Genomic analysis reveals versatile heterotrophic capacity of a potentially symbiotic sulfur-oxidizing bacterium in sponge.

Sulfur-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB) play essential roles in marine sponges. However, the detailed characteristics and physiology of the bacteria are largely unknown. Here, we present and analyse the first genome of sponge-associated SOB using a recently developed metagenomic binning strategy. The loss of transposase and virulence-associated genes and the maintenance of the ancient polyphosphate glucokinase gene suggested a stabilized SOB genome that might have coevolved with the ancient host during establishment of their association. Exclusive distribution in sponge, bacterial detoxification for the host (sulfide oxidation) and the enrichment for symbiotic characteristics (genes-encoding ankyrin) in the SOB genome supported the bacterial role as an intercellular symbiont. Despite possessing complete autotrophic sulfur oxidation pathways, the bacterium developed a much more versatile capacity for carbohydrate uptake and metabolism, in comparison with its closest relatives (Thioalkalivibrio) and to other representative autotrophs from the same order (Chromatiales). The ability to perform both autotrophic and heterotrophic metabolism likely results from the unstable supply of reduced sulfur in the sponge and is considered critical for the sponge-SOB consortium. Our study provides insights into SOB of sponge-specific clade with thioautotrophic and versatile heterotrophic metabolism relevant to its roles in the micro-environment of the sponge body.

Rheinheimera nanhaiensis sp. nov., isolated from marine sediments, and emended description of the genus Rheinheimera Brettar et al. 2002 emend. Merchant et al. 2007.

A Gram-negative, facultatively aerobic, oxidase- and catalase-positive, rod-shaped bacterium, designated strain E407-8(T), was isolated from a sediment sample from the South China Sea. Phylogenetic analysis of the 16S rRNA gene sequence revealed that strain E407-8(T) was affiliated with the genus Rheinheimera, sharing the highest sequence similarity with Rheinheimera pacifica KMM 1406(T) (97.5 %) and Rheinheimera aquimaris SW-353(T) (97.4 %) and showing less than 97 % sequence similarity to the type strains of other recognized Rheinheimera species. Levels of DNA-DNA relatedness of strain E407-8(T) to R. pacifica DSM 17616(T) and R. aquimaris JCM 14331(T) were 25.2 % (25.3 % in the duplicate measurement) and 9.4 % (6.5 %), respectively. The bacterium could grow at 10-48 °C (optimum 37 °C) and in the presence of 0-8 % (w/v) NaCl (optimum 0.5-2.5 %). The major cellular fatty acids of strain E407-8(T) were summed feature 3 (C(16 : 1)ω7c and/or iso-C(15 : 0) 2-OH), C(17 : 1)ω8c, C(16 : 0) and C(18 : 1)ω7c. The predominant respiratory quinone was ubiquinone Q-8. The DNA G+C content was 51.0 mol%. Based on the results of our polyphasic taxonomic study, strain E407-8(T) represents a novel species in the genus Rheinheimera, for which the name Rheinheimera nanhaiensis sp. nov. is proposed. The type strain is E407-8(T) ( = CCTCC AB 209089(T)  = KACC 14030(T)). An emended description of the genus Rheinheimera Brettar et al. 2002 emend. Merchant et al. 2007 is also proposed.

Neptunomonas antarctica sp. nov., isolated from marine sediment.

A Gram-negative, motile, oxidase- and catalase-positive and facultatively aerobic bacterium, designated S3-22T, was isolated from marine sediment of the Nella Fjord, Antarctica. Strain S3-22T reduced nitrate to nitrite and grew at pH 6.0-8.0, at 4-25 degrees C and with 0.5-5% (w/v) NaCl. It contained Q-8 as the only respiratory quinone and summed feature 3 (C16:1omega7c and/or iso-C15:0 2-OH), C16:0 and C18:1omega7c as the major cellular fatty acids. The genomic DNA G+C content was 45.6 mol%. Phylogenetic analyses of 16S rRNA gene sequences showed that strain S3-22T was affiliated with the genus Neptunomonas, with 97.1% sequence similarity to Neptunomonas japonica JAMM 0745T and 94.8% to Neptunomonas naphthovorans NAG-2N-126T, the type strains of the only two recognized Neptunomonas species. DNA-DNA relatedness between strain S3-22T and N. japonica JCM 14595T was 20.4%. Strain S3-22T could be distinguished from the type strains of Neptunomonas species by several phenotypic properties. Based on the evidence from our polyphasic study, strain S3-22T represents a novel Neptunomonas species, for which the name Neptunomonas antarctica sp. nov. is proposed. The type strain is S3-22T (=CCTCC AB 209086T =KACC 14056T).