Publications

4366

Most of the microorganisms responsible for vector-borne diseases (VBD) have hematophagous arthropods as vector/reservoir. Recently, many new species of microorganisms phylogenetically related to agents of VBD were found in a variety of aquatic eukaryotic hosts; in particular, numerous new bacterial species related to the genus Rickettsia (Alphaproteobacteria, Rickettsiales) were discovered in protist ciliates and other unicellular eukaryotes. Although their pathogenicity for humans and terrestrial animals is not known, several indirect indications exist that these bacteria might act as etiological agents of possible VBD of aquatic organisms, with protists as vectors. In the present study, a novel strain of the Rickettsia-Like Organism (RLO) endosymbiont “Candidatus (Ca.) Trichorickettsia mobilis” was identified in the macronucleus of the ciliate Paramecium multimicronucleatum. We performed transfection experiments of this RLO to planarians (Dugesia japonica) per os. Indeed, the latter is a widely used model system for studying bacteria pathogenic to humans and other Metazoa. In transfection experiments, homogenized paramecia were added to food of antibiotic-treated planarians. Treated and non-treated (i.e. control) planarians were investigated at day 1, 3, and 7 after feeding for endosymbiont presence by means of PCR and ultrastructural analyses. Obtained results were fully concordant and suggest that this RLO endosymbiont can be transiently transferred from ciliates to metazoans, being detected up to day 7 in treated planarians’ enterocytes. Our findings might offer insights into the potential role of ciliates or other protists as putative vectors for diseases caused by Rickettsiales or other RLOs and occurring in fish farms or in the wild.

AbstractThis study reveals that the abundance of the filament Kouleothrix (Eikelboom type 1851) correlated positively with poor settleability of activated sludge biomass in a Japanese full-scale nutrient removal wastewater treatment plant sampled over a one-year period. 16S rRNA amplicon sequence data confirmed that Kouleothrix was the dominant filament in the plant, with a relative abundance of 3.06% positively correlated with sludge volume index (SVI) (R = 0.691). Moreover, Kouleothrix (type 1851) appeared to form interfloc bridges, typical of bulking sludge, regardless of season. Together with earlier studies that indicated the responsibility of Kouleothrix (type 1851) on bulking events, these data suggest that their high relative abundances alone may be responsible for sludge bulking. 16S rRNA qPCR data for this filament showed changes in its relative abundance correlated with changes in several operational parameters, including mixed liquor temperature, sludge retention time, and suspended solids concentration, and it may be that manipulating these may help control Kouleothrix bulking.

A flagellate, rod–shaped bacterium designated strain M15T was isolated from rice roots. Phylogenetic analysis based on the sequences of the 16S rRNA, housekeeping genes and genomes showed that the isolate belonged to the genus Rhizobium, with the highest 16S rRNA similarity to Rhizobium radiobacter LMG140T (99.64%) and Rhizobium pusense NRCPB10T (99.36%), respectively. The complete genome of the strain M15T has a 59.28% G+C content, and the highest average nucleotide identity (ANI) and DNA-DNA relatedness (DDH) values were obtained with R. radiobacter LMG140T (88.11%, 54.80%), R. pusense NRCPB10T (86.00%, 53.00%) and R. nepotum 39/7T (88.80%, 49.80%), respectively. Plant growth-promoting characteristics tests showed that the strain M15T produced siderophore, 1–aminocyclopropane–1–carboxylate (ACC) deaminase and indole-3-acetic acid (IAA) and also produced some secondary metabolites according to the analysis of the comparative genomes. Based on the data mentioned above, we proposed that the strain M15T represented a novel species of the genus Rhizobium, named Rhizobium oryzihabitans sp. nov. The type strain is M15T (=JCM 32903T  = ACCC 60121T), and the strain M15T can be a novel biofertilizer Rhizobium to reduce the use of synthetic fertilizers for plant growth promotion.

Bois noir (BN), associated with ‘Candidatus Phytoplasma solani’ (CaPsol), is the most widespread disease of the grapevine yellows complex worldwide. In this work, BN epidemiology was investigated in a case study vineyard where an unusual CaPsol strain, previously detected only in other host plants, was found to be prevalent in grapevine. Experimental activities included: symptom observation; sampling of symptomatic vines, Auchenorrhyncha specimens, and weeds; molecular detection and typing of CaPsol strains; statistical analyses for determining possible relationships between CaPsol relative concentration, strain type, and symptom severity. Among insects, Reptalus quinquecostatus was the most abundant and was found to be highly infected by CaPsol, while Hyalesthes obsoletus, the main CaPsol vector, was not caught. Moreover, R. quinquecostatus harbored CaPsol strains carrying uniquely the stamp sequence variant St10, also identified as prevalent in vines and in the majority of weeds, and all the secY variants identified in the vineyard. Statistical analyses revealed that CaPsol strains carrying the St10 variant are not associated with severe symptoms, suggesting their possible moderate virulence. Based on such evidence, a new BN epidemiological pattern related to these CaPsol strains and involving grapevine, R. quinquecostatus, and/or weeds is proposed. Furthermore, the possible presence of other players (vectors and weeds) involved in CaPsol transmission to grapevines was highlighted.

