Publications

4466

AbstractBellis perennis virescence (BellVir) phytoplasma affects ornamental daisies in Argentina. It has been previously classified within the X-disease group, subgroup III-J, which is one of the most important and widely distributed in South America, affecting diverse plant hosts. In this study, we compared 16S rRNA, ribosomal proteins rpIV and rps3, secA and immunodominant proteins imp and idpA genes of BellVir phytoplasma with previously described ‘Candidatus Phytoplasma’ species. The 16S rRNA gene of strain BellVir shared less than 97.5% with all previously described ‘Ca. Phytoplasma’ taxa except for ‘Ca. Phytoplasma pruni’. According to the recommended rules for the description of novel taxa within ‘Ca. Phytoplasma’, it should be considered as ‘Ca. P. pruni’-related strain. However, multilocus analysis showed further molecular diversity that distinguished BellVir phytoplasma from ‘Ca. Phytoplasma pruni’. Besides, BellVir phytoplasma and 16SrIII-J related strains have a geographical distribution restricted to South America, where ‘Ca. P.pruni’ has not been detected. Two insect vectors have been reported to transmit 16SrIII-J phytoplasmas, which have not been found to transmit ‘Ca. Phytoplasma pruni’. Having a wide host range, they have not been detected in Prunus persica. Therefore, based on multilocus sequence analyses, specific vector transmission and geographical distribution, we propose the recognition of the novel phytoplasma species ‘Ca. Phytoplasma platensis’, within the X-disease clade, with Bellis perennis virescence phytoplasma as the reference strain.

AbstractOtiorhynchus sulcatus (Fabricius) (Coleoptera: Curculionidae), commonly known as black vine weevil or simply vine weevil, is an important pest of soft fruit and ornamental crops. This species is endemic to temperate areas of Europe but has spread to many other areas over the last century, including North America and Australasia. The ability of vine weevils to adapt to such different environments is difficult to reconcile with the parthenogenetic reproduction strategy, which is likely to underpin a low genetic diversity. It is therefore tempting to hypothesize that weevil adaptation to different environments is mediated, at least partly, by the microbial communities inhabiting these insects. As a first step towards testing this hypothesis we characterized the composition of the bacterial microbiota in weevils from populations feeding on strawberry plants across four geographically separate locations in the UK. We performed 16S rRNA gene Illumina amplicon sequencing, generating 2 882 853 high‐quality reads. Ecological indices, namely Chao1 and Shannon, revealed that the populations used for this study harboured a low diversity and an uneven bacterial microbiota. Furthermore, β‐diversity analysis failed to identify a clear association between microbiota composition and location. Notably, a single operational taxonomic unit phylogenetically related to Candidatus Nardonella accounted for 81% of the total sequencing reads for all tested insects. Our results indicate that vine weevil bacterial microbiota resembles that of other insects as it has low diversity and it is dominated by few taxa. A prediction of this observation is that location per se may not be a determinant of the microbiota inhabiting weevil populations. Rather, other or additional selective pressures, such as the plant species used as a food source, ultimately shape the weevil bacterial microbiota. Our results will serve as a reference framework to investigate other or additional hypotheses aimed at elucidating vine weevil adaptation to its environment.

In 2017, potato tubers suspected of being infected with the bacterium ‘Candidatus Liberibacter solanacearum’ were received from the Animal and Plant Health Inspection Service in the United States. A total of 368 chipping tubers were observed for internal symptoms of zebra chip disease, which is associated with ‘Ca. L. solanacearum’ infection in the United States, Mexico, Central America, and New Zealand. A single tuber sliced at the stem end showed classic zebra chip symptoms of darkened medullary rays, with streaking and necrotic flecking. The symptomatic tuber was confirmed positive for the bacterium by polymerase chain reaction targeting three different ‘Ca. L. solanacearum’ genes. Sequence analysis of these three genes, and subsequent BLAST analysis, identified the pathogen with 99, 98, and 97% identity to ‘Ca. L. solanacearum’ for the 16S ribosomal RNA gene, 50S ribosomal proteins L10/L12 genes, and the outer membrane protein gene, respectively. Sequence analysis did not identify the sample as one of the six known haplotypes of ‘Ca. L. solanacearum,’ indicating that a seventh haplotype of the pathogen was identified. This new haplotype, designated haplotype F, is now the third haplotype of the bacterium that infects Solanum tuberosum in the United States.

“ Candidatus Accumulibacter phosphatis” is widely found in full-scale wastewater treatment plants, where it has been identified as the key organism for biological removal of phosphorus. Since aeration can account for 50% of the energy use during wastewater treatment, microaerobic conditions for wastewater treatment have emerged as a cost-effective alternative to conventional biological nutrient removal processes. Our report provides strong genomics-based evidence not only that “ Ca . Accumulibacter phosphatis” is the main organism contributing to phosphorus removal under microaerobic conditions but also that this organism simultaneously respires nitrate and oxygen in this environment, consequently removing nitrogen and phosphorus from the wastewater. Such activity could be harnessed in innovative designs for cost-effective and energy-efficient optimization of wastewater treatment systems.

The symbiotic N 2 -fixing cyanobacterium UCYN-A, which is closely related to Braarudosphaera bigelowii , and its eukaryotic algal host have been shown to be globally distributed and important in open-ocean N 2 fixation. These unique cyanobacteria have reduced metabolic capabilities, even lacking genes for oxygenic photosynthesis and carbon fixation. Cyanobacteria generally use energy from photosynthesis for nitrogen fixation but require mechanisms for avoiding inactivation of the oxygen-sensitive nitrogenase enzyme by ambient oxygen (O 2 ) or the O 2 evolved through photosynthesis. This study showed that symbiosis between the N 2 -fixing cyanobacterium UCYN-A and its eukaryotic algal host has led to adaptation of its daily gene expression pattern in order to enable daytime aerobic N 2 fixation, which is likely more energetically efficient than fixing N 2 at night, as found in other unicellular marine cyanobacteria.

The microbial rare biosphere represents the largest pool of biodiversity on Earth and constitutes, in sum of all its members, a considerable part of a habitat’s biomass. Dormancy or starvation is typically used to explain the persistence of low-abundance microorganisms in the environment. We show that a low-abundance microorganism can be highly transcriptionally active while remaining in a zero-growth state for at least 7 weeks. Our results provide evidence that this zero growth at a high cellular activity state is driven by maintenance requirements. We show that this is true for a microbial keystone species, in particular a cosmopolitan but permanently low-abundance sulfate-reducing microorganism in wetlands that is involved in counterbalancing greenhouse gas emissions. In summary, our results provide an important step forward in understanding time-resolved activities of rare biosphere members relevant for ecosystem functions.