Publications

3868

Symbiotic microbes from the genus 'Candidatus Megaira' ( Rickettsiales ) are known to be common associates of algae and ciliates. However, genomic resources for these bacteria are scarce, limiting our understanding of their diversity and biology. We therefore utilize Sequence Read Archive and metagenomic assemblies to explore the diversity of this genus. We successfully extract four draft 'Ca. Megaira' genomes including one complete scaffold for a 'Ca. Megaira' and identify an additional 14 draft genomes from uncategorized environmental metagenome-assembled genomes. We use this information to resolve the phylogeny for the hyper-diverse 'Ca. Megaira', with hosts broadly spanning ciliates, and micro- and macro-algae, and find that the current single genus designation 'Ca. Megaira' significantly underestimates their diversity. We also evaluate the metabolic potential and diversity of ''Ca. Megaira' from this new genomic data and find no clear evidence of nutritional symbiosis. In contrast, we hypothesize a potential for defensive symbiosis in 'Ca. Megaira'. Intriguingly, one symbiont genome revealed a proliferation of ORFs with ankyrin, tetratricopeptide and leucine-rich repeats such as those observed in the genus Wolbachia where they are considered important for host–symbiont protein–protein interactions. Onward research should investigate the phenotypic interactions between 'Ca. Megaira' and their various potential hosts, including the economically important Nemacystus decipiens, and target acquisition of genomic information to reflect the diversity of this massively variable group.

Pentastiridius leporinus is a planthopper (Hemiptera: Cixiidae) that vectors two phloem-restricted bacterial pathogens to sugar beet (Beta vulgaris (L.)): the γ-proteobacterium Candidatus Arsenophonus phytopathogenicus and the stolbur phytoplasma Candidatus Phytoplasma solani. These bacteria cause an economically important disease known as syndrome basses richesses (SBR), characterized by yellowing, deformed leaves and low beet yields. Having observed potato fields in Germany infested with cixiid planthoppers and showing signs of leaf yellowing, we used morphological criteria and COI and COII as molecular markers, to identify the planthoppers (adults and nymphs) primarily as P. leporinus. We analyzed planthoppers, potato tubers, and sugar beet roots and detected both pathogens in all sample types, confirming that P. leporinus adults and nymphs can transmit the bacteria. This is the first time that P. leporinus has been shown to transmit Arsenophonus to potato plants. We also found that two generations of P. leporinus were produced in the warm summer of 2022, which will probably increase the pest population size (and thus the prevalence of SBR) in 2023. We conclude that P. leporinus has expanded its host range to potato, and can now utilize both host plants during its developmental cycle, a finding that will facilitate the development of more efficient control strategies.

Spotted fever illness caused by the tick-borne pathogen Rickettsia parkeri has emerged in the Pampa biome in southern Brazil, where the tick Amblyomma tigrinum is implicated as the main vector. Because domestic dogs are commonly parasitized by A. tigrinum, this canid is also a suitable sentinel for R. parkeri-associated spotted fever. Herein, we investigate rickettsial infection in ticks, domestic dogs and small mammals in a natural reserve of the Pampa biome in southern Brazil. The ticks A. tigrinum, Amblyomma aureolatum and Rhipicephalus sanguineus were collected from dogs. Molecular analyses of ticks did not detect R. parkeri; however, at least 34% (21/61) of the A. tigrinum ticks were infected by the non-pathogenic agent ‘Candidatus Rickettsia andeanae’. Serological analyses revealed that only 14% and 3% of 36 dogs and 34 small mammals, respectively, were exposed to rickettsial antigens. These results indicate that the study area is not endemic for R. parkeri rickettsiosis. We tabulated 10 studies that reported rickettsial infection in A. tigrinum populations from South America. There was a strong negative correlation between the infection rates by R. parkeri and ‘Candidatus R. andeanae’ in A. tigrinum populations. We propose that high infection rates by ‘Candidatus R. andeanae’ might promote the exclusion of R. parkeri from A. tigrinum populations. The mechanisms for such exclusion are yet to be elucidated.

