Publications

4561

Abstract

Abstract

ABSTRACT Biogas, a mix of CO 2 , CH 4 and small proportions of other gases, is a biofuel obtained by anaerobic digestion (AD). Biogas production is often considered a black box process, as the role and dynamics of some of the microorganisms involved remain undisclosed. Previous metataxonomic studies in the frame of the MICRO4BIOGAS project ( www.micro4biogas.eu ) revealed that MBA03, an uncharacterised and uncultured bacterial taxon belonging to phylum Bacillota , was very prevalent and abundant in industrial full‐scale AD plants. Despite the efforts, this taxon has not yet been cultivated, which makes the analysis of its taxonomy, ecology and metabolism even more challenging. In the present work, 30 samples derived from anaerobic digesters were sequenced, allowing the reconstruction of 108 metagenome‐assembled genomes (MAGs) potentially belonging to MBA03. According to phylogenetic analyses and genomic similarity indices, MBA03 was classified as a new bacterial order, proposed as ‘ Candidatus Darwinibacteriales’ ord. nov., which includes ‘ Candidatus Darwinibacter acetoxidans’ gen. nov., sp. nov. of ‘ Candidatus Darwinibacteriaceae’ fam. nov., along with ‘ Candidatus Wallacebacter cryptica’ gen. nov., sp. nov. of the ‘ Candidatus Wallacebacteriaceae’ fam. nov. Ecotaxonomic studies determined that AD processes are the main ecological niche of ‘ Candidatus Darwinibacteriales’. Moreover, metabolic predictions identified Darwinibacteraceae members as putative syntrophic acetate‐oxidising bacteria (SAOB), as they encode for the reversed Wood–Ljungdahl (W–L) pathway coupled to the glycine cleavage system. This suggests that Darwinibacteraceae members could work in collaboration with hydrogenotrophic methanogenic archaea to produce methane in industrial biogas plants. Overall, our findings present ‘ Candidatus Darwinibacteriales’ as a potential key player in anaerobic digestion and pave the way towards the complete characterisation of this newly described bacterial taxon, which has not yet been cultured.

Abstract Bactericera maculipennis (Crawford) and Bactericera cockerelli (Šulc) (Hemiptera: Triozidae) share hosts within the Solanaceae and Convolvulaceae (Solanales), and both are associated with “Candidatus Liberibacter solanacearum” (Lso). Lso, transmitted by B. cockerelli, causes diseases in solanaceous crops including zebra chip disease of potato. Up to 50% of B. maculipennis adults also harbor Lso, but transmission of Lso to plants by this psyllid has not been confirmed yet. The only documented field host of B. maculipennis in the Pacific Northwest is Convolvulus arvensis L. (Convolvulaceae) but diagnostic methods fail to detect Lso in leaves of this plant. It is therefore unclear how Lso persists within B. maculipennis populations. We surveyed species of Convolvulaceae and Solanaceae for B. maculipennis and report a widespread association between B. maculipennis and Lso throughout the western United States. Diagnostic polymerase chain reaction failed to detect Lso from leaves of C. arvensis yet readily detected Lso from stems where B. maculipennis nymphs tend to feed. Bactericera maculipennis transmitted Lso to species of Convolvulaceae in greenhouse experiments, confirming vector competency. We report high rates of Lso infection in populations of both B. maculipennis and B. cockerelli occurring on C. arvensis, but occurrence of B. cockerelli on C. arvensis was limited to autumn months only and with very low populations. Results suggest C. arvensis is a non-crop reservoir of Lso but do not suggest that B. maculipennis is a direct threat to solanaceous crops or that C. arvensis is a major source of Lso-infected B. cockerelli colonizing potato fields.