Comparison of metabolic capacities and inference of gene content evolution in mosquito-associated Spiroplasma diminutum and S. taiwanense

Integrated Information for Pathogenicity and Treatment of Spiroplasma

Spiroplasma, belonging to the class Mollicutes, is a small, helical, motile bacterium lacking a cell wall. Its host range includes insects, plants, and aquatic crustaceans. Recently, a few human cases of Spiroplasma infection have been reported. The diseases caused by Spiroplasma have brought about serious economic losses and hindered the healthy development of agriculture. The pathogenesis of Spiroplasma involves the ability to adhere, such as through the terminal structure of Spiroplasma, colonization, and invasive enzymes. However, the exact pathogenic mechanism of Spiroplasma remains a mystery. Therefore, we systematically summarize all the information about Spiroplasma in this review article. This provides a reference for future studies on virulence factors and treatment strategies of Spiroplasma.

The wild solitary bees Andrena vaga, Anthophora plumipes, Colletes cunicularius, and Osmia cornuta microbiota are host specific and dominated by endosymbionts and environmental microorganisms

We characterized the microbial communities of the crop, midgut, hindgut, and ovaries of the wild solitary bees Andrena vaga, Anthophora plumipes, Colletes cunicularius, and Osmia cornuta through 16S rRNA gene and ITS2 amplicon sequencing and a large-scale isolation campaign. The bacterial communities of these bees were dominated by endosymbionts of the genera Wolbachia and Spiroplasma. Bacterial and yeast genera representing the remaining predominant taxa were linked to an environmental origin. While only a single sampling site was examined for Andrena vaga, Anthophora plumipes, and Colletes cunicularius, and two sampling sites for Osmia cornuta, the microbiota appeared to be host specific: bacterial, but not fungal, communities generally differed between the analyzed bee species, gut compartments and ovaries. This may suggest a selective process determined by floral and host traits. Many of the gut symbionts identified in the present study are characterized by metabolic versatility. Whether they exert similar functionalities within the bee gut and thus functional redundancy remains to be elucidated.

Antimicrobial drug resistance mechanisms among Mollicutes

Representatives of the Mollicutes class are the smallest, wall-less bacteria capable of independent reproduction. They are widespread in nature, most are commensals, and some are pathogens of humans, animals and plants. They are also the main contaminants of cell cultures and vaccine preparations. Despite limited biosynthetic capabilities, they are highly adaptable and capable of surviving under various stress and extreme conditions, including antimicrobial selective pressure. This review describes current understanding of antibiotic resistance (ABR) mechanisms in Mollicutes. Protective mechanisms in these bacteria include point mutations, which may include non-target genes, and unique gene exchange mechanisms, contributing to transfer of ABR genes. Better understanding of the mechanisms of emergence and dissemination of ABR in Mollicutes is crucial to control these hypermutable bacteria and prevent the occurrence of highly ABR strains.

The evolution of abdominal microbiomes in fungus-growing ants

The attine ants are a monophyletic lineage that switched to fungus farming ca. 55-60 MYA. They have become a model for the study of complex symbioses after additional fungal and bacterial symbionts were discovered, but their abdominal endosymbiotic bacteria remain largely unknown. Here, we present a comparative microbiome analysis of endosymbiotic bacteria spanning the entire phylogenetic tree. We show that, across 17 representative sympatric species from eight genera sampled in Panama, abdominal microbiomes are dominated by Mollicutes, α- and γ-Proteobacteria, and Actinobacteria. Bacterial abundances increase from basal to crown branches in the phylogeny reflecting a shift towards putative specialized and abundant abdominal microbiota after the ants domesticated gongylidia-bearing cultivars, but before the origin of industrial-scale farming based on leaf-cutting herbivory. This transition coincided with the ancestral single colonization event of Central/North America ca. 20 MYA, documented in a recent phylogenomic study showing that almost the entire crown group of the higher attine ants, including the leaf-cutting ants, evolved there and not in South America. Several bacterial species are located in gut tissues or abdominal organs of the evolutionarily derived, but not the basal attine ants. The composition of abdominal microbiomes appears to be affected by the presence/absence of defensive antibiotic-producing actinobacterial biofilms on the worker ants' cuticle, but the significance of this association remains unclear. The patterns of diversity, abundance and sensitivity of the abdominal microbiomes that we obtained explore novel territory in the comparative analysis of attine fungus farming symbioses and raise new questions for further in-depth research.

