Publications

4855

‘ Candidatus Liberibacter asiaticus’ ( C Las), the causal agent of citrus huanglongbing, is transmitted by the Asian citrus psyllid Diaphorina citri . While C Las-positive ( C Las+) females exhibit increased fecundity and metabolic demands, their neuroendocrine regulation mechanisms remain unclear. We propose C Las manipulates dopamine (DA) signaling to enhance psyllid fecundity and C Las proliferation. Metabolomics revealed elevated DA in C Las+ females. Silencing DA synthesis genes and receptor DcDop2 via RNAi reduced lipid reserves, fecundity, and ovarian C Las titers. Through combined in vivo and in vitro experiments, we demonstrated that the microRNA miR-31a suppresses DcDop2 expression by binding to its 3’ untranslated region. Overexpression of miR-31a resulted in decreased DcDop2 expression and C Las titers in the ovaries, eliciting phenotypic defects akin to DcDop2 knockdown. Furthermore, DcDop2 knockdown and miR-31a overexpression reduced juvenile hormone (JH) levels and adipokinetic hormone (AKH) signaling in fat bodies and ovaries. Consequently, C Las regulates the DA- DcDop2 signaling axis to improve D. citri lipid metabolism and fecundity, while simultaneously promoting its replication. These findings reveal a coevolution between C Las proliferation and ovarian development in the insect host. This discovery enhances our understanding of the molecular interplay between plant pathogens and vector insects and offers novel targets and strategies for HLB field management.

‘ Candidatus Liberibacter asiaticus’ ( C Las), the causal agent of citrus huanglongbing, is transmitted by the Asian citrus psyllid Diaphorina citri . While C Las-positive ( C Las+) females exhibit increased fecundity and metabolic demands, their neuroendocrine regulation mechanisms remain unclear. We propose C Las manipulates dopamine (DA) signaling to enhance psyllid fecundity and C Las proliferation. Metabolomics revealed elevated DA in C Las+ females. Silencing DA synthesis genes and receptor DcDop2 via RNAi reduced lipid reserves, fecundity, and ovarian C Las titers. Through combined in vivo and in vitro experiments, we demonstrated that the microRNA miR-31a suppresses DcDop2 expression by binding to its 3’ untranslated region. Overexpression of miR-31a resulted in decreased DcDop2 expression and C Las titers in the ovaries, eliciting phenotypic defects akin to DcDop2 knockdown. Furthermore, DcDop2 knockdown and miR-31a overexpression reduced juvenile hormone (JH) levels and adipokinetic hormone (AKH) signaling in fat bodies and ovaries. Consequently, C Las regulates the DA- DcDop2 signaling axis to improve D. citri lipid metabolism and fecundity, while simultaneously promoting its replication. These findings reveal a coevolution between C Las proliferation and ovarian development in the insect host. This discovery enhances our understanding of the molecular interplay between plant pathogens and vector insects and offers novel targets and strategies for HLB field management.

Chokecherry (Prunus virginiana L.) is a native shrub that is widely found across North America and is a host of ‘Candidatus Phytoplasma pruni’ associated with X-disease of stone fruits. This pathogen is of major concern to U.S. cherry and peach growers, with the most recent and ongoing outbreak in the Pacific Northwest causing major economic harm. To investigate the role of chokecherry as a potential reservoir and source of orchard-associated strains, we surveyed wild chokecherry trees across 12 U.S. states, and compared the strains present to those in commercially cultivated Prunus species. Approximately 47% of chokecherry sampled tested positive for a ‘Ca. P. pruni’-related strain and phylogenetic analysis revealed high strain diversity, including six distinct clades and four newly identified lineages. In contrast, ‘Ca. P. pruni’ strains isolated from cultivated cherry and peach trees exhibited lower diversity and were infected by known disease outbreak-associated strains such as NWX. These data suggest limited transmission between wild and cultivated hosts in the western U.S., with patterns indicating spillover from orchards into nearby chokecherry populations rather than the reverse. However, in states east of the Rocky Mountains, chokecherry likely functions as a reservoir for orchard infections.

