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

Abstract

The beta-proteobacterium Paraburkholderia phymatum STM815^T 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 (_Sp treS) was among the most highly upregulated 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 _Sp treS mutant accumulated 29.5% less trehalose than the wild-type strain in microaerobic conditions. During symbiosis with common bean, the _Sp treS mutant showed a 58.8% lower nitrogenase activity compared to the wild-type strain. Furthermore, in absence of _Sp treS 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.