Nowadays, Huanglongbing (HLB) disease, associated with Candidatus Liberibacter asiaticus (CLas), seriously affects citriculture worldwide, and no cure is currently available. Transcriptomic analysis of host–pathogen interaction is the first step to understand the molecular landscape of a disease. Previous works have reported the transcriptome profiling in response to HLB in different susceptible citrus species; however, similar studies in tolerant citrus species, including Mexican lime, are limited. In this work, we have obtained an RNA-seq-based differential expression profile of Mexican lime plants challenged against CLas infection, at both asymptomatic and symptomatic stages. Typical HLB-responsive differentially expressed genes (DEGs) are involved in photosynthesis, secondary metabolism, and phytohormone homeostasis. Enrichment of DEGs associated with biotic response showed that genes related to cell wall, secondary metabolism, transcription factors, signaling, and redox reactions could play a role in the tolerance of Mexican lime against CLas infection. Interestingly, despite some concordance observed between transcriptional responses of different tolerant citrus species, a subset of DEGs appeared to be species-specific. Our data highlights the importance of studying the host response during HLB disease using as model tolerant citrus species, in order to design new and opportune diagnostic and management methods.

AbstractHuanglongbing, a highly destructive disease of citrus species, is associated with a fastidious, gram-negative, phloem-limited bacteria (Candidatus Liberibacter spp.). In Florida, the causative agent of Huanglongbing (HLB) is C. Liberibacter asiaticus (CLas) and it is transmitted by the insect vector, Asian citrus psyllid (Diaphorina citri Kuwayama). Previous investigations have revealed systemic infection of CLas with an erratic and uneven distribution of pathogen in tree phloem. However, previous investigations did not consider the potential impact of plant vegetative growth on presence/absence of CLas in planta. Our objectives were to determine: 1) the effect of vegetative growth of Citrus sinensis (L.) Osbeck cv Valencia on detection of CLas in mature leaves, and 2) the impact of CLas inoculation frequency on progression of CLas titer in citrus leaves through the first year of infection. Temporal dynamics of CLas detection were associated with vegetative flush growth. Surprisingly, there was no difference in CLas titer detected between plants exposed to infected vectors for a one-time 7 d inoculation access period, as compared with plants exposed to continuously breeding CLas-infected insects over the course of an entire year of plant infection. Our results suggest that the CLas bacterium is transported through phloem during annual movement of carbon compounds needed for vegetative plant growth, including transportation from roots to mature leaves. These results highlight the importance of vegetative growth on temporal dynamics of CLas in citrus, and suggest a critical role of the sink-source interaction on presence/absence of CLas in leaves.

Huanglongbing (HLB, citrus greening disease) in the major citrus-producing states of the United States is associated with Candidatus Liberibacter asiaticus (CLas), which is vectored by the Asian citrus psyllid (ACP). Surveys were conducted in Texas from 2007 to 2017 to assess the prevalence and titer of CLas in ACPs and citrus trees. ACP and citrus leaf tissue samples were collected from suspect trees in residential areas and commercial groves (orchards) and assayed for CLas by quantitative PCR. CLas detection in ACPs (2011) preceded that of citrus trees (2012) by several months. Annual incidences of CLas-positive ACPs and leaf tissue followed an exponential growth pattern over the survey period, varying from 0.03 to 28.7% in ACPs and 0.6 to 36.5% in citrus trees. There was a significant and positive relationship between the monthly incidences of CLas-positive ACP and leaf tissue samples. The proportion of HLB detection sites also increased with time, reaching 26 and 40% of commercial groves and residential sites, respectively, by 2017. Seasonal variations were observed in the incidences of CLas-positive ACPs and citrus trees such that significantly more CLas-positive ACPs and trees were recorded during the fall and winter of a given year relative to the hot summer. A temporal analysis of the class distribution of cycle threshold values revealed a trend of increased bacterial accumulation in ACPs and trees over time, with the trend more pronounced for the former than the latter host type. These findings provide a comprehensive insight into the ongoing CLas/HLB epidemic in Texas, with potential lessons for California and other citrus-producing areas where the disease is not yet established.