Horizontal Gene Acquisitions Contributed to Genome Expansion in Insect-Symbiotic Spiroplasma clarkii

Genome reduction is a recurring theme of symbiont evolution. The genus Spiroplasma contains species that are mostly facultative insect symbionts. The typical genome sizes of those species within the Apis clade were estimated to be ∼1.0–1.4 Mb. Intriguingly, Spiroplasma clarkii was found to have a genome size that is >30% larger than the median of other species within the same clade. To investigate the molecular evolution events that led to the genome expansion of this bacterium, we determined its complete genome sequence and inferred the evolutionary origin of each protein-coding gene based on the phylogenetic distribution of homologs. Among the 1,346 annotated protein-coding genes, 641 were originated from within the Apis clade while 233 were putatively acquired from outside of the clade (including 91 high-confidence candidates). Additionally, 472 were specific to S. clarkii without homologs in the current database (i.e., the origins remained unknown). The acquisition of protein-coding genes, rather than mobile genetic elements, appeared to be a major contributing factor of genome expansion. Notably, >50% of the high-confidence acquired genes are related to carbohydrate transport and metabolism, suggesting that these acquired genes contributed to the expansion of both genome size and metabolic capability. The findings of this work provided an interesting case against the general evolutionary trend observed among symbiotic bacteria and further demonstrated the flexibility of Spiroplasma genomes. For future studies, investigation on the functional integration of these acquired genes, as well as the inference of their contribution to fitness could improve our knowledge of symbiont evolution.

Horizontal Acquisition and Transcriptional Integration of Novel Genes in Mosquito-Associated Spiroplasma

Genetic differentiation among symbiotic bacteria is important in shaping biodiversity. The genus Spiroplasma contains species occupying diverse niches and is a model system for symbiont evolution. Previous studies have established that two mosquito-associated species have diverged extensively in their carbohydrate metabolism genes despite having a close phylogenetic relationship. Notably, although the commensal Spiroplasma diminutum lacks identifiable pathogenicity factors, the pathogenic Spiroplasma taiwanense was found to have acquired a virulence factor glpO and its associated genes through horizontal transfer. However, it is unclear if these acquired genes have been integrated into the regulatory network. In this study, we inferred the gene content evolution in these bacteria, as well as examined their transcriptomes in response to glucose availability. The results indicated that both species have many more gene acquisitions from the Mycoides-Entomoplasmataceae clade, which contains several important pathogens of ruminants, than previously thought. Moreover, several acquired genes have higher expression levels than the vertically inherited homologs, indicating possible functional replacement. Finally, the virulence factor and its functionally linked genes in S. taiwanense were up-regulated in response to glucose starvation, suggesting that these acquired genes are under expression regulation and the pathogenicity may be a stress response. In summary, although differential gene losses are a major process for symbiont divergence, gene gains are critical in counteracting genome degradation and driving diversification among facultative symbionts.

Complete Genome Sequence of Spiroplasma monobiae MQ-1T (ATCC 33825), a Bacterium Isolated from the Vespid Wasp (Monobia quadridens)

Spiroplasma monobiae MQ-1T (ATCC 33825) was isolated from the hemolymph of an adult vespid wasp (Monobia quadridens) collected in Maryland. Here, we report the complete genome sequence of this bacterium to facilitate the investigation of its biology and the comparative genomics among Spiroplasma species.

