Proposal of Zooshikellaceae fam. nov. to accommodate the genera Zooshikella and Spartinivicinus and reclassification of Zooshikella marina as a later heterotypic synonym of Zooshikella ganghwensis based on whole genome sequence analysis

Abstract

The genus Spartinivicinus , affiliated to the class Gammaproteobacteria , is an important marine member that produces prodiginines. Currently, its taxonomic assignment to family level is not well presented. Phylogeny of 16S rRNA gene sequences indicated that Spartinivicinus forms a monophyletic clade with Zooshikella , which is neighboured by Aestuariirhabdus of the family Aestuariirhabdaceae and another monophyletic clade of the family Endozoicomonadaceae . The 16S rRNA gene of Spartinivicinus ruber S2-4-1HT had sequence similarities to those of Aestuariirhabdus litorea GTF13T, Zooshikella members and Endozoicomonas members of 93.4%, 93.2–93.4  and <92.5 %, respectively. Phylogenomic analysis based on 120 bacterial conserved single-copy genes highly supported placing Spartinivicinus as a sister member of Zooshikella , neighboured by Aestuariirhabdaceae and Endozoicomonadaceae members, indicating that Spartinivicinus and Zooshikella could be considered to belong to the same family. Thus, Zooshikellaceae fam. nov. is proposed to accommodate the two genera. Colonies of Spartinivicinus and Zooshikella are red-pigmented, which is different from Aestuariirhabdus (pale-yellow pigmented). The major respiratory quinone of S. ruber was ubiquinone (Q-9), similar to Zooshikella , but distinct from Aestuariirhabdus (Q-9 and Q-8). The predominant fatty acids and polar lipids of Spartinivicinus also showed a similar patterns to Zooshikella , but they were different from Aestuariirhabdus . Lastly, Spartinivicinus possessed a genome size of 6.68 Mbp and DNA G+C content of 40.1mol%, similar to Zooshikella , but much larger than Aestuariirhabdus . In addition, the 16S rRNA genes of Z. ganghwensis JC2044T and Z. marina JC333T possess sequence similarity of 99.79 %. Whole genome comparisons indicated that they shared 79.8 % digital DNA–DNA hybridization, 97.78 % average nucleotide identity and 97.31 % average amino acid identity values. Activities of catalase and oxidase for the two strains were positive. Hydrolysis of skimmed milk and Tweens (40, 60 and 80) was positive. Interestingly, the two strains produced different kinds of prodiginines. We propose that Z. marina is a later heterotypic synonym of Zooshikella ganghwensis .