Publications

3843

Abstract Background Rickettsia spp. are human pathogens that cause a number of diseases and are transmitted by arthropods, such as ixodid ticks. Estonia is one of few regions where the distribution area of two medically important tick species, Ixodes persulcatus and I. ricinus, overlaps. The nidicolous rodent-associated Ixodestrianguliceps has also recently been shown to be present in Estonia. Although no data are available on human disease(s) caused by tick-borne Rickettsia spp. in Estonia, the presence of three Rickettsia species in non-nidicolous ticks has been previously reported. The aim of this study was to detect, identify and partially characterize Rickettsia species in nidicolous and non-nidicolous ticks attached to rodents in Estonia. Results Larvae and nymphs of I.ricinus (n = 1004), I. persulcatus (n = 75) and I.trianguliceps (n = 117), all removed from rodents and shrews caught in different parts of Estonia, were studied for the presence of Rickettsia spp. by nested PCR. Ticks were collected from 314 small animals of five species [Myodes glareolus (bank voles), Apodemus flavicollis (yellow necked mice), A.agrarius (striped field mice), Microtus subterranius (pine voles) and Sorex araneus (common shrews)]. Rickettsial DNA was detected in 8.7% (103/1186) of the studied ticks. In addition to identifying R.helvetica, which had been previously found in questing ticks, we report here the first time that the recently described I.trianguliceps-associated Candidatus Rickettsia uralica has been identified west of the Ural Mountains. Graphical Abstract

Plant diseases caused by vector-borne pathogens are responsible for tremendous losses and threaten some of the most important agricultural crops. A good example is the citrus greening disease, which is caused by bacteria of the genus Liberibacter and is transmitted by psyllids; it has devastated the citrus industry in the United States, China, and Brazil.

Abstract Zebra chip, is a potato disease associated with the bacterium ‘Candidatus Liberibacter solanacearum’ (Lso) and vectored by the potato psyllid, Bactericera cockerelli Šulc. Potato psyllids are native to North America, where four haplotypes have been described. They are able to colonize a wide range of solanaceous species, crops, and weeds. The epidemiology of zebra chip disease is still poorly understood and might involve the different haplotypes of psyllids as well as two haplotypes of Lso. As several perennial weeds have been recognized as potential host for potato psyllids and Lso, a yearly monitoring of several patches of bittersweet nightshade (Solanum dulcamara) and field bindweed (Convolvulus arvensis) located in the potato-growing region of southern Idaho was conducted from 2013 to 2017, to gain insight into psyllid dynamics in non-potato hosts and Lso presence in the fields. Potato psyllids caught on each host were individually tested for Lso, and a subset were haplotyped based on the CO1 gene, along with the haplotyping of Lso in positive samples. On bittersweet nightshade, the Northwestern haplotype was numerically dominant, with around 2.7% of psyllids found to be carrying either Lso haplotype A or B, suggesting a limited role in zebra chip persistence, which has infected Idaho fields at a low occurrence since the 2012 outbreak. Field bindweed was found to be a transient, non-overwintering host for potato psyllid of Northwestern, Western and Central haplotypes late in the season, suggesting minor, if any, role in persistence of Lso and field infestation by potato psyllids.

“Candidatus Nitrosocaldaceae” are globally distributed in neutral or slightly alkaline hot springs and geothermally heated soils. Despite their essential role in the nitrogen cycle in high-temperature ecosystems, they remain poorly understood because they have never been isolated in pure culture, and very few genomes are available. In the present study, a metagenomics approach was employed to obtain “Ca. Nitrosocaldaceae” metagenomic-assembled genomes (MAGs) from hot spring samples collected from India and China. Phylogenomic analysis placed these MAGs within “Ca. Nitrosocaldaceae.” Average nucleotide identity and average amino acid identity analysis suggested the new MAGs represent two novel species of “Candidatus Nitrosocaldus” and a novel genus, herein proposed as “Candidatus Nitrosothermus.” Key genes responsible for chemolithotrophic ammonia oxidation and a thaumarchaeal 3HP/4HB cycle were detected in all MAGs. Furthermore, genes coding for urea degradation were only present in “Ca. Nitrosocaldus,” while biosynthesis of the vitamins, biotin, cobalamin, and riboflavin were detected in almost all MAGs. Comparison of “Ca. Nitrosocaldales/Nitrosocaldaceae” with other AOA revealed 526 specific orthogroups. This included genes related to thermal adaptation (cyclic 2,3-diphosphoglycerate, and S-adenosylmethionine decarboxylase), indicating their importance for life at high temperature. In addition, these MAGs acquired genes from members from archaea (Crenarchaeota) and bacteria (Firmicutes), mainly involved in metabolism and stress responses, which might play a role to allow this group to adapt to thermal habitats.