Hydrogen peroxide production and myo-inositol metabolism as important traits for virulence of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae is the causative agent of enzootic pneumonia. In our previous work, we reconstructed the metabolic models of this species along with two other mycoplasmas from the respiratory tract of swine: Mycoplasma hyorhinis, considered less pathogenic but which nonetheless causes disease and Mycoplasma flocculare, a commensal bacterium. We identified metabolic differences that partially explained their different levels of pathogenicity. One important trait was the production of hydrogen peroxide from the glycerol metabolism only in the pathogenic species. Another important feature was a pathway for the metabolism of myo-inositol in M. hyopneumoniae. Here, we tested these traits to understand their relation to the different levels of pathogenicity, comparing not only the species but also pathogenic and attenuated strains of M. hyopneumoniae. Regarding the myo-inositol metabolism, we show that only M. hyopneumoniae assimilated this carbohydrate and remained viable when myo-inositol was the primary energy source. Strikingly, only the two pathogenic strains of M. hyopneumoniae produced hydrogen peroxide in complex medium. We also show that this production was dependent on the presence of glycerol. Although further functional tests are needed, we present in this work two interesting metabolic traits of M. hyopneumoniae that might be directly related to its enhanced virulence.

Complete Genome Sequence of Spiroplasma floricola 23-6 T (ATCC 29989), a Bacterium Isolated from a Tulip Tree (Liriodendron tulipifera L.)

Spiroplasma floricola 23-6^T (ATCC 29989) was isolated from the flower surface of a tulip tree (Liriodendron tulipifera L.). Here, we report the complete genome sequence of this bacterium to facilitate the investigation of its biology and the comparative genomics among Spiroplasma species.

Draft Genome Sequence of Burkholderia sp. Strain WAC0059, a Bacterium Isolated from the Medicinal Fungus Antrodia cinnamomea

Burkholderia sp. strain WAC0059 was isolated from a fruiting body of the medicinal fungus Antrodia cinnamomea collected in Taiwan. Here, we report the draft genome sequence of this bacterium to facilitate the investigation of its biology.

Winding paths to simplicity: genome evolution in facultative insect symbionts

Symbiosis between organisms is an important driving force in evolution. Among the diverse relationships described, extensive progress has been made in insect–bacteria symbiosis, which improved our understanding of the genome evolution in host-associated bacteria. Particularly, investigations on several obligate mutualists have pushed the limits of what we know about the minimal genomes for sustaining cellular life. To bridge the gap between those obligate symbionts with extremely reduced genomes and their non-host-restricted ancestors, this review focuses on the recent progress in genome characterization of facultative insect symbionts. Notable cases representing various types and stages of host associations, including those from multiple genera in the family Enterobacteriaceae (class Gammaproteobacteria), Wolbachia (Alphaproteobacteria) and Spiroplasma (Mollicutes), are discussed. Although several general patterns of genome reduction associated with the adoption of symbiotic relationships could be identified, extensive variation was found among these facultative symbionts. These findings are incorporated into the established conceptual frameworks to develop a more detailed evolutionary model for the discussion of possible trajectories. In summary, transitions from facultative to obligate symbiosis do not appear to be a universal one-way street; switches between hosts and lifestyles (e.g. commensalism, parasitism or mutualism) occur frequently and could be facilitated by horizontal gene transfer.

This review synthesizes the recent progress in genome characterization of insect-symbiotic bacteria, the emphases include (i) patterns of genome organization, (ii) evolutionary models and trajectories, and (iii) comparisons between facultative and obligate symbionts.

Glycerol metabolism and its implication in virulence in Mycoplasma

Glycerol and glycerol-containing compounds such as lipids belong to the most abundant organic compounds that may serve as nutrient for many bacteria. For the cell wall-less bacteria of the genus Mycoplasma, glycerol derived from phospholipids of their human or animal hosts is the major source of carbon and energy. The lipids are first degraded by lipases, and the resulting glycerophosphodiesters are transported into the cell and cleaved to release glycerol-3-phosphate. Alternatively, free glycerol can be transported, and then become phosphorylated. The oxidation of glycerol-3-phosphate in Mycoplasma spp. as well as in related firmicutes involves a hydrogen peroxide-generating glycerol-3-phosphate oxidase. This enzyme is a key player in the virulence of Mycoplasma spp. as the produced hydrogen peroxide is one of the major virulence factors of these bacteria. In this review, the different components involved in the utilization of lipids and glycerol in Mycoplasma pneumoniae and related bacteria are discussed.

