Publications

4364

Summary Uncultivated microbial clades (‘microbial dark matter’) are inferred to play important but uncharacterized roles in nutrient cycling. Using Antarctic lake (Ace Lake, Vestfold Hills) metagenomes, 12 metagenome‐assembled genomes (MAGs; 88%–100% complete) were generated for four ‘dark matter’ phyla: six MAGs from Candidatus Auribacterota (=Aureabacteria, SURF‐CP‐2), inferred to be hydrogen‐ and sulfide‐producing fermentative heterotrophs, with individual MAGs encoding bacterial microcompartments (BMCs), gas vesicles, and type IV pili; one MAG (100% complete) from Candidatus Hinthialibacterota (=OLB16), inferred to be a facultative anaerobe capable of dissimilatory nitrate reduction to ammonia, specialized for mineralization of complex organic matter (e.g. sulfated polysaccharides), and encoding BMCs, flagella, and Tad pili; three MAGs from Candidatus Electryoneota (=AABM5‐125‐24), previously reported to include facultative anaerobes capable of dissimilatory sulfate reduction, and here inferred to perform sulfite oxidation, reverse tricarboxylic acid cycle for autotrophy, and possess numerous proteolytic enzymes; two MAGs from Candidatus Lernaellota (=FEN‐1099), inferred to be capable of formate oxidation, amino acid fermentation, and possess numerous enzymes for protein and polysaccharide degradation. The presence of 16S rRNA gene sequences in public metagenome datasets (88%–100% identity) suggests these ‘dark matter’ phyla contribute to sulfur cycling, degradation of complex organic matter, ammonification and/or chemolithoautotrophic CO 2 fixation in diverse global environments.

AbstractCandidatus Liberibacter solanacearum (CLso) transmitted by the carrot psyllid, Bactericera trigonica causes carrot yellows in Israel, and has recently gained much importance due to the excessive economical loss. Understanding the interactions between CLso and the psyllid at the cellular level is fundamental for the disease management. Here, we demonstrate the role of calcium ATPase, cytosolic calcium and most importantly Beclin1 in regulating autophagy and its association with Liberibacter. Presence of CLso generates reactive oxygen species and induces the expression of the detoxification enzymes in the psyllid midguts. CLso also induces the expression of both sarco/endoplasmic reticulum Ca2+ pump (SERCA) and 1,4,5-trisphosphate receptors (ITPR) in the midguts, followed by high levels of calcium in the cytosol. Silencing these proteins individually disrupted the calcium levels in the cytosol leading to direct effects on autophagy and thus on Liberibacter. On the other hand, inhibiting Beclin1-phosphorylation through different calcium induced kinases altered the expression of autophagy and CLso abundance. This study establishes a direct correlation between cytosolic calcium levels, autophagy and CLso in the carrot psyllid midgut.