Microbiology

Phytoplasmas classified in group 16SrXII infect a wide range of plants and are transmitted by polyphagous planthoppers of the family Cixiidae. Based on 16S rRNA gene sequence identity and biological properties, group 16SrXII encompasses several species, including ‘CandidatusPhytoplasma australiense’, ‘CandidatusPhytoplasma japonicum’ and ‘CandidatusPhytoplasma fragariae’. Other group 16SrXII phytoplasma strains are associated with stolbur disease in wild and cultivated herbaceous and woody plants and with bois noir disease in grapevines (Vitis viniferaL.). Such latter strains have been informally proposed to represent a separate species, ‘CandidatusPhytoplasma solani’, but a formal description of this taxon has not previously been published. In the present work, stolbur disease strain STOL11 (STOL) was distinguished from reference strains of previously described species of the ‘CandidatusPhytoplasma’ genus based on 16S rRNA gene sequence similarity and a unique signature sequence in the 16S rRNA gene. Other stolbur- and bois noir-associated (‘Ca.Phytoplasma solani’) strains shared >99 % 16S rRNA gene sequence similarity with strain STOL11 and contained the signature sequence. ‘Ca.Phytoplasma solani’ is the only phytoplasma known to be transmitted byHyalesthes obsoletus. Insect vectorship and molecular characteristics are consistent with the concept that diverse ‘Ca.Phytoplasma solani’ strains share common properties and represent an ecologically distinct gene pool. Phylogenetic analyses of 16S rRNA,tuf,secYandrplV–rpsCgene sequences supported this view and yielded congruent trees in which ‘Ca.Phytoplasma solani’ strains formed, within the group 16SrXII clade, a monophyletic subclade that was most closely related to, but distinct from, that of ‘Ca.Phytoplasma australiense’-related strains. Based on distinct molecular and biological properties, stolbur- and bois noir-associated strains are proposed to represent a novel species level taxon, ‘Ca.Phytoplasma solani’; STOL11 is designated the reference strain.

Summary Knowledge 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 A delges tsugae , a pest of hemlocks in eastern N orth A merica introduced from A sia. Amplification, cloning, and sequencing of bacterial 16 S rDNA , in situ hybridizations, and electron microscopy revealed that A . tsugae harbours up to five bacterial phylotypes, according to population. Three G ammaproteobacteria species are maternally transmitted. The first, designated ‘ C a . P seudomonas adelgestsugas’ resides in the haemocoel, and was detected in all populations except T aiwan. The second phylotype, ‘ C a . S erratia symbiotica’, resides in bacteriocytes of populations on T suga sieboldii in J apan and in E . N orth A merica. The third phylotype, designated ‘ C a . A nnandia adelgestsuga’, clustered within a lineage of several insect endosymbionts that included B uchnera aphidicola . It was detected in bacteriocytes in all populations, and in salivary glands of first instars. Two B etaproteobacteria phylotypes were detected in some J apanese T . sieboldii and eastern N orth A merica 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.

Summary Many hemipterans are associated with symbiotic bacteria, which are usually found intracellularly in specific bacteriomes. In this study, we provide the first molecular identification of the bacteriome‐associated, obligate endosymbiont in a G ondwanan relict insect taxon, the moss bugs ( H emiptera: C oleorrhyncha: P eloridiidae), which represents one of the oldest lineages within the H emiptera. Endosymbiotic associations of fifteen species of the family were analysed, covering representatives from S outh A merica, A ustralia/ T asmania and N ew Z ealand. Phylogenetic analysis based on four kilobases of 16 S –23 S r RNA gene fragments showed that the obligate endosymbiont of P eloridiidae constitute a so far unknown group of G ammaproteobacteria which is named here ‘ Candidatus Evansia muelleri’. They are related to the sternorrhynchous endosymbionts C andidatus   P ortiera and C andidatus   C arsonella. Comparison of the primary‐endosymbiont and host ( COI  + 28 S rRNA ) trees showed overall congruence indicating co‐speciation the hosts and their symbionts. The distribution of the endosymbiont within the insect body and its transmission was studied using FISH . The endosymbionts were detected endocellularly in a pair of bacteriomes as well as in the ‘symbiont ball’ of the posterior pole of each developing oocyte. Furthermore, ultrastructural analysis of the M alpighian tubules revealed that most host nuclei are infected by an endosymbiotic, intranuclear bacterium that was determined as an A lphaproteobacterium of the genus R ickettsia .

Abstract ‘Candidatus Microthrix parvicella’ is a lipid-accumulating, filamentous bacterium so far found only in activated sludge wastewater treatment plants, where it is a common causative agent of sludge separation problems. Despite attracting considerable interest, its detailed physiology is still unclear. In this study, the genome of the RN1 strain was sequenced and annotated, which facilitated the construction of a theoretical metabolic model based on available in situ and axenic experimental data. This model proposes that under anaerobic conditions, this organism accumulates preferentially long-chain fatty acids as triacylglycerols. Utilisation of trehalose and/or polyphosphate stores or partial oxidation of long-chain fatty acids may supply the energy required for anaerobic lipid uptake and storage. Comparing the genome sequence of this isolate with metagenomes from two full-scale wastewater treatment plants with enhanced biological phosphorus removal reveals high similarity, with few metabolic differences between the axenic and the dominant community ‘Ca. M. parvicella’ strains. Hence, the metabolic model presented in this paper could be considered generally applicable to strains in full-scale treatment systems. The genomic information obtained here will provide the basis for future research into in situ gene expression and regulation. Such information will give substantial insight into the ecophysiology of this unusual and biotechnologically important filamentous bacterium.

This work characterizes a unicellular cyanobacterium with nearly spherical cells and thin-outlined sheaths that divide irregularly, forming small packets immersed in a diffluent mucilaginous layer. It was isolated growing on calcite speleothems and walls in a show cave in Collbató (Barcelona, Spain). Spectral confocal laser and transmission electron microscopy were used to describe the morphology, fine structure and thylakoid arrangement. The pigments identified were phycoerythrin, phycocyanin, allophycocyanin and chlorophyll a. Three-dimensional reconstructions, generated from natural fluorescence z-stacks, revealed a large surface area of nearly flat, arm-like thylakoidal membranes connected to each other and forming a unified structure in a way that, to our knowledge, has never been described before. Phylogenetic analyses using the 16S rRNA gene sequence showed 95 % similarity to strain Chroococcus sp. JJCM (GenBank accession no. AM710384). The diacritical phenotypic features do not correspond to any species currently described, and the genetic traits support the strain being classified as the first member of an independent genus in the order Chroococcales and the family Chroococcaceae. Hence, we propose the name Chalicogloea cavernicola gen. nov., sp. nov. under the provisions of the International Code of Nomenclature for Algae, Fungi and Plants. The type strain of Chalicogloea cavernicola is COLL 3T ( = CCALA 975T  = CCAP 1424/1T).