Publications

4517

AbstractCandidatusLiberibacter asiaticus (CLas) is one the causative agents of greening disease in citrus, an unccurable, devastating disease of citrus worldwide. CLas is vectored byDiaphorina citri, and the understanding of the molecular interplay between vector and pathogen will provide additional basis for the development and implementation of successful management strategies. We focused in the molecular interplay occurring in the gut of the vector, a major barrier for CLas invasion and colonization. We investigated the differential expression of vector and CLas genes by analyzing ade novoreference metatranscriptome of the gut of adult psyllids fed of CLas-infected and healthy citrus plants for 1-2, 3-4 and 5-6 days. CLas regulates the immune response of the vector affecting the production of reactive species of oxygen and nitrogen, and the production of antimicrobial peptides. Moreover, CLas overexpressedperoxiredoxinin a protective manner. The major transcript involved in immune expression was related to melanization, aCLIP-domain serine proteasewe believe participates in the wounding of epithelial cells damaged during infection, which is supported by the down-regulation ofpangolin. We also detected that CLas modulates the gut peristalsis of psyllids through the down-regulation oftitin, reducing the elimination of CLas with faeces. The up-regulation of the neuromodulatorarylalkylamine N-acetyltransferaseimplies CLas also interferes with the double brain-gut communication circuitry of the vector. CLas colonizes the gut by expressing twoType IVb pilin flpgenes and several chaperones that can also function as adhesins. We hypothesized biofil formation occurs by the expression of the cold shock protein of CLas. We also describe the interplay during cell invasion and modification, and propose mechanisms CLas uses to invade the host hemocel. We identified several specific targets for the development of strategies directed to interfere with the successful utilization of the psyllid vector by this pathogen.Author SummaryHuanglongbing (HLB) or greening is an incurable disease causing severe damage to citrus production, making citrus industrial activity unsustainable in several countries around the world. HLB is caused by three species ofCandidatusLiberibacter.Ca.L. asiaticus (CLas), vectored by the psyllidDiaphorina citri, is the prevalent species. Attempts to apply new technologies in the development of strategies for disease and pest management are been made. However, we still miss basic information on this system to efficiently apply the current technologies and envisage the implementation of new approaches for pest control, despite the relevant scientific contribution available. One major gap is regarded to the molecular interplay between CLas and its vector. We focused our attention in the molecular interplay occurring at the first relevant interaction of CLas andD. citri, represented by the gut barrier. We report the transcriptional activity of CLas during the invasion and establishment of the infection in the gut of the vector, as well as the transcriptional activity of the vector in response to the infection. We identified several host genes that are targeted and regulated by CLas as well as several CLas genes that are promising targets for the application of new management strategies.

AbstractAnaplasmosis, caused by infection with bacteria of the genusAnaplasmais an important veterinary and zoonotic disease. The characterization of transmission has concentrated on ticks and little is known about non-tick vectors of livestock anaplasmosis. This study investigated the presence ofAnaplasmaspp. in camels in northern Kenya and whether the hematophagous camel ked,Hippobosca camelina, acts as a vector. Camels (n =976) and > 10,000 keds were sampled over a three-year study period and the presence ofAnaplasmaspecies was determined by PCR-based assays targeting theAnaplasmataceae16S rRNA gene. Camels were infected by‘CandidatusAnaplasma camelii’occurring from 63 - 78% during the dry (September 2017), wet (June-July 2018), and late wet seasons (July-August 2019). 10 - 29% of camel keds harbored ‘Ca. Anaplasma camelii’ acquired from infected camels during blood feeding. We determined whetherAnaplasmapositive camel keds could transmit ‘Ca. Anaplasma camelii’ to small laboratory animals via blood-feeding. We show competence in pathogen transmission and subsequent infection in mice and rabbits by both direct detection in blood smears and subsequent molecular identification by PCR. Transmission of ‘Ca. Anaplasma camelii’ to mice (8 - 47%) and rabbits (25%) occurred readily after ked bites. Hence, we demonstrate, for the first time, the potential ofH. camelinaas a vector of anaplasmosis. This key finding provides the basis for establishing ked control programmes for improvement of livestock and human health.Author summaryHematophagous flies such as Tabanids andStomoxys, among other biting flies, are mechanical transmitters of various pathogens such as African trypanosomes andAnaplasmaspecies. However, little is known about the role of common camel-specific biting keds (also known as camel flies or louse flies, genusHippobosca) in pathogen transmission. Keds inflict painful bites to access host blood, and in the process may transmit bacterial hemopathogens frequently detected in both camels and their keds. We confirmed by experimental blood-feeding, gene amplification, and amplicon sequencing that camel keds can transmit “CandidatusAnaplasma camelii” from naturally-infected camels to healthy mice and rabbits. The high prevalence of camel anaplasmosis throughout the year in northern Kenya could be explained by the infestation camel-specificH. camelina, whose capacity as efficient fliers, unlike ticks, promotes disease transmission and maintenance within and among camel herds. Although this study focused on the transmission ofAnaplasmasp. by camel keds, it is possible that other hemopathogens could also be transmitted by these flies through a similar mechanism. Notably, in the absence of their preferred hosts, keds occasionally bite humans and other vertebrates they come across in order to acquire bloodmeals, and in the process could transmit zoonotic pathogens.