Complete Genome Sequence of Spiroplasma corruscae EC-1 T (DSM 19793), a Bacterium Isolated from a Lampyrid Beetle (Ellychnia corrusca)

Spiroplasma corruscae EC-1^T (DSM 19793) was isolated from the gut of a lampryid beetle (Ellychnia corrusca) collected in Beltsville, MD, USA, in 1983. Here, we report the complete genome sequence of this bacterium to facilitate the investigation of its biology and the comparative genomics among Spiroplasma species.

Complete Genome Sequence of Spiroplasma sp. TU-14

Spiroplasma sp. TU-14 was isolated from a contaminated sample of Entomoplasma lucivorax PIPN-2^T obtained from the International Organization for Mycoplasmology collection. Here, we report the complete genome sequence of this bacterium to facilitate the investigation of its biology and the comparative genomics among Spiroplasma spp.

Complete Genome Sequence of Spiroplasma turonicum Tab4c T , a Bacterium Isolated from Horse Flies ( Haematopota sp.)

Spiroplasma turonicum Tab4c^T was isolated from a horse fly (Haematopota sp.; probably Haematopota pluvialis) collected at Champchevrier, Indre-et-Loire, Touraine, France, in 1991. Here, we report the complete genome sequence of this bacterium to facilitate the investigation of its biology and the comparative genomics among Spiroplasma spp.

Complete Genome Sequence of Spiroplasma helicoides TABS-2T (DSM 22551), a Bacterium Isolated from a Horsefly (Tabanus abactor)

Spiroplasma helicoides TABS-2^T (DSM 22551) was isolated from the gut of a horsefly (Tabanus abactor) collected near Ardmore, Oklahoma, USA, in 1987. Here, we report the complete genome sequence of this bacterium to facilitate the investigation of its biology and the comparative genomics among Spiroplasma species.

Complete Genome Sequence of Spiroplasma cantharicola CC-1 T (DSM 21588), a Bacterium Isolated from Soldier Beetle ( Cantharis carolinus )

Spiroplasma cantharicola CC-1^T (DSM 21588) was isolated from the gut of a soldier beetle (Cantharis carolinus) collected in Maryland, USA. Here, we report the complete genome sequence of this bacterium to facilitate the investigation of its biology.

Genome Analysis of Pseudomonas fluorescens PCL1751: A Rhizobacterium that Controls Root Diseases and Alleviates Salt Stress for Its Plant Host

Pseudomonas fluorescens PCL1751 is a rod-shaped Gram-negative bacterium isolated from the rhizosphere of a greenhouse-grown tomato plant in Uzbekistan. It controls several plant root diseases caused by Fusarium fungi through the mechanism of competition for nutrients and niches (CNN). This mechanism does not rely on the production of antibiotics, so it avoids the concerns of resistance development and is environmentally safe. Additionally, this bacterium promotes plant growth by alleviating salt stress for its plant host. To investigate the genetic mechanisms that may explain these observations, we determined the complete genome sequence of this bacterium, examined its gene content, and performed comparative genomics analysis with other Pseudomonas strains. The genome of P. fluorescens PCL1751 consisted of one circular chromosome that is 6,143,950 base-pairs (bp) in size; no plasmid was found. The annotation included 19 rRNA, 70 tRNA, and 5,534 protein-coding genes. The gene content analysis identified a large number of genes involved in chemotaxis and motility, colonization of the rhizosphere, siderophore biosynthesis, and osmoprotectant production. In contrast, the pathways involved in the biosynthesis of phytohormones or antibiotics were not found. Comparison with other Pseudomonas genomes revealed extensive variations in their genome size and gene content. The presence and absence of secretion system genes were highly variable. As expected, the synteny conservation among strains decreased as a function of phylogenetic divergence. The integration of prophages appeared to be an important driver for genome rearrangements. The whole-genome gene content analysis of this plant growth-promoting rhizobacterium (PGPR) provided some genetic explanations to its phenotypic characteristics. The extensive and versatile substrate utilization pathways, together with the presence of many genes involved in competitive root colonization, provided further support for the finding that this strain achieves biological control of pathogens through effective competition for nutrients and niches.

