Environmental Microbiology

SummaryKnowledge of intraspecific variation in symbioses may aid in understanding the ecology of widespread insects in different parts of their range. We investigated bacterial symbionts of Adelges tsugae, a pest of hemlocks in eastern North America introduced from Asia. Amplification, cloning, and sequencing of bacterial 16S rDNA, in situ hybridizations, and electron microscopy revealed that A. tsugae harbours up to five bacterial phylotypes, according to population. Three Gammaproteobacteria species are maternally transmitted. The first, designated ‘Ca. Pseudomonas adelgestsugas’ resides in the haemocoel, and was detected in all populations except Taiwan. The second phylotype, ‘Ca. Serratia symbiotica’, resides in bacteriocytes of populations on Tsuga sieboldii in Japan and in E. North America. The third phylotype, designated ‘Ca. Annandia adelgestsuga’, clustered within a lineage of several insect endosymbionts that included Buchnera aphidicola. It was detected in bacteriocytes in all populations, and in salivary glands of first instars. Two Betaproteobacteria phylotypes were detected in some Japanese T. sieboldii and eastern North America populations, and were observed only in salivary glands with no evidence of maternal transmission. Our results support the ideas that symbiont gain and loss has been volatile in adelgids, and that symbionts may help to trace the source of invasive species.

SummaryA novel moderately thermophilic, facultatively anaerobic chemoorganotrophic bacterium strainP3M‐2Twas isolated from a microbial mat developing on the wooden surface of a chute under the flow of hot water (46°C) coming out of a 2775‐m‐deep oil exploration well (Tomsk region,Russia). StrainP3M‐2Tis a moderate thermophile and facultative anaerobe growing on mono‐, di‐ or polysaccharides by aerobic respiration, fermentation or by reducing diverse electron acceptors [nitrite,Fe(III),As(V)]. Its closest cultivated relative (90.8%rRNAgene sequence identity) isIgnavibacterium album, the only chemoorganotrophic member of the phylumChlorobi. New genus and speciesMelioribacter roseusare proposed for isolateP3M‐2T. Together withI. album, the new organism represents the classIgnavibacteriaassigned to the phylumChlorobi. The revealed group includes a variety of uncultured environmental clones, the16S rRNAgene sequences of some of which have been previously attributed to the candidate divisionZB1. Phylogenetic analysis ofM. roseusandI. albumbased on their23S rRNAandRecAsequences confirmed that these two organisms could represent an even deeper, phylum‐level lineage. Hence, we propose a new phylumIgnavibacteriaewithin theBacteroidetes–Chlorobigroup with a sole classIgnavibacteria, two familiesIgnavibacteriaceaeandMelioribacteraceaeand two speciesI. albumandM. roseus. This proposal correlates with chemotaxonomic data and phenotypic differences of both organisms from other cultured representatives ofChlorobi. The most essential differences, supported by the analyses of complete genomes of both organisms, are motility, facultatively anaerobic and obligately organotrophic mode of life, the absence of chlorosomes and the apparent inability to grow phototrophically.