Zobellia alginiliquefaciens sp. nov., a novel member of the flavobacteria isolated from the epibiota of the brown alga Ericaria zosteroides (C. Agardh) Molinari & Guiry 2020

International audienceStrain LLG6346-3.1 T , isolated from the thallus of the brown alga Ericaria zosteroides collected from the Mediterranean Sea near Bastia in Corsica, France, was characterised using a polyphasic method. Cells were Gram-stain-negative, strictly aerobic, non-flagellated, motile by gliding, rod-shaped and grew optimally at 30–33 °C, at pH 8–8.5 and with 4–5 % NaCl. LLG6346-3.1 T used the seaweed polysaccharide alginic acid as a sole carbon source which was vigorously liquefied. The results of phylogenetic analyses indicated that the bacterium is affiliated to the genus Zobellia (family Flavobacteriaceae , class Flavobacteriia ). LLG6346-3.1 T exhibited 16S rRNA gene sequence similarity values of 98.6 and 98.3 % to the type strains of Zobellia russellii and Zobellia roscoffensis , respectively, and of 97.4–98.5 % to members of other species of the genus Zobellia . The DNA G+C content of LLG6346-3.1 T was determined to be 38.3 mol%. Digital DNA–DNA hybridisation predictions by the average nucleotide identity (ANI) and genome to genome distance calculator (GGDC) methods between LLG6346-3.1 T and other members of the genus Zobellia showed values of 76–88 % and below 37 %, respectively. The results of phenotypic, phylogenetic and genomic analyses indicate that LLG6346-3.1 T is distinct from species of the genus Zobellia with validly published names and that it represents a novel species of the genus Zobellia , for which the name Zobellia alginiliquefaciens sp. nov. is proposed. The type strain is LLG6346-3.1 T (= RCC7657 T = LMG 32918 T )

Seasonal dynamics of a glycan‐degrading flavobacterial genus in a tidally mixed coastal temperate habitat

International audienceCoastal marine habitats constitute hotspots of primary productivity. In temperate regions, this is due both to massive phytoplankton blooms and dense colonisation by macroalgae that mostly store carbon as glycans, contributing substantially to local and global carbon sequestration. Because they control carbon and energy fluxes, algae‐degrading microorganisms are crucial for coastal ecosystem functions. Environmental surveys revealed consistent seasonal dynamics of alga‐associated bacterial assemblages, yet resolving what factors regulate the in situ abundance, growth rate and ecological functions of individual taxa remains a challenge. Here, we specifically investigated the seasonal dynamics of abundance and activity for a well‐known alga‐degrading marine flavobacterial genus in a tidally mixed coastal habitat of the Western English Channel. We show that members of the genus Zobellia are a stable, low‐abundance component of healthy macroalgal microbiota and can also colonise particles in the water column. This genus undergoes recurring seasonal variations with higher abundances in winter, significantly associated to biotic and abiotic variables. Zobellia can become a dominant part of bacterial communities on decaying macroalgae, showing a strong activity and high estimated in situ growth rates. These results provide insights into the seasonal dynamics and environmental constraints driving natural populations of alga‐degrading bacteria that influence coastal carbon cycling

Evaluation of a new primer combination to minimize plastid contamination in 16S rDNA metabarcoding analyses of alga‐associated bacterial communities

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Exploration de la diversité des bactéries marines dégradant les macroalgues par marquage isotopique

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Accumulation of detached kelp biomass in a subtidal temperate coastal ecosystem induces succession of epiphytic and sediment bacterial communities.

Kelps are dominant primary producers in temperate coastal ecosystems. Large amounts of kelp biomass can be exported to the seafloor during the algal growth cycle or following storms, creating new ecological niches for the associated microbiota. Here, we investigated the bacterial community associated with the kelp Laminaria hyperborea during its accumulation and degradation on the seafloor. Kelp tissue, seawater and sediment were sampled during a six‐month in situ experiment simulating kelp detritus accumulation. Evaluation of the epiphytic bacterial community abundance, structure, taxonomic composition and predicted functional profiles evidenced a biphasic succession. Initially dominant genera (Hellea, Litorimonas, Granulosicoccus) showed a rapid and drastic decrease in sequence abundance, probably outcompeted by algal polysaccharide‐degraders such as Bacteroidia members which responded within 4 weeks. Acidimicrobiia, especially members of the Sva0996 marine group, colonized the degrading kelp biomass after 11 weeks. These secondary colonizers could act as opportunistic scavenger bacteria assimilating substrates exposed by early degraders. In parallel, kelp accumulation modified bacterial communities in the underlying sediment, notably favoring anaerobic taxa potentially involved in the sulfur and nitrogen cycles. Overall, this study provides insights into the bacterial degradation of algal biomass in situ, an important link in coastal trophic chains

Isotopic tracing reveals single-cell assimilation of a macroalgal polysaccharide by a few marine Flavobacteria and Gammaproteobacteria

International audienceAlgal polysaccharides constitute a diverse and abundant reservoir of organic matter for marine heterotrophic bacteria, central to the oceanic carbon cycle. We investigated the uptake of alginate, a major brown macroalgal polysaccharide, by microbial communities from kelp-dominated coastal habitats. Congruent with cell growth and rapid substrate utilization, alginate amendments induced a decrease in bacterial diversity and a marked compositional shift towards copiotrophic bacteria. We traced 13 C derived from alginate into specific bacterial incorporators and quantified the uptake activity at the single-cell level, using halogen in situ hybridization coupled to nanoscale secondary ion mass spectrometry (HISH-SIMS) and DNA stable isotope probing (DNA-SIP). Cell-specific alginate uptake was observed for Gammaproteobacteria and Flavobacteriales, with carbon assimilation rates ranging from 0.14 to 27.50 fg C µm −3 h −1. DNA-SIP revealed that only a few initially rare Flavobacteriaceae and Alteromonadales taxa incorporated 13 C from alginate into their biomass, accounting for most of the carbon assimilation based on bulk isotopic measurements. Functional screening of metagenomic libraries gave insights into the genes of alginolytic Alteromonadales active in situ. These results highlight the high degree of niche specialization in heterotrophic communities and help constraining the quantitative role of polysaccharide-degrading bacteria in coastal ecosystems