RT Journal Article SR Electronic(1) A1 Becerra-Rivera, Victor A. A1 Arteaga, Alejandra A1 Leija, Alfonso A1 Hernández, Georgina A1 Dunn, Michael F.YR 2020 T1 Polyamines produced by Sinorhizobium meliloti Rm8530 contribute to symbiotically relevant phenotypes ex planta and to nodulation efficiency on alfalfa JF Microbiology, VO 166 IS 3 SP 278 OP 287 DO https://doi.org/10.1099/mic.0.000886 PB Microbiology Society, SN 1465-2080, AB In nitrogen-fixing rhizobia, emerging evidence shows significant roles for polyamines in growth and abiotic stress resistance. In this work we show that a polyamine-deficient ornithine decarboxylase null mutant (odc2) derived from Sinorhizobium meliloti Rm8530 had significant phenotypic differences from the wild-type, including greatly reduced production of exopolysaccharides (EPS; ostensibly both succinoglycan and galactoglucan), increased sensitivity to oxidative stress and decreased swimming motility. The introduction of the odc2 gene borne on a plasmid into the odc2 mutant restored wild-type phenotypes for EPS production, growth under oxidative stress and swimming. The production of calcofluor-binding EPS (succinoglycan) by the odc2 mutant was also completely or mostly restored in the presence of exogenous spermidine (Spd), norspermidine (NSpd) or spermine (Spm). The odc2 mutant formed about 25 % more biofilm than the wild-type, and its ability to form biofilm was significantly inhibited by exogenous Spd, NSpd or Spm. The odc2 mutant formed a less efficient symbiosis with alfalfa, resulting in plants with significantly less biomass and height, more nodules but less nodule biomass, and 25 % less nitrogen-fixing activity. Exogenously supplied Put was not able to revert these phenotypes and caused a similar increase in plant height and dry weight in uninoculated plants and in those inoculated with the wild-type or odc2 mutant. We discuss ways in which polyamines might affect the phenotypes of the odc2 mutant., UL https://www.microbiologyresearch.org/content/journal/micro/10.1099/mic.0.000886