Publications

4620

Abstract Marine 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 The 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.

The beet leafhopper Circulifer tenellus is an important pest of agricultural crops in the United States, where it transmits beet curly top virus, beet leafhopper-transmitted virescence agent phytoplasma, and Spiroplasma citri to numerous crops, affecting yield and quality. Each of these pathogens have been linked to serious disease outbreaks within Washington State in the past century. To mitigate the risk of disease, growers target the beet leafhopper in their insect pest management programs. Knowledge of pathogen prevalence in beet leafhopper populations could help growers make better management decisions, but timely diagnostics is required. Four new assays were developed for the rapid detection of the beet leafhopper-associated pathogens. These include two assays that detect Beet leafhopper transmitted virescence agent (a PCR and a real-time PCR SYBR green assay), a duplex PCR assay that simultaneously detects beet curly top virus and Spiroplasma citri, and a multiplex real-time PCR assay for the simultaneous detection of all three pathogens. The screening of dilution series generated from plant total nucleic acid extracts with these new assays typically led to detection at levels 10- to 100-fold more sensitive than the conventional PCR assays currently used. These new tools will allow the rapid detection of beet leafhopper-associated pathogens in both plant and insect specimens and will have the potential to be used in diagnostic laboratories seeking to disseminate fast and accurate results to growers for implementation in their insect pest monitoring programs.

As hemp ( Cannabis sativa) emerges as a commercial crop in Nevada, mild to severe abnormal growth has been observed from many plants in commercial fields throughout the growing season. Affected plants exhibited a group of symptoms typically including stunting, leaf yellowing, excessive apical branching, clusters of witches’ broom, leaf rolling upwards, and leaf mottling and mosaic. These symptoms mostly showed up together in a plant or a crop and are defined here as abnormal growth syndrome (AGS). Between 2017 and 2019, the Nevada State Plant Pathology and Molecular Diagnostic Lab received 67 symptomatic hemp samples from Nevada for diagnosis, and ‘ Candidatus Phytoplasma trifolii’ was detected in 14 samples (21%). To investigate additional biotic agents associated with AGS, PCR products generated by primers P1/P7 were cloned into a pGEM-T vector and sequenced, and Spiroplasma citri DNA was found in two samples (3%). All 67 DNA samples were further tested for beet curly top virus (BCTV), and 57 samples (85%) were found to be infected by BCTV. Twelve samples (18%) were coinfected by both ‘ Ca. Phytoplasma trifolii’ and BCTV, and two (3%) were coinfected by S. citri, ‘ Ca. Phytoplasma trifolii’, and BCTV. The findings suggest that BCTV is the most prevalent pathogen causing the hemp abnormal growth in Nevada, but ‘ Ca. Phytoplasma trifolii’ and S. citri may also contribute to the severity and complexity of symptoms. Thus, hemp abnormal growth can be attributed to single, dual, or triple infections of these three leafhopper-vectored mollicutes and virus. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Abstract Symbiotic bacteria can alter host biology by providing protection from natural enemies, or alter reproduction or vectoral competence. Symbiont‐linked control of vector‐borne disease in Anopheles has been hampered by a lack of symbioses that can establish stable vertical transmission in the host. Previous screening found the symbiont ‘ Candidatus Tisiphia’ in Anopheles plumbeus , an aggressive biter and potential secondary vector of malaria parasites and West Nile virus. We screened samples collected over 10‐years across Germany and used climate databases to assess environmental influence on incidence. We observed a 95% infection rate, and that the frequency of infection did not fluctuate with broad environmental factors. Maternal inheritance is indicated by presence in the ovaries through FISH microscopy. Finally, we assembled a high‐quality 1.6 Mbp draft genome of ‘ Ca . Tisiphia’ to explore its phylogeny and potential metabolic competence. The infection is closely related to strains found in Culicoides biting midges and shows similar patterns of metabolism, providing no evidence of the capacity to synthesize B‐vitamins. This infection offers avenues for onward research in anopheline mosquito symbioses. Additionally, it provides future opportunity to study the impact of ‘ Ca . Tisiphia’ on natural and transinfected hosts, especially in relation to reproductive fitness and vectorial competence and capacity.

Abstract Marine sediments comprise one of the largest environments on the planet, and their microbial inhabitants are significant players in global carbon and nutrient cycles. Recent studies using metagenomic techniques have shown the complexity of these communities and identified novel microorganisms from the ocean floor. Here, we obtained 77 metagenome-assembled genomes (MAGs) from the bacterial phylum Armatimonadota in the Guaymas Basin, Gulf of California, and the Bohai Sea, China. These MAGs comprise two previously undescribed classes within Armatimonadota, which we propose naming Hebobacteria and Zipacnadia. They are globally distributed in hypoxic and anoxic environments and are dominant members of deep-sea sediments (up to 1.95% of metagenomic raw reads). The classes described here also have unique metabolic capabilities, possessing pathways to reduce carbon dioxide to acetate via the Wood-Ljungdahl pathway (WLP) and generating energy through the oxidative branch of glycolysis using carbon dioxide as an electron sink, maintaining the redox balance using the WLP. Hebobacteria may also be autotrophic, not previously identified in Armatimonadota. Furthermore, these Armatimonadota may play a role in sulfur and nitrogen cycling, using the intermediate compounds hydroxylamine and sulfite. Description of these MAGs enhances our understanding of diversity and metabolic potential within anoxic habitats worldwide.

AbstractThe bacterium Candidatus Liberibacter asiaticus (CLas) causes citrus Huanglongbing disease. Our understanding of the pathogenicity and biology of this microorganism remains limited because CLas has not yet been cultivated in artificial media. Its genome is relatively small and encodes approximately 1136 proteins, of which 415 have unknown functions. Here, we use a high-throughput yeast-two-hybrid (Y2H) screen to identify interactions between CLas proteins, thus providing insights into their potential functions. We identify 4245 interactions between 542 proteins, after screening 916 bait and 936 prey proteins. The false positive rate of the Y2H assay is estimated to be 2.9%. Pull-down assays for nine protein-protein interactions (PPIs) likely involved in flagellar function support the robustness of the Y2H results. The average number of PPIs per node in the CLas interactome is 15.6, which is higher than the numbers previously reported for interactomes of free-living bacteria, suggesting that CLas genome reduction has been accompanied by increased protein multi-functionality. We propose potential functions for 171 uncharacterized proteins, based on the PPI results, guilt-by-association analyses, and comparison with data from other bacterial species. We identify 40 hub-node proteins, including quinone oxidoreductase and LysR, which are known to protect other bacteria against oxidative stress and might be important for CLas survival in the phloem. We expect our PPI database to facilitate research on CLas biology and pathogenicity mechanisms.