Complete Genome Sequence of Spiroplasma litorale TN-1T (DSM 21781), a Bacterium Isolated from a Green-Eyed Horsefly (Tabanus nigrovittatus)

Spiroplasma litorale TN-1^T (DSM 21781) was isolated from the gut of a green-eyed horsefly (Tabanus nigrovittatus), collected at Ocracoke Island in North Carolina in 1983. Here, we report the complete genome sequence of this bacterium to facilitate the investigation of its biology.

Found and Lost: The Fates of Horizontally Acquired Genes in Arthropod-Symbiotic Spiroplasma

Horizontal gene transfer (HGT) is an important mechanism that contributed to biological diversity, particularly in bacteria. Through acquisition of novel genes, the recipient cell may change its ecological preference and the process could promote speciation. In this study, we determined the complete genome sequence of two Spiroplasma species for comparative analyses and inferred the putative gene gains and losses. Although most Spiroplasma species are symbionts of terrestrial insects, Spiroplasma eriocheiris has evolved to be a lethal pathogen of freshwater crustaceans. We found that approximately 7% of the genes in this genome may have originated from HGT and these genes expanded the metabolic capacity of this organism. Through comparison with the closely related Spiroplasma atrichopogonis, as well as other more divergent lineages, our results indicated that these HGT events could be traced back to the most recent common ancestor of these two species. However, most of these horizontally acquired genes have been pseudogenized in S. atrichopogonis, suggesting that they did not contribute to the fitness of this lineage that maintained the association with terrestrial insects. Thus, accumulation of small deletions that disrupted these foreign genes was not countered by natural selection. On the other hand, the long-term survival of these horizontally acquired genes in the S. eriocheiris genome hinted that they might play a role in the ecological shift of this species. Finally, the implications of these findings and the conflicts among gene content, 16S rRNA gene sequencing, and serological typing, are discussed in light of defining bacterial species.

Complete Genome Sequence of Agrobacterium tumefaciens Ach5

Agrobacterium tumefaciens is a phytopathogenic bacterium that causes crown gall disease. The strain Ach5 was isolated from yarrow (Achillea ptarmica L.) and is the wild-type progenitor of other derived strains widely used for plant transformation. Here, we report the complete genome sequence of this bacterium.

Genome sequence of the Drosophila melanogaster male-killing Spiroplasma strain MSRO endosymbiont

Spiroplasmas are helical and motile members of a cell wall-less eubacterial group called Mollicutes. Although all spiroplasmas are associated with arthropods, they exhibit great diversity with respect to both their modes of transmission and their effects on their hosts; ranging from horizontally transmitted pathogens and commensals to endosymbionts that are transmitted transovarially (i.e., from mother to offspring). Here we provide the first genome sequence, along with proteomic validation, of an endosymbiotic inherited Spiroplasma bacterium, the Spiroplasma poulsonii MSRO strain harbored by Drosophila melanogaster. Comparison of the genome content of S. poulsonii with that of horizontally transmitted spiroplasmas indicates that S. poulsonii has lost many metabolic pathways and transporters, demonstrating a high level of interdependence with its insect host. Consistent with genome analysis, experimental studies showed that S. poulsonii metabolizes glucose but not trehalose. Notably, trehalose is more abundant than glucose in Drosophila hemolymph, and the inability to metabolize trehalose may prevent S. poulsonii from overproliferating. Our study identifies putative virulence genes, notably, those for a chitinase, the H₂O₂-producing glycerol-3-phosphate oxidase, and enzymes involved in the synthesis of the eukaryote-toxic lipid cardiolipin. S. poulsonii also expresses on the cell membrane one functional adhesion-related protein and two divergent spiralin proteins that have been implicated in insect cell invasion in other spiroplasmas. These lipoproteins may be involved in the colonization of the Drosophila germ line, ensuring S. poulsonii vertical transmission. The S. poulsonii genome is a valuable resource to explore the mechanisms of male killing and symbiont-mediated protection, two cardinal features of many facultative endosymbionts.

