Publications

4855

Candidatus Liberibacter asiaticus (CLas) is an unculturable, phloem-limited gram-negative bacterium associated with citrus Huanglongbing (HLB) disease in Florida and most other citrus-producing countries around the world. HLB is considered the most destructive disease of citrus and is severely affecting the fruit production worldwide. Natural transmission of CLas occurs by the Asian citrus psyllid (ACP) vector Diaphorina citri. Under greenhouse conditions, the experimental transmission of CLas to non-infected trees usually is accomplished using infected ACP or by grafting infected citrus tissue. CLas was confirmed infecting citrus in Florida in 2005 and many characteristics of the disease have been described. However, the transmission of CLas for controlled greenhouse studies is often prob lematic and poorly understood. Due the complexity in maintenance of ACP colonies for controlled vector transmission, the experimental infection of new plants is accomplished primarily by grafting, but several factors may influence the reliability of this method. This study evaluates the propagation and transmission efficiency of CLas using graft inoculation methods under greenhouse conditions. Three experiments were conducted for with graft inoculation: 1) seedlings of 12 cultivars; 2) ‘Tango’ mandarin on 13 rootstock cultivars; and 3) ‘Navel’ orange on 14 rootstock cultivars. Plants were inoculated with buds from infected greenhouse-grown ‘Valencia’ orange plants that were poly merase chain reaction (PCR) positive for CLas and symptomatic for HLB. Three bud pieces were used to inoculate each plant using the inverted-T method.

ABSTRACT We report the draft metagenome-assembled genome (MAG) of “ Candidatus Phytoplasma australasiaticum” strain TBB-AP, obtained from a symptomatic tomato plant collected in Andhra Pradesh, India. This assembly provides a genomic resource for functional and evolutionary studies of phytoplasmas associated with tomato big bud disease.

ABSTRACT Cable bacteria conduct long-distance electron transport in sediments but are not yet isolated in pure culture. We report the metagenome-assembled genome of Candidatus Electrothrix sp. NPCB-01 from Newport Bay, California. This 3.46-Mb genome encodes sulfur oxidation, nitrogen and carbon metabolism, and nickel homeostasis genes, expanding resources for these electroactive microbes.

Abstract Background Spirochetes are the most abundant bacterial group in the hindgut of termites. The largest species, with cell lengths of up to 100 µm, have been provisionally classified in the family “ Pillotinaceae ” based exclusively on morphological traits. However, in the absence of cultured representatives, their phylogenetic position and metabolism remain entirely unknown. Results We investigated phylogeny and metabolic capacities of “pillotinaceous” spirochetes using single-cell techniques, electron microscopy, and fluorescence in situ hybridization. All sequences of large spirochetes obtained from various termites fell into four distinct, well-supported clusters within the family Breznakiellaceae . Based on ultrastructural features, three of the clusters were assigned to the genera Pillotina , Hollandina , and the newly established genus Hollandinoides; a fourth cluster was tentatively assigned to the genus Clevelandina . Functional analysis of the single-cell genomes of Pillotina corrugata sp. nov., Hollandina grandis sp. nov., and Hollandinoides gharagozlouae gen. nov. sp. nov., combined with comparative genomics of other uncultured relatives, demonstrated differences in the capacity to degrade cellulose, hemicelluloses, and dextrins. While members of the genus Pillotina have a fermentative metabolism, members of the other genera encode a Wood–Ljungdahl pathway and, in the case of Hollandina , a group-III nitrogenase, suggesting roles in reductive acetogenesis and nitrogen fixation. Conclusions Our results provide the first molecular data on pillotinaceous spirochetes. We show that the three genera covered in our study belong to the family Breznakiellaceae , which harbors the majority of termite-gut spirochetes. Comparative genome analysis indicated that the large spirochetes in termite guts have distinct roles in symbiotic digestion.

<p>Huanglongbing (HLB), caused by <em>Candidatus </em>Liberibacter asiaticus (CLas), continues to challenge citrus production in Saudi Arabia. Although HLB is widespread, there is still limited understanding of how temperature, season, host species, and the type of tissue sampled influence the reliability of CLas detection. In this regard, 123 CLas-positive samples sourced from major citrus-growing areas were analyzed. These samples included data from 4 major citrus species and 4 tissue types. Additionally, cycle threshold<strong> </strong>(Ct) values obtained through quantitative PCR for each sample were used to examine how climate and CLas interact in bacterial detection. As lower Ct values indicate higher bacterial abundance, an analysis of covariance (ANCOVA) was conducted to assess the influence of season, tissue type, citrus species, and average seasonal temperature on Ct values. The results demonstrated significant differences among tissue types, with petiole and midrib tissues exhibiting consistently lower Ct values. Additionally, lower Ct values were observed in spring and autumn, and higher Ct values in warmer summers and colder winters, based on average temperatures. Among the citrus species, only <em>Citrus limon</em> illustrated a prominent increase in CLas levels as temperatures increased. CLas levels in <em>C. limon</em> showed only minor fluctuations with temperature. Taken together, these results indicated that temperature gradients strongly shape CLas population levels in Saudi Arabia and influence the reliability of pathogen detection. Considering climatic context, along with tissue type and season can substantially improve sampling strategies and enhance the effectiveness of HLB monitoring programs in arid and semi-arid citrus production systems.</p>

Abstract ‘Candidatus Mycoplasma haemolamae’ (CMhl) is a hemotropic bacterium infecting South American Camelids (SAC), whose epidemiology and clinical significance are still not fully elucidated. This study investigated CMhl by qPCR in blood samples of alpacas ( Vicugna pacos ) and llamas ( Lama glama ) in Italy in 2021–2024, characterizing CMhl haplotypes based on partial 16 S rRNA sequences and defining haematological findings in a subset of CMhl-infected animals. Statistical analysis was performed to detect potential risk factors associated with CMhl positivity. Out of 206 animals (200 alpacas and 6 llamas), CMhl was detected by qPCR in 88 (42.7%) animals. CMhl haplotype #1 and #2 were detected in 42.2% and 0.5% of the animals, respectively. Binary logistic regression analysis showed that higher CMhl positivity was significantly associated with larger herd size ( P  = 0.011), Northern Italy area of origin ( P  = 0.031) and warmer seasons ( P  = 0.003). The detection of two CMhl haplotypes confirms the high diffusion of CMhl in SAC farmed in Italy. Results confirm that CMhl usually causes subclinical infections, suggesting that antimicrobial treatment is likely not necessary based on qPCR positivity alone. Results focusing on the association of CMhl positivity with warm temperatures and large herd size suggest the need of further studies on the genetic features, epidemiology and immune response in CMhl-positive SAC from Italy, with emphasis on understanding potential vector transmission.