Publications

4855

Summary The anaerobic, mesophilic and moderately halophilic strain L21‐Spi‐D4 T was recently isolated from the suboxic zone of a hypersaline cyanobacterial mat using protein‐rich extracts of Arthrospira (formerly Spirulina ) platensis as substrate. Phylogenetic analyses based on 16S rRNA genes indicated an affiliation of the novel strain with the Bacteroidetes clade MgMjR‐022, which is widely distributed and abundant in hypersaline microbial mats and heretofore comprised only sequences of uncultured bacteria. Analyses of the complete genome sequence of strain L21‐Spi‐D4 T revealed a possible specialization on the degradation of cyanobacterial biomass. Besides genes for enzymes degrading specific cyanobacterial proteins a conspicuous transport complex for the polypeptide cyanophycin could be identified that is homologous to typical polysaccharide utilization loci of Bacteroidetes . A distinct and reproducible co‐occurrence pattern of environmental 16S rRNA gene sequences of the MgMjR‐022 clade and cyanobacteria in the suboxic zone of hypersaline mats points to a specific dependence of members of this clade on decaying cyanobacteria. Based on a comparative analysis of phenotypic, genomic and ecological characteristics we propose to establish the novel taxa Salinivirga cyanobacteriivorans gen. nov., sp. nov., represented by the type strain L21‐Spi‐D4 T , and Salinivirgaceae fam. nov., comprising sequences of the MgMjR‐022 clade.

Abstract Mealybugs (Insecta: Hemiptera: Pseudococcidae) maintain obligatory relationships with bacterial symbionts, which provide essential nutrients to their insect hosts. Most pseudococcinae mealybugs harbor a unique symbiosis setup with enlarged betaproteobacterial symbionts (‘Candidatus Tremblaya princeps’), which themselves contain gammaproteobacterial symbionts. Here we investigated the symbiosis of the manna mealybug, Trabutina mannipara, using a metagenomic approach. Phylogenetic analyses revealed that the intrabacterial symbiont of T. mannipara represents a novel lineage within the Gammaproteobacteria, for which we propose the tentative name ‘Candidatus Trabutinella endobia’. Combining our results with previous data available for the nested symbiosis of the citrus mealybug Planococcus citri, we show that synthesis of essential amino acids and vitamins and translation-related functions partition between the symbiotic partners in a highly similar manner in the two systems, despite the distinct evolutionary origin of the intrabacterial symbionts. Bacterial genes found in both mealybug genomes and complementing missing functions in both symbioses were likely integrated in ancestral mealybugs before T. mannipara and P. citri diversified. The high level of correspondence between the two mealybug systems and their highly intertwined metabolic pathways are unprecedented. Our work contributes to a better understanding of the only known intracellular symbiosis between two bacteria and suggests that the evolution of this unique symbiosis included the replacement of intrabacterial symbionts in ancestral mealybugs.