Sinorhizobium fredii HH103 is a rhizobial strain showing a broad host-range of nodulation. In addition to the induction of bacterial nodulation genes, transition from a free-living to a symbiotic state requires complex genetic expression changes with the participation of global regulators. We have analyzed the role of the zinc-finger transcriptional regulator MucR1 from S. fredii HH103 under both free-living conditions and symbiosis with two HH103 host plants, Glycine max and Lotus burttii. Inactivation of HH103 mucR1 led to a severe decrease in exopolysaccharide (EPS) biosynthesis but enhanced production of external cyclic glucans (CG). This mutant also showed increased cell aggregation capacity, as well as a drastic reduction in nitrogen-fixation capacity with G. max and L. burttii. However, in these two legumes, the number of nodules induced by the mucR1 mutant was significantly increased and decreased respectively with respect to the wild-type strain, indicating that MucR1 can differently affect nodul...

Using different Sinorhizobium meliloti strains as hosts, we isolated eight new virulent phages from the rhizosphere of the coastal legume Medicago marina. Half of the isolated phages showed a very narrow host range while the other half exhibited a wider host range within the strains tested. Electron microscopy studies showed that phages M_ort18, M_sf1.2, and M_sf3.33 belonged to the Myoviridae family with feature long, contractile tails and icosaedral head. Phages I_sf3.21 and I_sf3.10T appeared to have filamentous shape and produced turbid plaques, which is a characteristic of phages from the Inoviridae family. Phage P_ort11 is a member of the Podoviridae, with an icosahedral head and a short tail and was selected for further characterization and genome sequencing. P_ort11 contained linear, double-stranded DNA with a length of 75239 bp and 103 putative open reading frames. BLASTP analysis revealed strong similarities to Escherichia phage N4 and other N4-like phages. This is the first report of filamentous and N4-like phages that infect S. meliloti.

A Gram-stain-negative, aerobic, motile, rod-shaped bacterium, strain SC13E-S71^T, was isolated from tuff, volcanic rock, where the Roman catacombs of Saint Callixtus in Rome, Italy, was excavated. Analysis of 16S rRNA gene sequences revealed that strain SC13E-S71^Tbelongs to the genus Sphingopyxis , and that it shows the greatest sequence similarity with Sphingopyxis chilensis DSM 14889^T(98.72 %), Sphingopyxis taejonensis DSM 15583^T(98.65 %), Sphingopyxis ginsengisoli LMG 23390^T(98.16 %), Sphingopyxis panaciterrae KCTC 12580^T(98.09 %), Sphingopyxis alaskensis DSM 13593^T(98.09 %), Sphingopyxis witflariensis DSM 14551^T(98.09 %), Sphingopyxis bauzanensis DSM 22271^T(98.02 %), Sphingopyxis granuli KCTC 12209^T(97.73 %), Sphingopyxis macrogoltabida KACC 10927^T(97.49 %), Sphingopyxis ummariensis DSM 24316^T(97.37 %) and Sphingopyxis panaciterrulae KCTC 22112^T(97.09 %). The predominant fatty acids were C_18 : 1ω7c, summed feature 3 (iso-C_15 : 02-OH and/or C_16 : 1ω7c), C_14 : 02-OH and C_16 : 0. The predominant menaquinone was MK-10. The major polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylcholine and sphingoglycolipid. These chemotaxonomic data are common to members of the genus Sphingopyxis . However, a polyphasic approach using physiological tests, DNA base ratios, DNA–DNA hybridization and 16S rRNA gene sequence comparisons showed that the isolate SC13E-S71^Tbelongs to a novel species within the genus Sphingopyxis , for which the name Sphingopyxis italicasp. nov. is proposed. The type strain is SC13E-S71^T( = DSM 25229^T = CECT 8016^T).