AbstractMarine bacterial lineages associated with algal blooms, such as the Roseobacter clade, have been well characterized in ecological and genomic contexts, yet such lineages have rarely been explored in freshwater blooms. This study performed phenotypic and genomic analyses of an alphaproteobacterial lineage ‘Candidatus Phycosocius’ (denoted the CaP clade), one of the few lineages ubiquitously associated with freshwater algal blooms, and described a novel species: ‘Ca. Phycosocius spiralis.’ Phylogenomic analyses indicated that the CaP clade is a deeply branching lineage in the Caulobacterales. Pangenome analyses revealed characteristic features of the CaP clade: aerobic anoxygenic photosynthesis and essential vitamin B auxotrophy. Genome size varies widely among members of the CaP clade (2.5–3.7 Mb), likely a result of independent genome reductions at each lineage. This includes a loss of tight adherence pilus genes (tad) in ‘Ca. P. spiralis’ that may reflect its adoption of a unique spiral cell shape and corkscrew-like burrowing activity at the algal surface. Notably, quorum sensing (QS) proteins showed incongruent phylogenies, suggesting that horizontal transfers of QS genes and QS-involved interactions with specific algal partners might drive CaP clade diversification. This study elucidates the ecophysiology and evolution of proteobacteria associated with freshwater algal blooms.

Abstract Thi.o.ha.lo.rhab.da.ce'ae N.L. fem. n. Thiohalorhabdus , the type genus of the family; L. fem. pl. n. suff.‐ aceae , ending to denote a family; N.L. fem. pl. n. Thiohalorhabdaceae , the Thiohalorhabdus family. Proteobacteria / Gammaproteobacteria / Thiohalorhabdales / Thiohalorhabdaceae fam. nov. The family Thiohalorhabdaceae incorporates facultatively anaerobic, chemolithoautotrophic, sulfur‐oxidizing bacteria from hypersaline habitats. They are extreme halophiles utilizing reduced sulfur compounds as energy sources with either O 2 or nitrate as the electron acceptor and assimilating CO 2 via the Calvin–Benson–Bassham cycle. The family is a member of the order Thiohalorhabdales in the Gammaproteobacteria, and it consists of a single genus Thiohalorhabdus . The family‐level status was established by phylogenomic analysis based on the Genome Taxonomy DataBase classification. DNA G  +  C content (%) : 68.9 (genome of the type strain). Type genus : Thiohalorhabdus Sorokin et al. 2008 VP .

Abstract Thi.o.ha.lo.rhab.dal'es N.L. fem. n. Thiohalorhabdus , the type genus of the order; L. fem. pl. n. suff. ‐ ales ending to denote an order; N.L. fem. pl. n. Thiohalorhabdales , order of the genus Thiohalorhabdus . Proteobacteria / Gammaproteobacteria / Thiohalorhabdales ord. nov. According to the phylogenomic analysis, the order Thiohalorhabdales forms a deeply branching phylogenetic lineage at the base of the Gammaproteobacteria . It consists of a single family Thiohalorhabdaceae and genus Thiohalorhabdus . The cultured members of the order are extremely halophilic, facultatively anaerobic (denitrifying), chemolithoautotrophic, sulfur‐oxidizing bacteria from hypersaline habitats with neutral pH. Type genus : Thiohalorhabdus Sorokin et al. 2008 VP .

Abstract Thi.o.ha.lo.bac.ter.al'es N.L. masc. n. Thiohalobacter , the type genus of the order; L. fem. pl. n. suff. ‐ ales , ending to denote an order; N.L. fem. pl. n. Thiohalobacterales , the order of the genus Thiohalobacter . Proteobacteria / Gammaproteobacteria / Thiohalobacterales ord. nov. The order Thiohalobacterales accommodates obligately chemolithoautotrophic aerobic bacteria utilizing inorganic sulfur compounds as the energy source and assimilating CO 2 via the Calvin–Benson–Bassham cycle. The order is a deeply branching member of the Gammaproteobacteria and consists of two families Thiohalobacteraceae and Thiogranaceae, both of which include one genus. The order‐level status was established by phylogenomic analysis based on the Genome Taxonomy DataBase classification. Type genus : Thiohalobacter Sorokin et al. 2010 VP .

