Applied Microbiology and Biotechnology

ABSTRACT Bacterial endosymbionts of the pine bark adelgid, Pineus strobi (Insecta: Hemiptera: Adelgidae), were investigated using transmission electron microscopy, 16S and 23S rRNA-based phylogeny, and fluorescence in situ hybridization. Two morphologically different symbionts affiliated with the Gammaproteobacteria were present in distinct bacteriocytes. One of them (“ Candidatus Annandia pinicola”) is most closely related to an endosymbiont of Adelges tsugae , suggesting that they originate from a lineage already present in ancient adelgids before the hosts diversified into the two major clades, Adelges and Pineus . The other P. strobi symbiont (“ Candidatus Hartigia pinicola”) represents a novel symbiont lineage in members of the Adelgidae. Our findings lend further support for a complex evolutionary history of the association of adelgids with a phylogenetically diverse set of bacterial symbionts.

ABSTRACT A gammaproteobacterial facultative symbiont of the genus Rickettsiella was recently identified in the pea aphid, Acyrthosiphon pisum . Infection with this symbiont altered the color of the aphid body from red to green, potentially affecting the host's ecological characteristics, such as attractiveness to different natural enemies. In European populations of A. pisum , the majority of Rickettsiella -infected aphids also harbor another facultative symbiont, of the genus Hamiltonella . We investigated this Rickettsiella symbiont for its interactions with the coinfecting Hamiltonella symbiont, its phenotypic effects on A. pisum with and without Hamiltonella coinfection, and its infection prevalence in A. pisum populations. Histological analyses revealed that coinfecting Rickettsiella and Hamiltonella exhibited overlapping localizations in secondary bacteriocytes, sheath cells, and hemolymph, while Rickettsiella -specific localization was found in oenocytes. Rickettsiella infections consistently altered hosts' body color from red to green, where the greenish hue was affected by both host and symbiont genotypes. Rickettsiella - Hamiltonella coinfections also changed red aphids to green; this greenish hue tended to be enhanced by Hamiltonella coinfection. With different host genotypes, Rickettsiella infection exhibited either weakly beneficial or nearly neutral effects on host fitness, whereas Hamiltonella infection and Rickettsiella - Hamiltonella coinfection had negative effects. Despite considerable frequencies of Rickettsiella infection in European and North American A. pisum populations, no Rickettsiella infection was detected among 1,093 insects collected from 14 sites in Japan. On the basis of these results, we discuss possible mechanisms for the interaction of Rickettsiella with other facultative symbionts, their effects on their hosts' phenotypes, and their persistence in natural host populations. We propose the designation “ Candidatus Rickettsiella viridis” for the symbiont.

Analysis of the completely determined genomes of the plant-derived Acholeplasma brassicae strain O502 and A. palmae strain J233 revealed that the circular chromosomes are 1,877,792 and 1,554,229 bp in size, have a G + C content of 36 and 29%, and encode 1,690 and 1,439 proteins, respectively. Comparative analysis of these sequences and previously published genomes of A. laidlawii strain PG-8, ‘Candidatus Phytoplasma asteris' strains, ‘Ca. P. australiense' and ‘Ca. P. mali' show a limited shared basic genetic repertoire. The acholeplasma genomes are characterized by a low number of rearrangements, duplication and integration events. Exceptions are the unusual duplication of rRNA operons in A. brassicae and an independently introduced second gene for a single-stranded binding protein in both genera. In contrast to phytoplasmas, the acholeplasma genomes differ by encoding the cell division protein FtsZ, a wide variety of ABC transporters, the F₀F1 ATP synthase, the Rnf-complex, SecG of the Sec-dependent secretion system, a richly equipped repertoire for carbohydrate metabolism, fatty acid, isoprenoid and partial amino acid metabolism. Conserved metabolic proteins encoded in phytoplasma genomes such as the malate dehydrogenase SfcA, several transporters and proteins involved in host-interaction, and virulence-associated effectors were not predicted for the acholeplasmas.

ABSTRACT “ Candidatus Cardinium hertigii” ( Bacteroidetes ) is a maternally inherited endosymbiont known from several arthropods. Its mechanisms for persistence in host populations are mostly reproductive manipulation, though it has been occasionally reported to improve fitness parameters in several hosts. In Culicoides (Diptera: Ceratopogonidae) biting midges, the prevalence of “ Candidatus Cardinium” infection was documented as moderate, with no detectable sex bias. We therefore investigated whether “ Candidatus Cardinium” affects important fitness parameters, such as survival and body size, in Culicoides imicola , a dominant vector species. Field-collected midges were trapped and analyzed for survival under different environmental conditions and antibiotic treatment, taking into account “ Candidatus Cardinium” infection status and parity status (i.e., parous or nulliparous). Additionally, wing lengths were measured as a proxy parameter for body size and analyzed together with “ Candidatus Cardinium” infection data. The findings revealed no difference in survival of Culicoides infected with “ Candidatus Cardinium” and that of uninfected midges in both parity states and under all tested conditions: optimal, starvation, heat, and antibiotic treatment. Beyond survival, no wing length difference was found for “ Candidatus Cardinium”-infected versus uninfected midges. In aggregate, these findings support our conclusion that “ Candidatus Cardinium” does not have an overt effect on the survival and size of adult C. imicola midges. “ Candidatus Cardinium” may affect immature stages or may alter adult reproductive performance.

ABSTRACTHistological analysis of gill samples taken from individuals ofLatris lineatareared in aquaculture in Tasmania, Australia, and those sampled from the wild revealed the presence of epitheliocystis-like basophilic inclusions. Subsequent morphological,in situhybridization, and molecular analyses were performed to confirm the presence of this disease and discovered aChlamydia-like organism associated with this condition, and the criteria set by Fredericks and Relman's postulates were used to establish disease causation. Three distinct 16S rRNA genotypes were sequenced from 16 fish, and phylogenetic analyses of the nearly full-length 16S rRNA sequences generated for this bacterial agent indicated that they were nearly identical novel members of the orderChlamydiales. This new taxon formed a well-supported clade with “CandidatusParilichlamydia carangidicola” from the yellowtail kingfish (Seriola lalandi). On the basis of sequence divergence over the 16S rRNA region relative to all other members of the orderChlamydiales, a new genus and species are proposed here for theChlamydia-like bacterium fromL. lineata, i.e., “CandidatusSimilichlamydia latridicola” gen. nov., sp. nov.