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).

A Deep-Sea Bacterium Senses Blue Light via a BLUF-Dependent Pathway

Light is a ubiquitous energy source and environmental signal that broadly impacts the lifestyle of a large number of photosynthetic/nonphotosynthetic microorganisms living in the euphotic layer. However, the responses of deep-sea microbes to light are largely unknown, even though blue light is proposed to be distributed in the deep ocean. Here, we successfully cultured a novel bacterial species, named Spongiibacter nanhainus CSC3.9, from deep-sea cold seep samples by a blue light induction approach. The growth of strain CSC3.9 was obviously promoted by the illumination of blue light. We next determined BLUF (a typical blue light photoreceptor) was the most essential factor directing light sensing of strain CSC3.9 through a combined proteomic and genetic method. The function of light sensing mediated by BLUF was further confirmed by the in vitro-synthesized protein. Notably, homologs of BLUF widely existed across the marine microorganisms (containing Spongiibacter species) derived from different environments, including cold seeps. This strongly indicates that the distribution of light utilization by the nonphototrophic bacteria living in the ocean is broad and has been substantially underestimated.

IMPORTANCE Extensive studies have been conducted to explore the mechanisms of light sensing and utilization by microorganisms that live in the photic zone. Strikingly, accumulated evidence shows that light is distributed in the deep biosphere. However, the existence and process of light sensing and utilization by microbes inhabiting the deep ocean have been seldom reported. In the present study, a novel bacterial strain, Spongiibacter nanhainus CSC3.9, was enriched and purified from a deep-sea cold seep sample through a blue light induction method. Combined with genomic, proteomic, genetic, and biochemical approaches, the mechanism of this novel strain sensing blue light through a BLUF-dependent pathway was detailed. Our study provides a good model to study the mechanisms of light sensing mediated by deep-sea nonphototrophic bacteria.