Publications

4527

AbstractThe Yessentukskoye deposit of Caucasian mineral waters contains balneologically valuable drinking mineral water, which is extracted from the Upper Cretaceous 1 km subsurface aquifer and is almost unexplored by microbiologists. We have sampled this water via continuously operating production wells, characterized the phylogenetic diversity of its microbial community, and obtained enrichments of thermophilic iron reducers from the source aquifer. From the enrichments, a novel anaerobic thermophilic bacterium, reducing Fe(III) in the mineral ferrihydrite with acetate as the electron donor, was isolated into a pure culture. The novel isolate, designated as strain Es71-Z0220Tbelonging toDeferribacteralesorder, is thermophilic, neutrophilic, halotolerant, motile vibrio. It utilizes synthesized ferrihydrite, fumarate, nitrate or elemental sulfur as the electron acceptors with organic acids as the electron donors. The strain is incapable of soluble Fe(III) complexes reduction and fermentative growth. The draft genome assembly of strain Es71-Z0220Tresulted in 65 contigs with a total size of ca. 2.3 Mb. On the basis of whole-genome phylogenetic reconstruction and physiological characterization, the novel isolate was considered to represent a novel family, genus and species for which the nameDeferrivibrio essentukiensisgen. nov., sp. nov. is proposed. Genome analysis revealed key determinants of anaerobic respiration and carbon substrate utilization pathways in the organism with peculiarities related to putative Fe(III)-reducing electron transfer chain. Considering the revealed metabolic features ofDeferrivibrio essentukiensis, the involvement of the organism in its subsurface environment in biogeochemical by carbon cycling by coupling the organic matter oxidation with Fe(III) minerals reduction is discussed.

Summary Huanglongbing (HLB) is currently considered the most destructive disease of citrus worldwide. In the major citrus‐growing areas in Asia and the US, the major causal agent of HLB is the bacterial pathogen Candidatus Liberibacter asiaticus (CLas). CLas is vectored by the Asian citrus psyllid, Diaphorina citri , in a persistent propagative manner. CLas cannot be cultured in vitro because of its unclear growth factors, leading to uncertainty in the infection mechanism of CLas at the cellular level in citrus and in D. citri . To characterize the detailed infection of CLas in the host and vector, the incidence of HLB was first investigated in citrus‐growing fields in Fujian Province, China. It was found that the positive association of the level of CLas infection in the leaves correlated with the symptoms. Then antibodies against peptides of the outer membrane protein (OMP) of CLas were prepared and tested. The antibodies OMP‐225, OMP‐333 and OMP724 showed specificity to citrus plants in western blot analyses, whereas the antibodies OMP‐47 and OMP‐225 displayed specificity to the D. citri vector. The application of OMP‐225 in the immunofluorescence assay indicated that CLas was located in and distributed throughout the phloem sieve cells of the leaf midribs and axile placenta of the fruit. CLas also infected the epithelial cells and visceral muscles of the alimentary canal of D. citri . The application of OMP‐333 in immunoelectron microscopy indicated the round or oval CLas in the sieve cells of leaf midribs and axile placenta of fruit as well as in the epithelial cells and reticular tissue of D. citri alimentary canal. These results provide a reliable means for HLB detection, and enlighten a strategy via neutralizing OMP to control HLB. These findings also provide insight for the further investigation on CLas infection and pathogenesis, as well as CLas–vector interaction.

AbstractPeach trees showing witches’‐broom disease symptoms in the northwest of Iran were sampled for phytoplasma detection. PCR assays and Sanger sequence analyses indicated that ʻCandidatus Phytoplasma phoeniciumʼ was associated with peach witchesʼ‐broom disease. Virtual RFLP analyses of the 16S rRNA gene indicated that ʻCa. Phytoplasma phoeniciumʼ strain, which was prevalent in the northwest of Iran belonged to 16SrIX‐C subgroup. For the genomic characterization of Iranian ʻCa. Phytoplasma phoeniciumʼ strain, total DNA extracted from the infected peach trees was subjected to Illumina next‐generation sequencing. The NGS sequencing resulted in 41157647 read pairs of raw data. The raw reads length was 150 bp and the insert size was 350 bp. Assembly and genes clustering finally resulted in 750 contigs with a total size of 228345 bp. The GC content of sequence was 33.2%, N50 value was 259 and L50 value was 256. According to NCBI‐ PGAP annotation the genome of Prunus persica phytoplasma PP2 contained 410 genes including 377 CDSs with protein, 10 rRNAs, nine tRNAs and 14 pseudogenes.

