Hasllibacter halocynthiae gen. nov., sp. nov., a nutriacholic acid-producing bacterium isolated from the marine ascidian Halocynthia roretzi

Symbiotic Associations in Ascidians: Relevance for Functional Innovation and Bioactive Potential

Associations between different organisms have been extensively described in terrestrial and marine environments. These associations are involved in roles as diverse as nutrient exchanges, shelter or adaptation to adverse conditions. Ascidians are widely dispersed marine invertebrates associated to invasive behaviours. Studying their microbiomes has interested the scientific community, mainly due to its potential for bioactive compounds production-e.g., ET-73 (trabectedin, Yondelis), an anticancer drug. However, these symbiotic interactions embrace several environmental and biological functions with high ecological relevance, inspiring diverse biotechnological applications. We thoroughly reviewed microbiome studies (microscopic to metagenomic approaches) of around 171 hosts, worldwide dispersed, occurring at different domains of life (Archaea, Bacteria, Eukarya), to illuminate the functions and bioactive potential of associated organisms in ascidians. Associations with Bacteria are the most prevalent, namely with Cyanobacteria, Proteobacteria, Bacteroidetes, Actinobacteria and Planctomycetes phyla. The microbiomes of ascidians belonging to Aplousobranchia order have been the most studied. The integration of worldwide studies characterizing ascidians' microbiome composition revealed several functions including UV protection, bioaccumulation of heavy metals and defense against fouling or predators through production of natural products, chemical signals or competition. The critical assessment and characterization of these communities is extremely valuable to comprehend their biological/ecological role and biotechnological potential.

Biological and Chemical Diversity of Ascidian-Associated Microorganisms

Ascidians are a class of sessile filter-feeding invertebrates, that provide unique and fertile niches harboring various microorganisms, such as bacteria, actinobacteria, cyanobacteria and fungi. Over 1000 natural products, including alkaloids, cyclic peptides, and polyketides, have been isolated from them, which display diverse properties, such as antibacterial, antifungal, antitumor, and anti-inflammatory activities. Strikingly, direct evidence has confirmed that ~8% of natural products from ascidians are actually produced by symbiotic microorganisms. In this review, we present 150 natural products from microorganisms associated with ascidians that have been reported up to 2017.

Limibaculum halophilum gen. nov., sp. nov., a new member of the family Rhodobacteraceae

A Gram-stain-negative, cream-pigmented, aerobic, non-motile, non-spore-forming and short-rod-shaped bacterial strain, designated CAU 1123^T, was isolated from mud from reclaimed land. The strain's taxonomic position was investigated by using a polyphasic approach. Strain CAU 1123^T grew optimally at 37 °C and at pH 7.5 in the presence of 2 % (w/v) NaCl. Phylogenetic analysis based on the 16S rRNA gene sequence revealed that strain CAU 1123^T formed a monophyletic lineage within the family Rhodobacteraceae with 93.8 % or lower sequence similarity to representatives of the genera Rubrimonas, Oceanicella, Pleomorphobacterium, Rhodovulum and Albimonas. The major fatty acids were C18 : 1 ω7c and 11-methyl C18 : 1 ω7c and the predominant respiratory quinone was Q-10. The polar lipids were phosphatidylethanolamine, phosphatidylglycerol, two unidentified phospholipids, one unidentified aminolipid and one unidentified lipid. The DNA G+C content was 71.1 mol%. Based on the data from phenotypic, chemotaxonomic and phylogenetic studies, it is proposed that strain CAU 1123^T represents a novel genus and novel species of the family Rhodobacteraceae, for which the name Limibaculumhalophilum gen. nov., sp. nov. The type strain is CAU 1123^T (=KCTC 52187^T, =NBRC 112522^T).

Development of loop-mediated isothermal amplification targeting 18s ribosomal DNA for rapid detection of Azumiobodo hoyamushi (Kinetoplastea)

Ascidian soft tunic syndrome (AsSTS) caused by Azumiobodo hoyamushi (A. hoyamushi) is a serious aquaculture problem that results in mass mortality of ascidians. Accordingly, the early and accurate detection of A. hoyamushi would contribute substantially to disease management and prevention of transmission. Recently, the loop-mediated isothermal amplification (LAMP) method was adopted for clinical diagnosis of a range of infectious diseases. Here, the authors describe a rapid and efficient LAMP-based method targeting the 18S rDNA gene for detection of A. hoyamushi using ascidian DNA for the diagnosis of AsSTS. A. hoyamushi LAMP assay amplified the DNA of 0.01 parasites per reaction and detected A. hoyamushi in 10 ng of ascidian DNA. To validate A. hoyamushi 18S rDNA LAMP assays, AsSTS-suspected and non-diseased ascidians were examined by microscopy, PCR, and by using the LAMP assay. When PCR was used as a gold standard, the LAMP assay showed good agreement in terms of sensitivity, positive predictive value (PPV), and negative predictive value (NPV). In the present study, a LAMP assay based on directly heat-treated samples was found to be as efficient as DNA extraction using a commercial kit for detecting A. hoyamushi. Taken together, this study shows the devised A. hoyamushi LAMP assay could be used to diagnose AsSTS in a straightforward, sensitive, and specific manner, that it could be used for forecasting, surveillance, and quarantine of AsSTS.

Two new cholic acid derivatives from the marine ascidian-associated bacterium Hasllibacter halocynthiae

The investigation of secondary metabolites in liquid cultures of a recently discovered marine bacterium, Hasllibacter halocynthiae strain KME 002^T, led to the isolation of two new cholic acid derivatives. The structures of these compounds were determined to be 3,3,12-trihydroxy-7-ketocholanic acid (1) and 3,3,12-trihydroxy-7-deoxycholanic acid (2) through HRFABMS and NMR data analyses.