meliloti[22, 23] were found that might be involved in the uptake

of trehalose, sucrose, and/or maltose. These were encoded in plasmid p42f (ThuEFGK), and the chromosome (AglEFGK). Regarding trehalose degradation, neither E. coli treA- or treF- like genes for periplasmic or cytoplasmic trehalases, respectively, nor genes belonging to glycoside hydrolase family 15 trehalases [16, 17], were found in the R. etli genome. However, orthologs to the thuAB genes, which encode the major pathway for trehalose catabolism MLN2238 supplier in S. meliloti[21], were found in the chromosome and plasmid p42f. In addition, three copies of treC, encoding putative trehalose-6-phosphate hydrolases, were identified in the chromosome. All three TreC proteins belonged to the family 13 of glycoside hydrolases [16], but they did not cluster together (see the phylogenetic tree in Additional file 2: Figure S1B). The metabolism of trehalose in R. etli inferred from its genome sequence is summarized

in Figure 2. Figure 2 Scheme of trehalose metabolism in R. etli based on the annotated genome. Abbreviations used: Glu, D-glucose; Glu6P, D-glucose-6-phosphate; Glu1P, D-glucose-1-phosphate; Glutm, D-Glutamate, D-Glucsm6P, D-Glucosamine-6-phosphate; Fru, D-fructose; Fru6P, D-fructose-6-phosphate; Malt, Maltose; Mnt, mannitol, MOTS, Maltoolygosyltrehalose; Tre, Trehalose; TreP, Trehalose-6-phosphate; AlgEFGAK and ThuEFGK, putative Trehalose/maltose/sucrose ABC transporters; GlmS, glucosamine-6-phosphate synthase; Mtlk, Mannitol 2-dehydrogenase; Frk, Fructokinase, OtsA, Trehalose-6-phosphate synthase, OtsB,

Trehalose-6-phosphate phosphatase; Pgi, Smoothened antagonist Phosphoglucose isomerase; XylA, Xylose isomerase; TreC, Trehalose-6-phosphate hydrolase; TreS, Trehalose synthase; TreY, Maltooligosyl trehalose synthase; TreZ, Maltooligosyl trehalose trehalohydrolase, SmoEFGK, DAPT purchase Sorbitol/mannitol ABC transporter. Phylogenetic analysis of the two R. etli trehalose-6-phosphate synthases As two copies of OtsA (OtsAch and OtsAa, Figure 3A) were encoded by the R. etli genome, we investigated their Thiamine-diphosphate kinase phylogenetic relationship. First we aligned the amino acid sequences of both R. etli OtsA proteins with the sequences of characterized trehalose-6-P- synthases, and compared motifs involved in enzyme activity. All residues corresponding to the active site determined in the best studied E. coli trehalose-6-P synthase [54] were conserved in R. etli OtsAch and OtsAa (data not shown). However, the identity between both proteins was only of 48%, and the gene otsAa was flanked by putative insertion sequences in the R. etli genome. In addition, the otsAch copy and R. etli genome had a similar codon use, whereas the otsAa copy showed a different preference for Stop codon, and codons for amino acids as Ala, Arg, Gln, Ile,Leu, Phe, Ser, Thr, and Val. These findings suggested that otsAa might have been acquired by horizontal transfer.