Summary Complete genomes can be recovered from metagenomes by assembling and binning DNA sequences into metagenome assembled genomes (MAGs). Yet, the presence of microdiversity can hamper the assembly and binning processes, possibly yielding chimeric, highly fragmented and incomplete genomes. Here, the metagenomes of four samples of aerobic granular sludge bioreactors containing Candidatus ( Ca .) Accumulibacter, a phosphate‐accumulating organism of interest for wastewater treatment, were sequenced with both PacBio and Illumina. Different strategies of genome assembly and binning were investigated, including published protocols and a binning procedure adapted to the binning of long contigs (MuLoBiSC). Multiple criteria were considered to select the best strategy for Ca . Accumulibacter, whose multiple strains in every sample represent a challenging microdiversity. In this case, the best strategy relies on long‐read only assembly and a custom binning procedure including MuLoBiSC in metaWRAP. Several high‐quality Ca . Accumulibacter MAGs, including a novel species, were obtained independently from different samples. Comparative genomic analysis showed that MAGs retrieved in different samples harbour genomic rearrangements in addition to accumulation of point mutations. The microdiversity of Ca . Accumulibacter, likely driven by mobile genetic elements, causes major difficulties in recovering MAGs, but it is also a hallmark of the panmictic lifestyle of these bacteria.

AbstractPear decline, induced by the phytoplasma 'CandidatusPhytoplasma pyri', transmitted by pear psyllids, is one of the most devastating diseases onPyrus communisin Europe and North America. Investigations of pear psyllids in 4 pear orchards in lower Austria showed the presence ofCacopsylla pyri,C. pyricolaandC. pyrisugaat all locations. PCR analyses revealed overall phytoplasma infection rates forC. pyriof 5.4%, forC. pyricola,of 4.6%, forC. pyrisugaremigrants of 9.6% and forC. pyrisugaemigrants of 0%. The rates of PCR-positiveC. pyriandC. pyricolaindividuals varied greatly in the course of the year, and the highest infection rates were observed in late summer, autumn and in late winter. In transmission experiments with healthy pear seedlings, winterform individuals ofC. pyri and C. pyricolatransmitted the pathogen to 19.2% (5 out of 26) and 4.8% (2 out of 41) of the test plants, respectively. The vectoring ability ofC. pyrisugawas experimentally proven for the first time, and in transmission experiments with remigrants, 9.5% (2 out of 21) of the pear seedlings were infected. Our data indicate a significant risk of pathogen transmission in pear orchards during the greater part of the year, especially in late winter, early spring and autumn. Multilocus sequence analysis by aid of the genesaceFandimpallowed the discrimination between 15 phytoplasma types. Three so far undescribedaceFgenotypes and four undescribedimpgenotypes were identified.

Abstract Background The tomato psyllid, Bactericera cockerelli Šulc (Hemiptera: Triozidae), is a pest of solanaceous crops such as tomato (Solanum lycopersicum L.) in the U.S. and vectors the disease-causing pathogen ‘Candidatus Liberibacter solanacearum’ (or Lso). Disease symptom severity is dependent on Lso haplotype: tomato plants infected with Lso haplotype B experience more severe symptoms and higher mortality compared to plants infected with Lso haplotype A. By characterizing the molecular differences in the tomato plant’s responses to Lso haplotypes, the key components of LsoB virulence can be identified and, thus, targeted for disease mitigation strategies. Results To characterize the tomato plant genes putatively involved in the differential immune responses to Lso haplotypes A and B, RNA was extracted from tomato ‘Moneymaker’ leaves 3 weeks after psyllid infestation. Gene expression levels were compared between uninfected tomato plants (i.e., controls and plants infested with Lso-free psyllids) and infected plants (i.e., plants infested with psyllids infected with either Lso haplotype A or Lso haplotype B). Furthermore, expression levels were compared between plants infected with Lso haplotype A and plants infected with Lso haplotype B. A whole transcriptome analysis identified 578 differentially expressed genes (DEGs) between uninfected and infected plants as well as 451 DEGs between LsoA- and LsoB-infected plants. These DEGs were primarily associated with plant defense against abiotic and biotic stressors, growth/development, plant primary metabolism, transport and signaling, and transcription/translation. These gene expression changes suggested that tomato plants traded off plant growth and homeostasis for improved defense against pathogens, especially when infected with LsoB. Consistent with these results, tomato plant growth experiments determined that LsoB-infected plants were significantly stunted and had impaired negative geotropism. However, it appeared that the defense responses mounted by tomatoes were insufficient for overcoming the disease symptoms and mortality caused by LsoB infection, while these defenses could compensate for LsoA infection. Conclusion The transcriptomic analysis and growth experiments demonstrated that Lso-infected tomato plants underwent gene expression changes related to abiotic and biotic stressors, impaired growth/development, impaired plant primary metabolism, impaired transport and signaling transduction, and impaired transcription/translation. Furthermore, the transcriptomic analysis also showed that LsoB-infected plants, relative to LsoA-infected, experienced more severe stunting, had improved responses to some stressors and impaired responses to others, had poorer transport and signaling transduction, and had impaired carbohydrate synthesis and photosynthesis.