Pseudomonas fungipugnans sp. nov., a potently antifungal bacterium isolated from moss.

Abstract

A novel strain, 681, was isolated from a moss sample taken from the Chrutzelried woods in Canton Zürich, Switzerland. The strain showed potent activity against several fungi and oomycetes. It was affiliated to the Pseudomonas genus by 16S rRNA gene sequence phylogeny. Genome sequencing showed a G+C content of 59.9 mol%. The highest average nucleotide identity was 86.63%, and the highest digital DNA-DNA hybridization value was 32.2% (with Pseudomonas nunensis ln5), considerably below the thresholds for species delineation. Multi-locus phylogeny using 81 concatenated sequences indicated that the strain represented a new species within the Pseudomonas mandelii subgroup. This study details its characterization as a new species. The 681 genome was screened in silico using antiSMASH to reveal candidate secondary metabolite clusters for the strong antifungal activity exhibited by 681. Of the 15 clusters identified, we disrupted the seven best and tested for activity against Fusarium solani. The pyrrolnitrin, rhizoxin, novel PKS-NRPS and acaterin gene clusters contributed significantly to the observed antifungal activity. Phenotypic analyses found that strain 681 cells were aerobic, Gram-negative, motile rods (mean length 2.60 µm and mean width of 0.67 µm) with one to three polar flagella. Optimal growth was at 30 °C, but growth also occurred at 8 °C. The pH range was 6-7, with some growth at pH 8. Robust growth occurred at 0-3% (w/v) NaCl and weak growth at 4% (w/v) NaCl, with the optimum at 1% (w/v) NaCl. Strain 681 was oxidase positive, hydrolysed arginine under anaerobic conditions, showed intense fluorescence on King's medium B and produced a hypersensitive response in tobacco leaves. Following our investigations, we propose the designation Pseudomonas fungipugnans sp. nov. for this new species. The type strain, 681, is available from the DSMZ and LMG/BCCM culture collections under the designations DSM 115721 and LMG 33039, respectively.