e. seed-coated) inoculants [1, 2]. Therefore, besides symbiotic efficiency, improvement of survival of rhizobia under conditions of the above abiotic constraints may constitute a competitive trait for either native or inoculant rhizobia, to persist in soil and solid inoculant

formulations, TGF-beta Smad signaling and to improve the colonization and/or infection process. The responses to osmotic, drought and heat stress in bacteria involve very complex adaptation mechanisms, but one common element of the three responses is the synthesis of protectant molecules named compatible solutes [3]. Indeed, the role of compatible solutes goes beyond osmotic adjustment alone to protection of cells and cell components from freezing, desiccation, high temperature, and oxygen radicals, as well as to serve as sources of carbon, energy and nitrogen [4]. Trehalose (O-α,-D-glucosyl-[1→1]-α-D-glucoside) has been found as the main compatible solute in almost any rhizobial strain check details tested so far, and its accumulation has been detected in free-living cells, bacteroids, and nodules [2, 5–8]. Trehalose accumulation by R. leguminosarum

bv trifolii and Sinorhizobium meliloti reaches its maximal levels at stationary phase of growth [5, 7, 9]. Out of the five different routes known for trehalose biosynthesis, three pathways have been found in rhizobia. First, the OtsA-OtsB route, which is very well conserved among insects, plants, fungi and bacteria, this website involves the transfer of glucose from UDP-glucose DNA ligase to glucose-phosphate to form trehalose-6-phosphate by trehalose-6-phosphate synthase (OtsA). Then, a trehalose-6-phosphate phosphatase (OtsB) dephosphorylates this intermediate to produce trehalose [2, 5, 7, 10]. Second, trehalose synthase (TreS), first described in mycobacteria [11],

catalyzes the reversible conversion of maltose and trehalose. In the case of Bradyrhizobium japonicum, trehalose is accumulated to a greater extent in a treS mutant, suggesting that TreS is involved in trehalose degradation to maltose [2]. A third pathway first discovered in Rhizobium sp. M-11 [12] and the archaeon Sulfolobus acidocaldarius[13], converts the terminal unit of a linear maltodextrin (e.g., glycogen or starch) to trehalose via maltooligosyl trehalose synthase, encoded by treY, and maltooligosyl trehalose trehalohydrolase (TreZ). Apart from stress protectant, trehalose also serves as a carbon and energy source for many bacteria, including rhizobia. In soil, trehalose originates from nodules during nodule senescence [14] and as an excretion product from fungi [15]. There are several known pathways for trehalose catabolism in microorganisms. The major enzyme involved in the turnover of trehalose, trehalase (α,α,1,1-glucosyl hydrolase), usually belongs to families 37 and 15 of glycoside hydrolases [16, 17].