in accumulating osmoprotectant solutes. A) Schematic representation of the repertory of genes putatively related to accumulation of classical solutes under hyperosmotic stress in representatives of each α-proteobacterial family. The intensity of the blue color reflects the identity relative to the corresponding gene of E. coli in local sequence alignment; a white box means that the organism does not possess a homolog for the corresponding gene. Sme, Bja, Ccr, Pzu, Rsp, Rde, Sphm, Zmo, Rru, Apt, Rri, Wol and Eco correspond to Sinorhizobium meliloti 1021, Bradyrhizobium japonicum USDA110, Caulobacter crescentus CB15, Phenylobacterium zucineum, Rhodobacter sphaeroides 2.4.1, Roseobacter denitrificans, Sphingomonas sp. MM-1, Zymomonas mobilis subsp. mobilis ZM4, Rhodospirillum rubrum ATCC11170, Acetobacter pasteurianus IFO 3283–01, Rickettsia rickettsii Sheila Smith, Wolbachia sp.wMel and Escherichia coli. K-12 MG1655, respectively. Accession numbers (locus number) of the corresponding homologs are shown in Additional file 1: Table S1. B) Relative abundance of transcript (circle) and protein (triangle) corresponding to genes presumably involved in accumulation of classical solute following either sucrose (blue) or salt stress (orange). Significant changes are denoted as open symbols. Values are log2 and represent the average of three independent biological experiments. Absence of data for a gene indicates that no homologue was identified in C. crescentus genome (white color in panel A). Particularly for protein data, the absence can also indicate that the corresponding spot was not determined by mass spectrometry analysis, so the relative intensity could not be measured.