‘Candidatus Liberibacter asiaticus,’ an uncultured α-proteobacterium, is associated with citrus huanglongbing (HLB, yellow shoot disease), a destructive disease threatening citrus production worldwide. Here, we reported the draft genome sequence of ‘Ca. L. asiaticus’ strain Myan16 from an HLB-affected lime tree in Myitkyina, Kachin State, Myanmar. The strain Myan16 genome is 1,229,102 bp with an average G+C content of 36.4%, along with a circular prophage: P-Myan16-2 (36,303 bp, type 2). This is the first genome sequence of a ‘Ca. L. asiaticus’ strain from Myanmar, which will enrich the current ‘Ca. L. asiaticus’ genome sequence database and facilitate HLB epidemiology research in Asia and world.

AbstractNonulosonic acids (NulOs) are a family of acidic carbohydrates with a nine-carbon backbone, which include different related structures, such as sialic acids. They have mainly been studied for their relevance in animal cells and pathogenic bacteria. Recently, sialic acids have been discovered as an important compound in the extracellular matrix of virtually all microbial life and in “CandidatusAccumulibacter phosphatis”, a well-studied polyphosphate-accumulating organism, in particular. Here, bioaggregates highly enriched with these bacteria (approx. 95% based on proteomic data) were used to study the production of NulOs in an enrichment of this microorganism. Fluorescence lectin-binding analysis, enzymatic quantification, and mass spectrometry were used to analyze the different NulOs present, showing a wide distribution and variety of these carbohydrates, such as sialic acids and bacterial NulOs, in the bioaggregates. Phylogenetic analysis confirmed the potential of “Ca. Accumulibacter” to produce different types of NulOs. Proteomic analysis showed the ability of “Ca. Accumulibacter” to reutilize and reincorporate these carbohydrates. This investigation points out the importance of diverse NulOs in non-pathogenic bacteria, which are normally overlooked. Sialic acids and other NulOs should be further investigated for their role in the ecology of “Ca. Accumulibacter” in particular, and biofilms in general.Key Points•“Ca. Accumulibacter” has the potential to produce a range of nonulosonic acids.•Mass spectrometry and lectin binding can reveal the presence and location of nonulosonic acids.•The role of nonulosonic acid in non-pathogenic bacteria needs to be studied in detail.

Melatonin is synthesized from the amino acid L-tryptophan via the shikimic acid pathway and ubiquitously distributed in both prokaryotes and eukaryotes. Although most of melatonin biosynthesis genes were characterized in several plants and animal species including the insect model, Drosophila melanogaster, none of these enzymes have been identified from the Asian citrus psyllid, Diaphorina citri. We used comprehensive in silico analysis and gene expression techniques to identify the melatonin biosynthesis-related genes of D. citri and to evaluate the expression patterns of these genes within the adults of D. citri with gradient infection rates (0, 28, 34, 50, 58, and 70%) of the phytopathogenic bacterium Candidatus Liberibacter asiaticus and after the treatment with exogenous melatonin. We showed that the D. citri genome possesses six putative melatonin biosynthesis-related genes including two putative tryptophan 5-hydroxylase (DcT5H-1 and DcT5H-2), a putative aromatic amino acid decarboxylase (DcAADC), two putative arylalkylamine N-acetyltransferase (DcAANAT-1 and DcAANAT-2), and putative N-acetylserotonin O-methyltransferase (DcASMT). The infection with Ca. L. asiaticus decreased the transcript levels of all predicted genes in the adults of D. citri. Moreover, melatonin supplementation induced their expression levels in both healthy and Ca. L. asiaticus-infected psyllids. These findings confirm the association of these genes with the melatonin biosynthesis pathway.