Abstract A comprehensive polyphasic taxonomic strategy was applied to the systematic characterization of strain DNPG3 T , which was isolated from the river Ganges, Hooghly, West Bengal, India. The Gram-positive, halotolerant, heavy-metal-tolerant strain exhibited the ability to degrade p -nitrophenol (PNP). Cellular fatty acid analysis revealed that the predominant components were anteiso-C 15:0 (24.61%), C 11:0 (21.06%), iso-C 16:0 (11.89%), C 16:0 (11.58%), and anteiso-C 17:0 (11.24%). Notably, the presence of C 11:0 , C 10:0 2-OH as major fatty acids differentiate strain DNPG3 T from its closely related members of the genus Brachybacterium . The predominant respiratory quinone was identified as menaquinone-7 (MK-7). Analysis of 16S rRNA gene sequence indicated that B. zhongshanense strain JB T was the closest relative of DNPG3 T , sharing 97.08% sequence similarity. Genome-based ANI value calculated using the EzBioCloud server revealed that B. zhongshanense JCM 15471 T was the closest genomic relative (85.49%). These values were further substantiated by digital DNA–DNA hybridization (dDDH) estimates calculated using the GGDC server. Taxonomic assignment using the GTDB database further indicated that strain DNPG3 T constitutes a previously unrecognized species within the genus Brachybacterium . Genome analysis of strain DNPG3 T identified eleven genomic islands, along with a rich repertoire of 194 carbohydrate-active enzyme (CAZyme) families, comprising 95 glycoside hydrolases and 53 glycosyltransferases. In addition, five biosynthetic gene clusters were detected. Collectively, these genomic features indicate the involvement of horizontal gene transfer events and highlighted the pronounced metabolic versatility of the strain, underscoring its potential for industrial enzyme production and secondary metabolite biosynthesis. Pan-genome analysis further indicates that the Brachybacterium pan-genome is open, reflecting substantial genetic diversity and ongoing gene acquisition within the genus. Comprehensive biochemical, physiological, chemotaxonomic, and phylogenetic analyses supported the assignment of strain DNPG3 T to the genus Brachybacterium while clearly distinguishing it from all currently described species within the genus. Accordingly, strain DNPG3 T was proposed to represent a novel species, for which the name Brachybacterium netajii sp. nov. is suggested. The type strain was DNPG3 T (= MTCC13125 T ).

ABSTRACT The Sphaerotilus-Leptothrix group of bacteria includes one of the first described microorganisms, Leptothrix ochracea , an uncultured type strain, plus isolates of Leptothrix and Sphaerotilus . This group is unified by the ability to form sheaths and oxidize metals, although L. ochracea exhibits obvious ecological, morphological, and functional differences from the rest of Sphaerotilus-Leptothrix . Recently, there have been calls to combine the group into one genus, Sphaerotilus ; however, these studies lacked adequate genomic representation of L. ochracea . Here, we present a comprehensive comparative genomic analysis of the Sphaerotilus-Leptothrix group, including expanded representation of L. ochracea , a closely related novel species, Leptothrix toolikensis , and two new isolates ( Leptothrix mechoopdaensis ). Analysis of 38 genomes resolves three phylogenetic and functional groups: the ochracea -type Leptothrix (Group 1), the mobilis -type Leptothrix (Group 2), and Sphaerotilus (Group 3). Group 1 genomes form a separate genus based on average nucleotide identity and alignment fraction. The genomes clearly diverge from the rest of Sphaerotilus-Leptothrix in phylogeny, size, and metabolic potential. Group 1 genomes are much smaller (2.59–3.04 Mb) than those of Groups 2 (4.55–6.06 Mb) and 3 (3.94–5.07 Mb), while encoding more metal oxidases and fewer carbohydrate-active enzymes. Group 2 clusters with Group 3 phylogenetically and is similar in organic carbon metabolisms but maintains more metal oxidation genes. Group 2 members lack homogeneity in phenotype and genotype, suggesting that additional isolates and genomes are needed for confident classification. However, Group 1 genomes ( L. ochracea and L. toolikensis ) show clear divergence, precluding their inclusion in Sphaerotilus and supporting the retention of the genus Leptothrix . IMPORTANCE Researchers have long noted differences in metal oxidation, morphology, and ecology among Sphaerotilus-Leptothrix , but longstanding confusion over phylogeny and genus boundaries led to inconsistent taxonomic classification between the two genera. This confusion stems from previous work that used isolates that are unavailable or lost distinguishing traits in culture, and from limited genomic data. Furthermore, the Leptothrix type strain L. ochracea has never been isolated. This study provides molecular evidence that substantiates calls to reassign some Leptothrix members to the genus Sphaerotilus but adds to an emerging body of evidence that Group 1 L. ochracea and now L. toolikensis represent a functionally distinct lineage. While genomic similarity metrics left taxonomic divisions unclear, integrating metabolic potential with phylogeny resolved genus boundaries based on clear functional groupings. This polyphasic approach for delineating genera clarifies longstanding taxonomic confusion and refines our understanding of functional diversity both across and within Sphaerotilus-Leptothrix lineages.