Publications

4795

Abstract Krum.hol.zi.bac.te.ri.o'ta. N.L. neut. n. Krumholzibacterium , type genus of the type class of the phylum; L. neut. pl. n. suff. ‐ota , ending to denote a phylum; N.L. neut. pl. n. Krumholzibacteriota , the phylum of the class Krumholzibacteria. The phylum Candidatus Krumholzibacteriota was proposed to accommodate genomic assemblies of yet‐uncultured microorganisms. The type species, of the genus, Candidatus Krumholzibacterium zodletonense Zgenome0171 T was recovered from an anaerobic, sulfide‐ and sulfur‐rich spring in Southwestern Oklahoma, USA. The phylum comprises one described class, order, family, genus, and species. However, currently available genomes ( n  = 90) in GTDB (release 08‐RS214) are accommodated in 1 class, 6 orders, 8 families, 30 genera, and 58 species. Phylogenetically, the phylum is closely related to Gemmatimonadota and multiple phyla with no cultured representatives ( Ca . Edwardsbacteria, Ca . Eisenbacteria, Ca . Latescibacterota, Ca . Zixibacteria, 4572‐55, ARS69, GCA‐2686955, JAAXHH01, JABDJQ01, JAGLTZ01, JAGLYR01, TA06, TA06_A, and VGIX01); all of which are part of the FCB ( Fibrobacteres , Chlorobia , Bacteroidetes ) superphylum in the Gracilicutes clade. Candidatus Krumholzibacteriota genomes have mainly been recovered from marine, freshwater, engineered, and host‐associated ecosystems. The prevailing in‐situ conditions in sampled habitats, gene content analysis, and the use of predictive machine learning‐based approaches suggest a phylum‐wide preference for anaerobic conditions, mesophilic temperatures, circumneutral pH, and low salinities. Metabolically, the type species of the type genus of the phylum is predicted to be a fermentative anaerobe with preference for amino acids over sugars as substrates. Later studies indicate that some members of the phylum harbor respiratory capacities (dissimilatory sulfate reduction, dissimilatory sulfite reduction, iron‐reduction, and high‐affinity oxygen respiration with a few members possessing the potential for low‐affinity oxygen respiration), while others possess the machinery for anaerobic degradation of aromatic hydrocarbons. Finally, although all members of Candidatus Krumholzibacteriota remain uncultured, a representative of the phylum was enriched in a methane‐ and iron‐fed bioreactor inoculated with Bothnian Sea sediments. Type genus : Candidatus Krumholzibacterium Youssef et al. 2019, CL2.

The Asian citrus psyllid, Diaphorina citri, transmits the putative causal agent of citrus greening disease, ‘ Candidatus Liberibacter asiaticus’. The transmission occurs in a propagative, circulative manner. Specific protein–protein interactions are required for the accomplishment of the transmission process. We employed the far-Western technique, also known as protein overlay assay, and mass spectrometry to identify D. citri proteins that specifically recognize membrane proteins of ‘ Ca. L. asiaticus’. Whole-body protein extracts of D. citri were separated by electrophoresis and blotted onto polyvinylidene difluoride membranes. The membranes were overlayed with sonicated leaf midrib extracts from ‘ Ca. L. asiaticus’-infected citrus plants. The protein complexes were detected using different antibodies against ‘ Ca. L. asiaticus’ membrane proteins and peptidoglycans associated with lipoproteins. By comparison, spots were extracted from a polyacrylamide gel for liquid chromatography-tandem mass spectrometry analysis. Identified proteins included ATP synthase alpha and beta subunits, actin, alpha- and beta-tubulins, transitional endoplasmic reticulum ATPase TER94, 78 kDa glucose-regulated protein, and arginine kinase. These findings emphasize the involvement of energy machinery and muscle proteins in the ‘ Ca. L. asiaticus’– D. citri interactions. Understanding the pathogen–vector interactions will lead to better-designed control strategies based on the interference with specific interactions and/or blocking transmission.

Abstract Phytoplasmas are wall-less plant pathogens characterized by highly reduced genomes and limited metabolic capabilities, leading to an obligate host dependency. Since phytoplasma axenic cultivation has not yet been achieved, genomic approaches are essential to unravelling their biological and pathogenic traits. However, such insights are currently hindered by the scarcity of complete genomes and the lack of data for several clades, as is the case for the quarantine-relevant ‘ Candidatus Phytoplasma phoenicium’ (group 16SrIX-B), the causal agent of the severe stone-fruit disease almond witches’ broom (AlmWB). In this study, we present the complete genome sequence of the Lebanese strain F1A, which consists of a 552,248 bp chromosome with a 24.29% GC content and encodes 450 protein-coding genes. Comparative analyses with 16SrIX group draft genomes revealed high conservation among Lebanese AlmWB strains; however, comparisons with related 16SrIX-C phytoplasmas were limited by their low assembly completeness. Beyond providing a complete reference genome for this phytoplasma group, the F1A chromosome revealed distinct metabolic features. Strain F1A lacks the upper glycolytic pathway, indicating a metabolism that relies on glycerol-3-phosphate uptake and carboxylic acid fermentation. Notably, in addition to the conserved malate-to-acetate pathway, F1A encodes a complete citrate lyase complex, suggesting the potential for citrate utilization. Phylogenetic analysis of the associated 2-hydrocarboxylate symporter revealed the widespread occurrence of two phylogenetically distinct variants in phytoplasmas. Apart from the deduced metabolic capacities, the predicted effector repertoire shows similarities with those of other phytoplasmas, including proteins associated with branch proliferation and witches’ broom symptoms. Overall, these findings link genome reduction to host-dependent carboxylic acid metabolism in a quarantine-relevant phytoplasma, establishing a framework for comparative and functional studies of 16SrIX phytoplasmas and providing a basis for future investigations of AlmWB ecology and pathogenicity.

ABSTRACT The selective autophagy receptor NEIGHBOUR OF BRCA1 (NBR1) is a key regulator of plant immunity, but its role against bacterial pathogens remains poorly understood. Here, we demonstrated that overexpression of CsNBR1 confers citrus resistance to huanglongbing (HLB) caused by ‘ Candidatus Liberibacter asiaticus’ ( C Las). CsNBR1 can interact with multiple virulence effector proteins of C Las, including SDE5115, SDE1, SDE19 and SDE5, leading to their degradation via the autophagic pathway. In addition, expression of CsNBR1 in Nicotiana benthamiana mitigated the leaf curling and dwarfing phenotypes triggered by SDE1 by reducing the protein content of SDE1. These findings reveal that CsNBR1 positively regulates citrus defence against C Las by degrading its effector proteins via selective autophagy, providing both mechanistic insights and a potential target for resistance breeding.