Spongiibacter pelagi sp. nov., a marine gammaproteobacterium isolated from coastal seawater

Identification of bacteria in potential mutualism with toxic Alexandrium catenella in Chilean Patagonian fjords by in vitro and field monitoring

The dinoflagellate Alexandrium catenella is a well-known paralytic shellfish toxin producer that forms harmful algal blooms, repeatedly causing damage to Chilean coastal waters. The causes and behavior of algal blooms are complex and vary across different regions. As bacterial interactions with algal species are increasingly recognized as a key factor driving algal blooms, the present study identifies several bacterial candidates potentially associated with Chilean Alexandrium catenella. This research narrowed down the selection of bacteria from the Chilean A. catenella culture using antibiotic treatment and 16S rRNA metabarcoding analysis. Subsequently, seawater from two Chilean coastal stations, Isla Julia and Isla San Pedro, was monitored for two years to detect Alexandrium species and the selected bacteria, utilizing 16S and 18S rRNA gene metabarcoding analyses. The results suggested a potential association between Alexandrium species and Spongiibacteraceae at both stations. The proposed candidate bacteria within the Spongiibacteraceae family, potentially engaging in mutualistic relationships with Alexandrium species, included the genus of BD1-7 clade, Spongiibbacter, and Zhongshania.

Marortus luteolus Yu et al. 2019 is a later heterotypic synonym of Zhongshania marina On et al. 2019

Phylogeny of 16S rRNA gene sequences showed that Marortus luteolus ZX-21T and Zhongshania marina DSW25-10T are closely related, and form a monophyletic clade affiliated with the genus Zhongshania. Whole genome sequence comparisons showed that M. luteolus ZX-21T and Z. marina DSW25-10T shared 78.8 % digital DNA-DNA hybridization, 97.6 % average nucleotide identity and 98.1 % average amino acid identity. These values exceeded the recommended threshold values for species delineation. Thus, based on the principle of priority, we propose the reclassification of Marortus luteolus Yu et al. 2019 as a later heterotypic synonym of Zhongshania marina On et al. 2019.

Spongiibacter thalassae sp. nov., a marine gammaproteobacterium isolated from seawater

A bacterium, designated as KMU-166^T, belonging to the class Gammaproteobacteria, was isolated from seawater collected on the coastline of Dadaepo, Republic of Korea. Strain KMU-166^T was Gram-staining-negative, ovoid-shaped, motile, strictly aerobic, beige-colored, catalase-positive, and oxidase-negative; and had a chemoorganoheterotrophic metabolism. The novel isolate was found to grow at 1-4% NaCl concentrations (w/v), pH 6.5-9.5, and 10-40 °C. The 16S rRNA gene sequence-based phylogeny showed that strain KMU-166^T affiliates to the family Spongiibacteraceae and that it shared the greatest sequence similarity (96.4%) with Spongiibacter marinus HAL40b^T. The main (> 10%) cellular fatty acids were summed feature 3 (C16:1ω7c and/or C16:1ω6c), C17:1ω8c, and C18:1ω7c. The predominant respiratory quinone was ubiquinone-8 (Q-8). Strain KMU-166^T comprised phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, and two unidentified lipids. The assembled draft genome was 4.40 Mbp in size with a DNA G+C content of 55.7%. The average nucleotide identity, digital DNA-DNA hybridization, and average amino acid identity values of KMU-166^T and Spongiibacter marinus HAL40b^T, Spongiibacter tropicus CL-CB221^T, and "Spongiibacter pelagi" KMU-158^T were found to be 77.7-79.8%, 13.7-15.4%, and 66.1-70.9%, respectively. From the distinguishable polyphasic taxonomic results obtained, the strain is considered to represent a novel species of the genus Spongiibacter for which the name Spongiibacter thalassae sp. nov. is proposed. The type strain of S. thalassae sp. nov. is KMU-166^T (= KCCM 90449^T = NBRC 114308^T).