The aim of the present study was to characterize the endophytic bacterial strain designated MSR1 that was isolated from inside the non-nodulating roots of Medicago sativa after surface-sterilization. MSR1 was identified as Enterobacter cloacae using both 16S rDNA gene sequence analysis and API20E biochemical identification system (Biomerieux, France). Furthermore, this bacterium was characterized using API50CH kit (Biomerieux, France) and tested for antibacterial activities against some food borne pathogens. The results showed that E. cloacae consumed certain carbohydrates such as glycerol, d-xylose, d-maltose and esculin melibiose as a sole carbon source and certain amino acids such as arginine, tryptophan ornithine as nitrogen source. Furthermore, MSR1 possessed multiple plant-growth promoting characteristics; phosphate solubility, production of phytohormones acetoin and bioactive compounds. Inoculation of Pisum sativum with MSR1 significantly improved the growth parameters (the length and dry weight) of this economically important grain legume compared to the non-treated plants. To our knowledge, this is the first report addressing E. cloacae which exist in roots of alfalfa growing in Al-Ahsaa region. The results confirmed that E. cloacae exhibited traits for plant growth promoting and could be developed as an eco-friendly biofertilizer for P. sativum and probably for other important plant species in future.

Summary: Biological oxidation of methane to methanol by aerobic bacteria is catalysed by two different enzymes, the cytoplasmic or soluble methane monooxygenase ( sMMO ) and the membrane‐bound or particulate methane monooxygenase ( pMMO ). Expression of MMOs is controlled by a ‘copper‐switch’, i.e. sMMO is only expressed at very low copper : biomass ratios, while pMMO expression increases as this ratio increases. Methanotrophs synthesize a chalkophore, methanobactin, for the binding and import of copper. Previous work suggested that methanobactin was formed from a polypeptide precursor. Here we report that deletion of the gene suspected to encode for this precursor, mbnA , in M ethylosinus trichosporium OB3 b, abolishes methanobactin production. Further, gene expression assays indicate that methanobactin, together with another polypeptide of previously unknown function, MmoD , play key roles in regulating expression of MMOs . Based on these data, we propose a general model explaining how expression of the MMO operons is regulated by copper, methanobactin and MmoD . The basis of the ‘copper‐switch’ is MmoD , and methanobactin amplifies the magnitude of the switch. Bioinformatic analysis of bacterial genomes indicates that the production of methanobactin‐like compounds is not confined to methanotrophs, suggesting that its use as a metal‐binding agent and/or role in gene regulation may be widespread in nature.

An aerobic, methane-oxidizing bacterium (strain RS11D-Pr^T) was isolated from rice rhizosphere. Cells of strain RS11D-Pr^Twere Gram-stain-negative, motile rods with a single polar flagellum and contained an intracytoplasmic membrane system typical of type I methanotrophs. The strain utilized methane and methanol as sole carbon and energy sources. It could grow at 20–37 °C (optimum 31–33 °C), at pH 6.8–7.4 (range 5.5–9.0) and with 0–0.2 % (w/v) NaCl (there was no growth at above 0.5 % NaCl).pmoAandmmoXgenes were present. The ribulose monophosphate and/or ribulose bisphosphate pathways were used for carbon assimilation. Results of sequence analysis of 16S rRNA genes showed that strain RS11D-Pr^Tis related closely to the generaMethylococcus,Methylocaldum,MethyloparacoccusandMethylogaeain the familyMethylococcaceae. The similarity was low (94.6 %) between strain RS11D-Pr^Tand the most closely related type strain (Methyloparacoccus murrelliiR-49797^T). The DNA G+C content was 64.1 mol%. Results of phylogenetic analysis of thepmoAgene and chemotaxonomic data regarding the major cellular fatty acids (C_16 : 1ω7c, C_16 : 0and C_14 : 0) and the major respiratory quinone (MQ-8) also indicated the affiliation of strain RS11D-Pr^Tto theMethylococcus–Methylocaldum–Methyloparacoccus–Methylogaeaclade. On the basis of phenotypic, genotypic and phylogenetic characteristics, strain RS11D-Pr^Tis considered to represent a novel genus and species within the familyMethylococcaceae, for which the nameMethylomagnum ishizawaigen. nov., sp. nov. is proposed. The type strain is RS11D-Pr^T( = JCM 18894^T = NBRC 109438^T = DSM 29768^T = KCTC 4681^T).