Publications

4489

AbstractThe black curry leaf psyllid, Diaphorina communis, is a host of the citrus pathogen, ‘Candidatus Liberibacter asiaticus’ (‘CLas’). However, there is a paucity of information on its biology; hence, this study was conducted to evaluate survival and development on citrus, in this instance mandarin (Citrus reticulata) and curry leaf (Bergera koenigii), and transmission of ‘CLas’. Given its similarity with the Asian citrus psyllid (Diaphorina citri), sequences of the COI and 16S genes were examined to see if they could distinguish molecularly between nymphs of these two species. Field and laboratory experiments showed that D. communis nymphs transferred to mandarin branches failed to survive. Adults could survive on flush growth of ‘CLas’‐infected mandarin trees; however, little oviposition took place, and the single resulting nymph did not survive to the second instar. These observations suggest that D. communis does not develop, or rarely develops on mandarin and possibly other Citrus spp. Curry leaf appears to be its preferred host, and complete development can take place, possibly exclusively, on this species. Studies on acquisition of ‘CLas’ by D. communis and possible transmission assessed in 2014 and 2015 using greenhouse‐grown curry leaf and mandarin seedlings with naturally infected mandarin stumps as a source of ‘CLas’ indicated a low acquisition rate of ‘CLas’. In addition, although D. communis can acquire ‘CLas’, it either cannot transmit it or transmission is limited, and the pathogen may not multiply within the insect. Phylogenetic analyses indicate that differences in COI and 16S regions may prove useful for differentiating between early instar D. communis and D. citri nymphs when fifth instar nymphs and adults are not present on host plants.

Summary Holosporales are an alphaproteobacterial lineage encompassing bacteria obligatorily associated with multiple diverse eukaryotes. For most representatives, little is known on the interactions with their hosts. In this study, we characterized a novel Holosporales symbiont of the ciliate Paramecium polycaryum . This bacterium inhabits the host cytoplasm, frequently forming quite large aggregates. Possibly due to such aggregates, host cells sometimes displayed lethal division defects. The symbiont was also able to experimentally stably infect another Paramecium polycaryum strain. The bacterium is phylogenetically related with symbionts of other ciliates and diplonemids, forming a putatively fast‐evolving clade within the family Holosporaceae . Similarly to many close relatives, it presents a very small genome (<600 kbp), and, accordingly, a limited predicted metabolism, implying a heavy dependence on Paramecium , thanks also to some specialized membrane transporters. Characterized features, including the presence of specific secretion systems, are overall suggestive of a mild parasitic effect on the host. From an evolutionary perspective, a potential ancestral trend towards pronounced genome reduction and possibly linked to parasitism could be inferred, at least among fast‐evolving Holosporaceae , with some lineage‐specific traits. Interestingly, similar convergent features could be observed in other host‐associated lineages, in particular Rickettsiales among Alphaproteobacteria .

Summary Anaerobic oxidation of methane (AOM) is a microbial process degrading ample methane in anoxic environments, and Ca. Methanoperedens mediated nitrate‐ or metal‐reduction linked AOM is believed important in freshwater systems. This work, via 16S rRNA gene diversity survey and 16S rRNA quantification, found abundant Ca. Methanoperedens along with iron in the cold Zoige wetland at Tibetan Plateau. The wetland soil microcosm performed Fe(III) reduction, rather than nitrate‐ nor sulphate‐reduction, coupled methane oxidation (3.87 μmol d −1 ) with 32.33 μmol Fe(II) accumulation per day at 18°C, but not at 30°C. A metagenome‐assembled genome (MAG) recovered from the microcosm exhibits ~74% average nucleotide identity with the reported Ca. Methanoperedens spp. that perform Fe(III) reduction linked AOM, thus a novel species Ca. Methanoperedens psychrophilus was proposed. Ca. M. psychrophilus contains the whole suite of CO 2 reductive methanogenic genes presumably involving in AOM via a reverse direction, and comparative genome analysis revealed its unique gene categories: the multi‐heme clusters (MHCs) cytochromes, the S‐layer proteins highly homologous to those recovered from lower temperature environments and type IV pili, those could confer Ca. M. psychrophilus of cold adaptability. Therefore, this work reports the first methanotroph implementing AOM in an alpine wetland.

AbstractThe Asian citrus psyllid, Diaphorina citri is an invasive insect 1 and a vector of ’Candidatus Liberibacter asiaticus’ (CLas), a bacterium whose growth in Citrus species results in citrus greening disease 2,3. Methods to enrich and sequence CLas from D. citri often rely on biased genome amplification 4 and nevertheless contain significant quantities of host DNA 5,6. To overcome these hurdles, we developed a simple pre-treatment DNase and filtration (hereafter PDF) protocol to directly sequence CLas and the complete, primarily uncultivable, microbiome from D. citri adults. The PDF protocol yielded CLas abundances upwards of 60% and enabled detection of 156 genetic variants in these strains compared to progenitor strains in Florida, which included prophage encoding regions with key functions in CLas pathogenesis, putative antibiotic resistance loci, and a single secreted effector. These variants suggest laboratory propagation of CLas may result in different phenotypic trajectories among laboratories, and may confound CLas physiology or therapeutic design and evaluation if these differences remain undocumented. Finally, we obtained genetic signatures affiliated with Citrus nuclear and organellar genomes, entomopathogenic fungal mitochondria, and commensal bacteria from laboratory-reared and field-collected D. citri adults. Hence, the PDF protocol can inform agricultural management strategies related to pathogen evolution 7, insect microbiome surveillance 8, antibiotic resistance screening 9, and gut content analysis 10.