Abstract Thi.o.ha.lo.bac.ter.a.ce'ae N.L. masc. n. Thiohalobacter , the type genus of the family, ‐ aceae ending to denote a family; N.L. fem. pl. n. Thiohalobacteraceae the Thiohalobacter family. Proteobacteria / Gammaproteobacteria / Thiohalobacterales / Thiohalobacteraceae fam. nov. The family Thiohalobacteraceae consists of aerobic, chemolithoautotrophic, sulfur‐oxidizing bacteria from hypersaline salt lakes. They are moderately halophilic aerobic, bacteria utilizing reduced sulfur compounds as the energy source and assimilating CO 2 via the Calvin–Benson–Bassham cycle. The family is a member of the order Thiohalobacterales within the Gammaproteobacteria and consists of a single genus Thiohalobacter . The family‐level status was established by phylogenomic analysis based on the Genome Taxonomy DataBase classification. DNA G + C content (%) : 64.2 (genome sequence). Type genus : Thiohalobacter Sorokin et al. 2010 VP .

AbstractThe order Holosporales (Alphaproteobacteria) encompasses obligate intracellular bacterial symbionts of diverse Eukaryotes. These bacteria have highly streamlined genomes and can have negative fitness effects on the host. Herein, we present a comparative analysis of the first genome sequences of ‘Ca. Hepatincola porcellionum’, a facultative symbiont occurring extracellularly in the midgut glands of terrestrial isopods. Using a combination of long-read and short-read sequencing, we obtained the complete circular genomes of two Hepatincola strains and an additional metagenome-assembled draft genome. Phylogenomic analysis validated its phylogenetic position as an early-branching family-level clade relative to all other established Holosporales families associated with protists. A 16S rRNA gene survey revealed that this new family encompasses diverse bacteria associated with both marine and terrestrial host species, which expands the host range of Holosporales bacteria from protists to several phyla of the Ecdysozoa (Arthropoda and Priapulida). Hepatincola has a highly streamlined genome with reduced metabolic and biosynthetic capacities as well as a large repertoire of transmembrane transporters. This suggests that this symbiont is rather a nutrient scavenger than a nutrient provider for the host, likely benefitting from a nutrient-rich environment to import all necessary metabolites and precursors. Hepatincola further possesses a different set of bacterial secretion systems compared to protist-associated Holosporales, suggesting different host-symbiont interactions depending on the host organism.

Abstract Understanding vector dispersal capacity is key to assessing the risk of spread of vector borne pathogens. For flying vectors, flight performance is associated with primary and secondary pathogen spread. However, because pathogens induce changes in vector physiology, pathogen status in the vector may impact vector dispersal. In this work, by using flight mills, we assessed the flight performance of Bactericera cockerellithat were infected or not by the plant pathogenic bacterium ‘CandidatusLiberibacter solanacearum’ (CLso), the causal agent of potato zebra chip disease and vein greening in tomato. Bactericera cockerelliperformed short and long-distance flights, but CLso infection status affected the propensity to engage in long flights. CLso-free insects engaged in long flights significantly more often (57%) compared to CLso infected insects (25%). Average distance dispersed for long flyers was 185.33 m for CLso-free insects and 122.99 m for insects infected with CLso. However, distance dispersed was not statistically different by pathogen status of the vector. Maximal flight capacity recorded was 980 m. Overall, our data suggest that CLso reduces the propensity to engage in long distance flights. Our results can be utilized to fine-tune strategies to mitigate CLso establishment in new areas.