Publications

4474

Peach orchards in the northeast of Spain were severely affected in 2012 by a previously unreported disease in this area. The symptoms included early reddening, leaf curling, decline, abnormal fruits, and in some cases death of the peach trees. All the infected peach samples were positive for ‘ Candidatus Phytoplasma pyri’, but none were infected by the ‘ Ca . Phytoplasma prunorum’. In this work, potential vectors able to transmit ‘ Ca . Phytoplasma pyri’ from pear to peach and between peach trees were studied and their infective potential was analysed at different times of the year. Transmission trials of the phytoplasma with potential vectors to an artificial feeding medium for insects and to healthy peach trees were conducted. Additionally, isolated phytoplasmas were genetically characterized to determine which isolates were able to infect peach trees. Results showed that the only insect species captured inside peach plots that was a carrier of the ‘ Ca . Phytoplasma pyri’ phytoplasma was Cacopsylla pyri . Other insect species captured and known to be phytoplasma transmitters were present in very low numbers, and were not infected with ‘ Ca . Phytoplasma pyri’ phytoplasma. A total of 1928 individuals of C. pyri were captured in the peach orchards, of which around 49% were phytoplasma carriers. All the peach trees exposed to C. pyri in 2014, and 65% in 2015, were infected by ‘ Ca . Phytoplasma pyri’ 1 year after exposure, showing that this species is able to transmit the phytoplasma to peach. Molecular characterization showed that some genotypes are preferentially determined in peach.

Phytoplasmas of the apple proliferation group cause diseases in various fruit trees, mainly apples, pears and apricots. Immunodominant membrane protein, or ‘Imp’, shows high inter‐ and intraspecies gene variability, and is thus frequently used for population studies in these organisms. In this investigation, a survey was carried out of ‘ Candidatus Phytoplasma pyri’ imp gene diversity in the Czech Republic. In total, 12 imp genotypes that could be clustered into nine groups were identified. Using all publicly available data, 17 distinct imp genotypes (labelled A–K) were defined. Interestingly, genotypes C, H and I were more related to ‘ Ca . Phytoplasma mali’ than to other ‘ Ca . Phytoplasma pyri’ imp genotypes, indicating that some strains may represent a transitional type between the two species. As Imp probably plays an important role in host–pathogen interactions, description of its diversity in ‘ Ca . Phytoplasma pyri’ may help in understanding the epidemiology, symptomatology, and other aspects of pear decline disease. A simple RFLP PCR system is presented for rapid and cost‐effective discrimination of ‘ Ca . Phytoplasma pyri’ imp genotypes.

AbstractThermal ecosystems associated with underground coal combustion sites are rare and less studied than geothermal features. Here we analysed microbial communities of near-surface ground layer and bituminous substance in an open quarry heated by subsurface coal fire by metagenomic DNA sequencing. Taxonomic classification revealed dominance of only a few groups of Firmicutes. Near-complete genomes of three most abundant species, ‘Candidatus Carbobacillus altaicus’ AL32, Brockia lithotrophica AL31, and Hydrogenibacillus schlegelii AL33, were assembled. According to the genomic data, Ca. Carbobacillus altaicus AL32 is an aerobic heterotroph, while B. lithotrophica AL31 is a chemolithotrophic anaerobe assimilating CO2 via the Calvin cycle. H. schlegelii AL33 is an aerobe capable of both growth on organic compounds and carrying out CO2 fixation via the Calvin cycle. Phylogenetic analysis of the large subunit of RuBisCO of B. lithotrophica AL31 and H. schlegelii AL33 showed that it belongs to the type 1-E. All three Firmicutes species can gain energy from aerobic or anaerobic oxidation of molecular hydrogen, produced as a result of underground coal combustion along with other coal gases. We propose that thermophilic Firmicutes, whose spores can spread from their original geothermal habitats over long distances, are the first colonizers of this recently formed thermal ecosystem.