Shell Disease Syndrome Is Associated with Reduced and Shifted Epibacterial Diversity on the Carapace of the Crustacean Cancer pagurus

Cancer pagurus is highly susceptible to shell disease syndrome. However, little is known about concomitant changes in the epibacterial community. We compared the bacterial communities of black spot affected and nonaffected areas of the carapace by amplicon sequencing of 16S rRNA genes and 16S rRNA. Within each spot, bacterial communities of affected areas were less diverse compared to communities from nonaffected areas. Communities of different affected spots were, however, more divergent from each other, compared to those of different nonaffected areas. This indicates a reduced and shifted microbial community composition caused by the black spot disease. Different communities found in black spots likely indicate different stages of the disease. In affected areas, Flavobacteriaceae rose to one of the most abundant and active families due to the increase of Aquimarina spp., suggesting a significant role in shell disease syndrome. We isolated 75 bacterial strains from diseased and healthy areas, which are primarily affiliated with Proteobacteria and Bacteroidetes, reflecting the dominant phyla detected by amplicon sequencing. The ability to degrade chitin was mainly found for Gammaproteobacteria and Aquimarina spp. within the Flavobacteriia, while the ability to use N-acetylglucosamine, the monomer of the polysaccharide chitin, was observed for most isolates, including many Alphaproteobacteria. One-third of the isolates, including most Aquimarina spp., showed antagonistic properties, indicating a high potential for interactions between the bacterial populations. The combination of bacterial community analysis and the physiological properties of the isolates provided insights into a functional complex epibacterial community on the carapace of C. pagurus. IMPORTANCE In recent years, shell disease syndrome has been detected for several ecologically and economically important crustacean species. Large proportions of populations are affected, e.g., >60% of the widely distributed species Cancer pagurus in different North Sea areas. Bacteria play a significant role in the development of different forms of shell disease, all characterized by microbial chitinolytic degradation of the outer shell. By comparing the bacterial communities of healthy and diseased areas of the shell of C. pagurus, we demonstrated that the disease causes a reduced bacterial diversity within affected areas, a phenomenon co-occurring also with many other diseases. Furthermore, the community composition dramatically changed with some taxa rising to high relative abundances and showing increased activity, indicating strong participation in shell disease. Characterization of bacterial isolates obtained from affected and nonaffected spots provided deeper insights into their physiological properties and thus the possible role within the microbiome.

Metabolism of 2,3-dihydroxypropane-1-sulfonate by marine bacteria

Both enantiomers of the sulfoquinovose breakdown product 2,3-dihydroxypropane-1-sulfonate, an important sulfur metabolite produced by marine algae, were synthesised in a ³⁴S-labelled form and used in feeding experiments with marine bacteria. The labelling was efficiently incorporated into the sulfur-containing antibiotic tropodithietic acid and sulfur volatiles by the algal symbiont Phaeobacter inhibens, but not into sulfur volatiles released by marine bacteria associated with crustaceans. The ecological implications and the relevance of these findings for the global sulfur cycle are discussed.

Rhodobacteraceae on the marine brown alga Fucus spiralis are abundant and show physiological adaptation to an epiphytic lifestyle

Macroalgae harbour specific microbial communities on their surface that have functions related to host health and defence. In this study, the bacterial biofilm of the marine brown alga Fucus spiralis was investigated using 16S rRNA gene amplicon-based analysis and isolation of bacteria. Rhodobacteraceae (Alphaproteobacteria) were the predominant family constituting 23% of the epibacterial community. At the genus level, Sulfitobacter, Loktanella, Octadecabacter and a previously undescribed cluster were most abundant, and together they comprised 89% of the Rhodobacteraceae. Supported by a specific PCR approach, 23 different Rhodobacteraceae-affiliated strains were isolated from the surface of F. spiralis, which belonged to 12 established and three new genera. For seven strains, closely related sequences were detected in the 16S rRNA gene dataset. Growth experiments with substrates known to be produced by Fucus spp. showed that all of them were consumed by at least three strains, and vitamin B12 was produced by 70% of the isolates. Since growth of F. spiralis depends on B12 supplementation, bacteria may provide the alga with this vitamin. Most strains produced siderophores, which can enhance algal growth under iron-deficient conditions. Inhibiting properties against other bacteria were only observed when F. spiralis material was present in the medium. Thus, the physiological properties of the isolates indicated adaption to an epiphytic lifestyle.

Pathways and substrate-specific regulation of amino acid degradation in Phaeobacter inhibens DSM 17395 (archetype of the marine Roseobacter clade)

Combining omics and enzymatic approaches, catabolic routes of nine selected amino acids (tryptophan, phenylalanine, methionine, leucine, isoleucine, valine, histidine, lysine and threonine) were elucidated in substrate-adapted cells of Phaeobacter inhibens DSM 17395 (displaying conspicuous morphotypes). The catabolic network [excluding tricarboxylic acid (TCA) cycle] was reconstructed from 71 genes (scattered across the chromosome; one-third newly assigned), with 69 encoded proteins and 20 specific metabolites identified, and activities of 10 different enzymes determined. For example, Ph. inhibens DSM 17395 does not degrade lysine via the widespread saccharopine pathway but might rather employ two parallel pathways via 5-aminopentanoate or 2-aminoadipate. Tryptophan degradation proceeds via kynurenine and 2-aminobenzoate; the latter is metabolized as known from Azoarcus evansii. Histidine degradation is analogous to the Pseudomonas-type Hut pathway via N-formyl-l-glutamate. For threonine, only one of the three genome-predicted degradation pathways (employing threonine 3-dehydrogenase) is used. Proteins of the individual peripheral degradation sequences in Ph. inhibens DSM 17395 were apparently substrate-specifically formed contrasting the non-modulated TCA cycle enzymes. Comparison of genes for the reconstructed amino acid degradation network in Ph. inhibens DSM 17395 across 27 other complete genomes of Roseobacter clade members revealed most of them to be widespread among roseobacters.