Most insect species, including important disease vectors and crop pests, harbor vertically transmitted endosymbiotic bacteria. These endosymbionts play key roles in their hosts’ fitness, including protecting them against natural enemies and manipulating their reproduction in ways that increase the frequency of symbiont infection. Little is known about the molecular mechanisms that underlie these processes. Here, we provide the first genome draft of a vertically transmitted male-killing Spiroplasma bacterium, the S. poulsonii MSRO strain harbored by D. melanogaster. Analysis of the S. poulsonii genome was complemented by proteomics and ex vivo metabolic experiments. Our results indicate that S. poulsonii has reduced metabolic capabilities and expresses divergent membrane lipoproteins and potential virulence factors that likely participate in Spiroplasma-host interactions. This work fills a gap in our knowledge of insect endosymbionts and provides tools with which to decipher the interaction between Spiroplasma bacteria and their well-characterized host D. melanogaster, which is emerging as a model of endosymbiosis.

Draft Genome Sequences of Two Strains of Serratia spp. from the Midgut of the Malaria Mosquito Anopheles gambiae

Here, we report the annotated draft genome sequences of two strains of Serratia spp., Ag1 and Ag2, isolated from the midgut of two different strains of Anopheles gambiae. The genomes of these two strains are almost identical.

Complete Genome Sequence of "Candidatus Sulcia muelleri" ML, an Obligate Nutritional Symbiont of Maize Leafhopper (Dalbulus maidis)

“Candidatus Sulcia muelleri” is a symbiont of sap-feeding insects in the suborder Auchenorrhyncha. The strain “Ca. Sulcia muelleri” ML is associated with the maize leafhopper (Dalbulus maidis), collected in Brazil, which is a disease vector that affects corn production. Here, we report the complete genome sequence of this bacterium.

Arthropod-Spiroplasma relationship in the genomic era

The genus Spiroplasma comprises wall-less, low-GC bacteria that establish pathogenic, mutualistic and commensal symbiotic associations with arthropods and plants. This review focuses on the symbiotic relationships between Spiroplasma bacteria and arthropod hosts in the context of the available genomic sequences. Spiroplasma genomes are reduced and some contain highly repetitive plectrovirus-related sequences. Spiroplasma's diversity in viral invasion susceptibility, virulence factors, substrate utilization, genome dynamics and symbiotic associations with arthropods make this bacterial genus a biological model that provides insights about the evolutionary traits that shape bacterial symbiotic relationships with eukaryotes.

Molecular evolution of the substrate utilization strategies and putative virulence factors in mosquito-associated Spiroplasma species

Comparative genomics provides a powerful tool to characterize the genetic differences among species that may be linked to their phenotypic variations. In the case of mosquito-associated Spiroplasma species, such approach is useful for the investigation of their differentiations in substrate utilization strategies and putative virulence factors. Among the four species that have been assessed for pathogenicity by artificial infection experiments, Spiroplasma culicicola and S. taiwanense were found to be pathogenic, whereas S. diminutum and S. sabaudiense were not. Intriguingly, based on the species phylogeny, the association with mosquito hosts and the gain or loss of pathogenicity in these species appears to have evolved independently. Through comparison of their complete genome sequences, we identified the genes and pathways that are shared by all or specific to one of these four species. Notably, we found that a glycerol-3-phosphate oxidase gene (glpO) is present in S. culicicola and S. taiwanense but not in S. diminutum or S. sabaudiense. Because this gene is involved in the production of reactive oxygen species and has been demonstrated as a major virulence factor in Mycoplasma, this distribution pattern suggests that it may be linked to the observed differences in pathogenicity among these species as well. Moreover, through comparative analysis with other Spiroplasma, Mycoplasma, and Mesoplasma species, we found that the absence of glpO in S. diminutum and S. sabaudiense is best explained by independent losses. Finally, our phylogenetic analyses revealed possible recombination of glpO between distantly related lineages and local rearrangements of adjacent genes.

