Publications

4674

A Gram-stain-negative, aerobic, capsule-forming strain, designated DAS-389 T , was isolated from soil collected in the Kogelberg Nature Reserve, Western Cape, South Africa. The strain formed small pink colonies, with cells that multiplied by binary division. Optimum growth was observed at 20 °C to 26 °C and pH 5.5 to 6.5, and it tolerated a NaCl concentration up to 1.5% (w/v). DAS-389 T is chemoorganotrophic, with growth substrate preferences for sugars and polysaccharides, including fructose and starch, respectively. The genome of DAS-389 T had a genome size of 4,136,282 bp with an average G+C content of 63.49 mol% and encodes for an assortment of enzymes, carbohydrate metabolic pathways and several genes involved in stress and survival responses. Major fatty acids (>5%) of strain DAS-389 T were iso-C15:0, iso-C17:0, summed feature 3 (C16:1 ω7c and/or C16:1 ω6c) and summed feature 9 (iso-C17:1 ω9c and/or C16:0 10-methyl). Comparative analysis of 16S rRNA gene sequences revealed that strain DAS-389 T shared the highest similarity with Alloacidobacterium dinghuense 4Y35 T (96.6%), followed by Acidipila rosea AP8 T (96.6%) and Paracidobacterium acidisoli 4G-K13T (96.3%). Phylogenetic analysis based on 16S rRNA gene sequences and the whole proteome placed DAS-389 T within a distinct clade, separate from recognized genera in the family Acidobacteriaceae . We therefore propose that strain DAS-389ᵀ represents a novel genus and species, Candidatus Dedyshia acidiphila gen. nov., sp. nov., within the family Acidobacteriaceae , order Terriglobia . The whole-genome sequence of strain DAS-389ᵀ [accession number: JBMGJV000000000 (PRJNA1221820) ] is designated as the nomenclatural type.

Periploca aphylla witches’ broom (PapWB) is a phytoplasma-associated disease first reported in south-western Iran in 2010. Recent observations showed that the disease is spreading to new areas. PapWB phytoplasmas, detected in symptomatic P. aphylla plants, exhibited identical nucleotide sequences in the 1.8 kb PCR amplicon encompassing the 16S rRNA gene, the 16S-23S spacer region and the 5′-end of the 23S rRNA gene. When compared with the reference strains of previously described ‘ Candidatus Phytoplasma’ species, the selected representative strain PapWB-S exhibited the highest 16S rRNA gene sequence identity (98.15%) with salt cedar witches’ broom (SCWB1) phytoplasma, the reference strain of ‘ Ca . P. tamaricis’. Moreover, the sequence identity values for the tufB, rplV-rpsC and secY genes of PapWB-S strain, when compared with those of reference strains of previously described ‘ Ca . Phytoplasma’ species, were below the thresholds adopted for describing new species. Phylogenetic analyses confirmed the close relationship of the strain PapWB-S with SCWB1 followed by other ‘ Ca . Phytoplasma’ species belonging to the ribosomal groups 16SrX, 16SrXX and 16SrXXXIII. Following the revised guidelines for describing ‘ Ca . Phytoplasma’ species, ‘ Ca . P. periplocae’ sp. nov., associated with PapWB disease, is proposed, and the 16S rRNA gene sequence (accessible at GenBank/NCBI accession number OQ819043) is its nomenclatural type.

