Unraveling the metabolic mechanisms of pioneer bacteria during the utilization of fresh macroalgae

We cultivated the flavobacterium Zobellia galactanivorans DsijT with fresh brown macroalgae with distinct chemical compositions. Its capacity to use macroalgae as the sole carbon source via the secretion of extracellular enzymes, leading to extensive tissue damages, highlights a sharing pioneer degrader behavior. RNA-seq transcriptome analysis revealed a metabolic shift toward the utilization of brown algal polysaccharides during tissue degradation. A subset of genes was specifically induced in cells grown with intact algae compared to purified polysaccharides. It notably includes genes involved in protection against oxidative burst, type IX secretion system proteins and novel uncharacterized Polysaccharides Utilization Loci (PULs). Comparative growth experiments and genomics between Zobellia members brought out putative genetic determinants of the pioneer behavior of Z. galactanivorans, whose in vitro role could be further characterized. This work constitutes the first investigation of the metabolic mechanisms of bacteria mediating fresh macroalgae breakdown, and will help unravel the role of marine microbes in the fate of macroalgal biomass. RNAseq profiles of Zobellia galactanivorans DsijT when grown with different carbon sources. Profiles of free-living cells were assessed with Laminaria digitata, Fucus serratus, Ascophyllum nodosum, Maltose, Alginate or Fucose-containing sulfated polysaccharides (FCSP) as the sole carbon source. Profiles of algae-attached cells were assessed with Laminaria digitata and Fucus serratus as the sole carbon source. Experiments were done in triplicates for each condition (except for free-living cells with F. serratus and algae-attached cells where n=2). 21 samples in total. Maltose condition was used as a control.