Complete Genome Sequence of Vibrio vulnificus 93U204, a Bacterium Isolated from Diseased Tilapia in Taiwan

Vibrio vulnificus 93U204 is a bacterium isolated from a moribund tilapia collected in Kaohsiung, Taiwan. Here, we report the complete genome sequence of this bacterium to facilitate the investigation of its pathogenicity and for comparative analyses with human-pathogenic strains within the same species.

Hydrogen peroxide production from glycerol metabolism is dispensable for virulence of Mycoplasma gallisepticum in the tracheas of chickens

Hydrogen peroxide (H2O2) is a by-product of glycerol metabolism in mycoplasmas and has been shown to cause cytotoxicity for cocultured eukaryotic cells. There appears to be selective pressure for mycoplasmas to retain the genes needed for glycerol metabolism. This has generated interest and speculation as to their function during infection. However, the actual effects of glycerol metabolism and H2O2 production on virulence in vivo have never been assessed in any Mycoplasma species. To this end, we determined that the wild-type (WT) R(low) strain of the avian pathogen Mycoplasma gallisepticum is capable of producing H2O2 when grown in glycerol and is cytotoxic to eukaryotic cells in culture. Transposon mutants with mutations in the genes present in the glycerol transport and utilization pathway, namely, glpO, glpK, and glpF, were identified. All mutants assessed were incapable of producing H2O2 and were not cytotoxic when grown in glycerol. We also determined that vaccine strains ts-11 and 6/85 produce little to no H2O2 when grown in glycerol, while the naturally attenuated F strain does produce H2O2. Chickens were infected with one of two glpO mutants, a glpK mutant, R(low), or growth medium, and tracheal mucosal thickness and lesion scores were assessed. Interestingly, all glp mutants were reproducibly virulent in the respiratory tracts of the chickens. Thus, there appears to be no link between glycerol metabolism/H2O2 production/cytotoxicity and virulence for this Mycoplasma species in its natural host. However, it is possible that glycerol metabolism is required by M. gallisepticum in a niche that we have yet to study.

Invasion of insect cells by Spiroplasma citri involves spiralin relocalization and lectin/glycoconjugate-type interactions

Spiroplamas are helical, cell wall-less bacteria belonging to the Class Mollicutes, a group of microorganisms phylogenetically related to low G+C, Gram-positive bacteria. Spiroplasma species are all found associated with arthropods and a few, including Spiroplasma citri are pathogenic to plant. Thus S. citri has the ability to colonize cells of two very distinct hosts, the plant and the insect vector. While spiroplasmal factors involved in transmission by the leafhopper Circulifer haematoceps have been identified, their specific contribution to invasion of insect cells is poorly understood. In this study we provide evidence that the lipoprotein spiralin plays a major role in the very early step of cell invasion. Confocal laser scanning immunomicroscopy revealed a relocalization of spiralin at the contact zone of adhering spiroplasmas. The implication of a role for spiralin in adhesion to insect cells was further supported by adhesion assays showing that a spiralin-less mutant was impaired in adhesion and that recombinant spiralin triggered adhesion of latex beads. We also showed that cytochalasin D induced changes in the surface-exposed glycoconjugates, as inferred from the lectin binding patterns, and specifically improved adhesion of S. citri wild-type but not of the spiralin-less mutant. These results indicate that cytochalasin D exposes insect cell receptors of spiralin that are masked in untreated cells. In addition, competitive adhesion assays with lectins strongly suggest spiralin to exhibit glycoconjugate binding properties similar to that of the Vicia villosa agglutinin (VVA) lectin.

Complete Genome Sequence of Spiroplasma apis B31T (ATCC 33834), a Bacterium Associated with May Disease of Honeybees (Apis mellifera)

Spiroplasma apis B31^T (ATCC 33834) is a wall-less bacterium in the class Mollicutes that has been linked to May disease of honeybees (Apis mellifera). Here, we report the complete genome sequence of this bacterium to facilitate the investigation of its virulence factors.