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

SOLAR VENERO, E.C.; TRIBELLI, P.M.; LÓPEZ, N.I.

Congreso; X congreso Argentino de Microbiología General (SAMIGE); 2014

Cold environments constitute stressing habitats that limit bacterial survival and colonization of new ecological niches due to the effect of unfavorable conditions. Exposure to cold 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 ofgrowing at low temperatures with high stress resistance in association with the accumulation of large amounts of polyhydroxybutyrate (PHB). Screening of a mini Tn5 library allowed the detection/identification of 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 proteins involved in its biosynthesis are encoded in the pqqABCDE cluster. The pqqB mutant strain was unable to grow and survive when exposed to low temperatures and freezing conditions, but presented a high growth rate at 28°C in comparison with the wild type strain. In addition, a significant increase in oxygen consumption was observed in the pqqB strain. The expression of pqqB gene in the wild type strain did not show significant differences between 28°C and 10°C. PQQ has been also proposed as a reactive oxygen species (ROS) scavenger. As an increase of ROS has been reported at cold conditions, experiments were conducted in order to assess if the cold sensitive phenotype of the pqqB strain was related to oxidative stress. 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 in 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. Our results demonstrate that pqqB gene is essential for growth and survival under low temperatures, and that this phenotype does not seem to be associated with an increase of oxidative stress. However, the molecular mechanism involved in this novel pqq phenotype associated with cold sensitivity remains to be elucidated.