Molecular and phenotypic analyses reveal the non-identity of the Phaeobacter gallaeciensis type strain deposits CIP 105210T and DSM 17395

The marine genus Phaeobacter currently comprises six species, some of which were intensively studied mainly due to their ability to produce secondary metabolites. The type strain of the type species, Phaeobacter gallaeciensis BS107T, has been deposited at several public culture collections worldwide. Based on differences in plasmid profiles, we detected that the alleged P. gallaeciensis type strains deposited at the Collection Institute Pasteur (CIP; Paris, France) as CIP 105210 and at the German Collection of Microorganisms and Cell Cultures (DSMZ; Braunschweig, Germany) as DSM 17395 are not identical. To determine the identity of these strains, we conducted DNA–DNA hybridization, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF), 16S rRNA gene and internal transcribed spacer (ITS) sequence analyses, as well as physiological experiments. Based on the detailed 16S rRNA gene reanalysis we showed that strain CIP 105210 most likely corresponds to the original P. gallaeciensis type strain BS107T. In contrast, the Phaeobacter strain DSM 17395 exhibits a much closer affiliation to Phaeobacter inhibens DSM 16374T ( = T5T) and should thus be allocated to this species. The detection of the dissimilarity of strains CIP 105210T and DSM 17395 will influence future comparative studies within the genus Phaeobacter .

Disruption of Cell-to-Cell Signaling Does Not Abolish the Antagonism of Phaeobacter gallaeciensis toward the Fish Pathogen Vibrio anguillarum in Algal Systems

ABSTRACTQuorum sensing (QS) regulatesPhaeobacter gallaeciensisantagonism in broth systems; however, we demonstrate here that QS is not important for antagonism in algal cultures. QS mutants reducedVibrio anguillarumto the same extent as the wild type. Consequently, a combination of probioticPhaeobacterand QS inhibitors is a feasible strategy for aquaculture disease control.

Genetic Analysis of the Upper Phenylacetate Catabolic Pathway in the Production of Tropodithietic Acid by Phaeobacter gallaeciensis

ABSTRACTProduction of the antibiotic tropodithietic acid (TDA) depends on the central phenylacetate catabolic pathway, specifically on the oxygenase PaaABCDE, which catalyzes epoxidation of phenylacetyl-coenzyme A (CoA). Our study was focused on genes of the upper part of this pathway leading to phenylacetyl-CoA as precursor for TDA.Phaeobacter gallaeciensisDSM 17395 encodes two genes with homology to phenylacetyl-CoA ligases (paaK1andpaaK2), which were shown to be essential for phenylacetate catabolism but not for TDA biosynthesis and phenylalanine degradation. Thus, inP. gallaeciensisanother enzyme must produce phenylacetyl-CoA from phenylalanine. Using random transposon insertion mutagenesis of apaaK1-paaK2double mutant we identified a gene (ior1) with similarity toiorAandiorBin archaea, encoding an indolepyruvate:ferredoxin oxidoreductase (IOR). Theior1mutant was unable to grow on phenylalanine, and production of TDA was significantly reduced compared to the wild-type level (60%). Nuclear magnetic resonance (NMR) spectroscopic investigations using13C-labeled phenylalanine isotopomers demonstrated that phenylalanine is transformed into phenylacetyl-CoA by Ior1. Using quantitative real-time PCR, we could show that expression ofior1depends on the adjacent regulator IorR. Growth on phenylalanine promotes production of TDA, induces expression ofior1(27-fold) andpaaK1(61-fold), and regulates the production of TDA. Phylogenetic analysis showed that the aerobic type of IOR as found in many roseobacters is common within a number of different phylogenetic groups of aerobic bacteria such asBurkholderia,Cupriavidis, andRhizobia, where it may also contribute to the degradation of phenylalanine.