Insights into trehalose synthase function in the rhizobium Paraburkholderia phymatum STM815T under abiotic stresses and during symbiosis

The beta-proteobacterium Paraburkholderia phymatum STM815T is a diazotrophic rhizobium that is highly competitive for legume root nodulation and is resistant to abiotic stresses, including heat, low pH, or drought stress. A gene coding for a potential trehalose synthase and localized on the symbiotic plasmid (SptreS) was among the most highly up-regulated genes in microoxic conditions and in symbiosis. In this study, we observed that cells grown in microaerobic conditions produced 5.8 times more trehalose than in aerobic conditions. Accordingly, a P. phymatum SptreS mutant accumulated 29.5% less trehalose than the wild-type strain in microaerobic conditions. During symbiosis with common bean, the SptreS mutant showed a 58.8% lower nitrogenase activity compared to the wild-type strain. Furthermore, in absence of SptreS P. phymatum was more sensitive to H2O2-induced oxidative stress and to freezing conditions and formed filaments. These results expand our knowledge on the behavior of this beta-rhizobium under microoxic conditions and on the role of the enzyme trehalose synthase in rhizobial resistance to abiotic stresses and in symbiotic efficiency.