in the medium had significant constitutive and catalytic effects. Furthermore, the results showed that the physiological descriptors were not affected by the inoculum preparation steps. A batch culture of D. geothermalis DSM-11302 on defined medium was carried out: cells grew exponentially with a maximal growth rate of 0.28 h−1 and D. geothermalis DSM-11302 biomass reached 1.4 g·L−1 in 20 h. Then, 1.4 gDryCellWeight of biomass (X) was obtained from 5.6 g glucose (Glc) consumed as carbon source, corresponding to a yield of 0.3 CmolX·CmolGlc−1; cell specific oxygen uptake and carbon dioxide production rates reached 216 and 226 mmol.CmolX−1·h−1, respectively, and the respiratory quotient (QR) value varied from 1.1 to 1.7. This is the first time that kinetic parameters and yields are reported for D. geothermalis DSM-11302 grown on a mineral medium in well-controlled batch culture.
Highlights
Bacteria belonging to the Deinococcaceae family possess very interesting properties as they are well-known for being the most radiation-resistant bacteria
The results showed that the Thermus 162 (TH162) medium and the Holland medium were not adapted for the growth of these strains of D. geothermalis
The variability of physiological behaviour between these strains could be related to the geographical locations where they have been isolated; differences of biochemical properties have already been described by Ferreira et al, in carbon source assimilation studies [2]
Summary
Bacteria belonging to the Deinococcaceae family possess very interesting properties as they are well-known for being the most radiation-resistant bacteria. Deinococcus species can survive and repair their genome even after an exposition to high radiation levels [1,2] or other environmental stress agents including ultraviolet light, oxidative stress and desiccation [3,4,5]. Their ability to tolerate high temperatures, a broad range of pH and chemicals compounds make Deinococcaceae good candidates for production of bioenergy products such as bioethanol and metabolites derivatives [6]. Many genetic engineering studies have been conducted in order to understand Deinococcus radiodurans’ efficient system for repairing DNA, and to develop strategies for bioremediation using radiation resistant microorganisms [7,8,9]
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