Description of Spongorhabdus gen. nov., a novel genus within the Endozoicomonadaceae family, and its type species Spongorhabdus nitratireducens sp. nov., isolated from marine sponges

Marine sponges host diverse microbial communities that play essential roles in nutrient cycling and host health. During a study of the microbiota of marine sponges from Taiwan, two Gram-stain-negative, motile and facultatively anaerobic strains, XeTr1^T and StTr2, were isolated from <i>Xestospongia</i> sp. and <i>Stylissa carteri</i>, respectively. Cells were rod-shaped and showed catalase and oxidase activities. Growth was observed at 15-37 °C, pH 6.0-9.0 and 1.0-3.0% (w/v) NaCl. Strains XeTr1^T and StTr2 contained ubiquinone-8 and ubiquinone-9 as major quinones and summed feature 3 (C_16:1 <i> ω7c</i>), summed features 8 (C_18:1 <i> ω7c</i>) and C_16:0 as major fatty acids. The major polar lipids identified in strains XeTr1^T and StTr2 were phosphatidylethanolamine and phosphatidylglycerol. Phylogenetic analysis based on the 16S rRNA gene sequence placed strains XeTr1^T and StTr2 within the family <i>Endozoicomonadaceae</i>, forming a distinct lineage that shared 94% or less sequence homology with its closest relatives, including <i>Endozoicomonas lisbonensis</i> NE40^T, <i>Endozoicomonas arenosclerae</i> CBAS 572^T and <i>Endozoicomonas montiporae</i> CL-33^T. The average amino acid identity values were below the cutoff range for species of the same genus, supporting the placement of strains XeTr1^T and StTr2 as representing a novel genus within the family <i>Endozoicomonadaceae</i>. Distinct phenotypic and chemotaxonomic characteristics, combined with low sequence similarity and a clear phylogenetic separation from known genera, support the proposal of a novel genus and species in the family <i>Endozoicomonadeae</i>, for which the name <i>Spongorhabdus nitratireducens</i> gen. nov., sp. nov. is proposed. The type strain is XeTr1^T (=JCM 37577^T=UCCCB 249^T).