Abstract “ Candidatus Liberibacter solanacearum” (Lso) is a phloem-limited bacterial pathogen transmitted by psyllid. In the USA, the haplotypes A and B are transmitted by the tomato psyllid, Bactericera cockerelli, and are responsible for economic damage to the solanaceous crop industry. In tomato, haplotypes A and B cause diseases with differing degrees of severity, yet their underlying mechanisms are not well understood. The role that abiotic stress plays in disease development has not been characterized. In the present study, we evaluated whether water stress influenced the development of symptoms associated with these haplotypes in tomato ( Solanum lycopersicum “Moneymaker”). First, pot-grown tomato plants were subjected to either a control or a water-stress regime, then they were assigned to one of three infection treatments (Lso-free, LsoA, or LsoB) under laboratory-controlled conditions. Symptom development was monitored for up to 8 weeks following infection. Results of this experiment revealed that water stress significantly reduced the plant water potential and was the primary driver of reduced height, with infection only having an effect in later weeks. Water stress also increased the detectability of Lso throughout the plant and across three timepoints (weeks 4, 6, and 8 after infection). This increase in Lso-positive tissues suggests that water stress creates a more homogenous distribution of Lso throughout the plant. More noticeably, water stress significantly reduced the severity of the disease associated with haplotype A but not B. Overall, these findings revealed the existence of haplotype-specific interactions between Lso infection and water stress on the tomato health. This work highlights the influence of abiotic factors on plant health.

Ticks are important vectors of bacteria belonging to the order Rickettsiales, several of which are causes zoonotic diseases. Amblyomma triste is the main vector of Rickettsia parkeri , the etiological agent responsible for most cases of human spotted fever rickettsiosis in Argentina. However, information on the circulation of rickettsial agents in protected areas of the La Plata River Hydrographic Basin, a region that includes highly urbanized environments and frequent contact between wildlife, domestic animals and humans, remains limited. The aim of this study was to investigate the presence of rickettsial bacteria in A. triste collected in protected areas of Buenos Aires Province, (La Plata River Hydrographic Basin, Argentina). Between September and December 2021, ticks were collected by vegetation flagging in four protected areas and analyzed individually. Polymerase chain reactions (PCR) for detecting the genus Rickettsia was initially performed using a simple PCR to amplify a variablesized fragment of the 23S-5S rRNA intergenic spacer. An initial PCR was performed with primers for a 16S rRNA fragment for the Anaplasmataceae family. A total of 247 adult ticks were examined. Twelve specimens (4.9%) tested positive for Rickettsia , and sequence analysis confirmed their identity as R. parkeri . Positive ticks were detected in Ciervo de los Pantanos National Park and Campos del Tuyú National Park. In addition, two specimens yielded sequences corresponding to Candidatus Midichloria sp. These findings confirm the presence of R. parkeri in A. triste populations from protected areas of the La Plata River Hydrographic Basin and provide the first evidence of Ca. Midichloria sp. in this tick species in Argentina. The results highlight the need for continued surveillance of tick-borne microorganisms in protected areas located near densely populated regions, where human exposure to infected ticks may occur.

Huanglongbing, a destructive citrus disease of global importance that is also present in Saudi Arabia, is associated with Candidatus Liberibacter asiaticus (CLas) and remains a major threat to citrus production. Although previous studies have documented sequence variation and prophage polymorphism in CLas, broader comparisons of prophage-associated gene content remain limited. In particular, comparative orthogroup analysis of prophage gene-content conservation across geographically structured CLas populations has rarely been explored. In this study, we analyzed 42 CLas prophage genomes from Saudi Arabia and other geographic regions using a comparative orthogroup framework. OrthoFinder assigned 99.1% of predicted proteins (1825 of 1841) to 64 orthogroups, with only 16 genes remaining unassigned. A small number of rare orthogroups restricted to only a few genomes were identified, and no orthogroup was detected in all genomes. Presence–absence analyses supported a predominantly conserved prophage gene repertoire together with a small accessory component, while also indicating that apparent absences should be interpreted in light of mixed assembly status and prophage-region completeness. Saudi Arabian genomes were distributed within the broader global framework and exhibited generally similar gene-content profiles rather than a deeply separated lineage. Functional interpretation of representative orthogroups identified conserved prophage-associated genes related to replication, helicase activity, and phage packaging, whereas variable orthogroups were primarily associated with hypothetical or accessory prophage-related functions. Overall, these results are consistent with a model in which CLas prophage diversification is associated more with sequence-level variation and localized structural differences than with extensive gain or loss of prophage genes. These findings further refine current understanding of CLas genome evolution and highlight conserved prophage-associated targets that may support molecular diagnostics and epidemiological surveillance.