Huanglongbing (HLB) is the most destructive, yet incurable disease of citrus. Finding sources of genetic resistance to HLB-associated ‘Candidatus Liberibacter asiaticus’ (Las) becomes strategic to warrant crop sustainability, but no resistant Citrus genotypes exist. Some Citrus relatives of the family Rutaceae, subfamily Aurantioideae, were described as full-resistant to Las, but they are phylogenetically far, thus incompatible with Citrus. Partial resistance was indicated for certain cross-compatible types. Moreover, other genotypes from subtribe Citrinae, sexually incompatible but graft-compatible with Citrus, may provide new rootstocks able to restrict bacterial titer in the canopy. Use of seedlings from monoembryonic species and inconsistencies in previous reports likely due to Las recalcitrance encouraged us to evaluate more accurately these Citrus relatives. We tested for Las resistance a diverse collection of graft-compatible Citrinae species using an aggressive and consistent challenge-inoculation and evaluation procedure. Most Citrinae species examined were either susceptible or partially resistant to Las. However, Eremocitrus glauca and Papua/New Guinea Microcitrus species as well as their hybrids and those with Citrus arose here for the first time as full-resistant, opening the way for using these underutilized genotypes as Las resistance sources in breeding programs or attempting using them directly as possible new Las-resistant Citrus rootstocks or interstocks.

Abstract BACKGROUND: Rickettsia spp. are human pathogens that cause a number of diseases and are transmitted by arthropods, such as ixodid ticks. Estonia is one of few regions where the distribution area of two medically important tick species, Ixodes persulcatus and I. ricinus, overlaps. The presence of the nidicolous rodent-associated I. trianguliceps has also recently been shown in Estonia. Although there is no data available in Estonia on human disease caused by tick-borne Rickettsia spp., the presence of three Rickettsia species in non-nidicolous ticks was also previously reported. The aim of this study was to detect, identify and partially characterize Rickettsia species in nidicolous and non-nidicolous ticks attached to rodents.RESULTS: Larvae and nymphs of I. ricinus (n = 1004), I. persulcatus (n = 75) and I. trianguliceps (n = 117) removed from rodents and shrews caught in different parts of Estonia were studied for the presence of Rickettsia spp. by nested PCR. Ticks were collected from 314 small animals of 5 species (Myodes glareolus (bank voles), Apodemus flavicollis (yellow necked mice), A. agrarius (striped field mice), Microtus subterranius (pine voles) and Sorex araneus (common shrews)). Rickettsial DNA was detected in 8.7% (103/1186) of the studied ticks. In addition to R. helvetica previously found in questing ticks, this study reports the first identification of the recently described I. trianguliceps-associated Candidatus R. uralica west of the Ural Mountains.

The farnesyltransferase α-subunit (FTA) may be involved in the regulation of defence responses against pathogens in plants. In this study, this gene was amplified from Catharanthus roseus (CrFTA gene). The cDNA was found to be 1 403 bp long, and encodes a putative protein of 331 amino acids that contains a conserved PPTA motif. The phylogenetic analysis showed that the sequence of CrFTA is the most similar to that from Coffea canephora. The qRT-PCR assays indicated that CrFTA is expressed in the leaves, stems, and roots. During a Candidatus Liberibacter asiaticus (Ca. L. asiaticus) infection, the CrFTA expression levels significantly increased and reached 18-fold that measured in the control group, after which its expression decreased gradually from 22 days after top-grafting (DAT) to the end of the experiment. Spray application of Manumycin A (ManuA), a specific inhibitor of farnesyltransferase, on the leaves of C. roseus plants caused a significant decrease in the CrFTA expression and a significant increase in the Ca. L. asiaticus positivity percentage after top-grafting with the Ca. L. asiaticus-infected shoots compared with the groups not treated with ManuA. Furthermore, ABA had no significant effect on the relative expression of CrFTA and the number of Ca. L. asiaticus-positive plants. These results suggest that CrFTA most likely plays a role in mediating the tolerance to a Ca. L. asiaticus infection in C. roseus.

AbstractCitrus Greening disease (CG) in South Africa (SA) is associated with the fastidious bacterium ‘Candidatus Liberibacter africanus’ (Laf). It has been observed that Laf isolates obtained from different geographic localities in SA differed in the rate of transmission during grafting experiments leading to the hypothesis that genetic variation of Laf may exist in this country. To determine this, 167 Laf isolates obtained from Limpopo, North West, Mpumalanga and the Western Cape were subjected to microsatellite analyses, using four polymorphic markers. From UPGMA and STRUCTURE analysis, it was shown that most sources belong to one of two major genetic groups of Laf and these comprise 25 distinct haplotypes. Four samples included within this study did not group with these two major groups, suggesting a potential third and fourth genetic group of Laf being present, which can be validated by further sampling. Results further indicate that Laf populations in SA are formed by geographic locality. The high genetic diversity observed for Laf within this study is consistent with the hypothesis that Laf originated on the African continent, warranting further genetic analysis of Laf populations from Africa. This is the first study to unveil the genetic diversity of Laf.