PQQ BIOSYNTHESIS GENES ARE ESSENTIAL FOR GROWTH UNDER COLD CONDITIONS IN Pseudomonas extremaustralis

SOLAR VENERO ESMERALDA C.; TRIBELLI PAULA M.; OPPEZO OSCAR; LOPEZ NANCY I.

Mar del Plata

Congreso; X CONGRESO ARGENTINO DE MICROBIOLOGÍA GENERAL SAMIGE; 2014

SAMIGE

Cold environments constitute stressing habitats that limit bacterial survival and colonization of new ecological niches due to the effect of unfavorable conditions. Exposure to these conditions provokes changes in solubility, reaction kinetics, membrane fluidity, degradation, stability and conformation of proteins and gene expression so bacteria that live in such conditions must have some physiological adaptations. Pseudomonas extremaustralis is an Antarctic bacterium capable of growing at low temperatures with high stress resistance in association with the accumulation of large amounts of polyhidroxybutyrate (PHB). During the construction of a mini Tn5 library we detected a clone carrying a mutation in pqqB gene that was unable to grow under cold conditions. Pyrroloquinoline quinone (PQQ) is as cofactor of several enzymes and the enzymes involved in its biosynthesis are encoded in the pqqABCDE cluster. This pqqB mutant strain is unable to grow and survive when exposed to low temperatures and freezing conditions, but presents a high growth rate at 28C. The expression of pqqB gene for the wild type strain did not show significant differences between 28°C and 10°C. An increase of reactive oxygen species (ROS) has been reported at cold conditions and PQQ has been proposed as a ROS scavenger. Consequently, experiments in order to assess if the cold sensitive phenotype of the pqqB strain was related to oxidative stress were conducted. Sensitivity to H2O2 was measured by a disk inhibition assay for the wild type and the pqqB strain grown at 28C. The resistance to H2O2 was similar for both strains. Moreover, we tested growth at 10°C for both strains under microaerobic conditions and in the presence of antioxidant compounds. None of the tested conditions suppressed the cold sensitive phenotype, as the mutant was unable to grow in the presence of the antioxidant compounds or low oxygen tension at 10°C. In addition, Oxygen consumption was measured for both strains, showing a significant increase in the pqqB strain. Our results demonstrate that pqqB gene is essential for growth and survival under low temperatures, and that this phenotype is not associated with an increase of oxidative stress. However, the molecular mechanism of this novel phenotype remains to be elucidated.