Publications

4364

Bacteria that directly use electrodes as metabolic electron donors (biocathodes) have been proposed for applications ranging from microbial electrosynthesis to advanced bioelectronics for cellular communication with machines. However, just as we understand very little about oxidation of analogous natural insoluble electron donors, such as iron oxide, the organisms and extracellular electron transfer (EET) pathways underlying the electrode-cell direct electron transfer processes are almost completely unknown. Biocathodes are a stable biofilm cultivation platform to interrogate both the rate and mechanism of EET using electrochemistry and to study the electroautotrophic organisms that catalyze these reactions. Here we provide new evidence supporting the hypothesis that the uncultured bacterium “CandidatusTenderia electrophaga” directly couples extracellular electron transfer to CO2fixation. Our results provide insight into developing biocathode technology, such as microbial electrosynthesis, as well as advancing our understanding of chemolithoautotrophy.

Abstract‘Candidatus Liberibacter asiaticus’ (CaLas), associated with citrus Huanglongbing (HLB), is a non culturable member of the α-proteobacteria. In this study serologically based methods for the detection of CaLas were developed. An anti-outer membrane protein A (OmpA) polyclonal antibody previously produced (in our laboratory) was highly effective for the detection of CaLas from citrus tissues in a simple tissue printing format. The antibody was also used to capture bacteria from periwinkle extracts. About 80% of all field samples analyzed tested positive with both immune tissue printing and qPCR; whereas 95% were positive with at least one of these two methods. When asymptomatic citrus tissues were tested, the tissue printing method gave a higher rate of detection (83%) than the qPCR method (64%). This is consistent with a lower concentration of CaLas DNA, but a higher proportion of viable cells, in the asymptomatic tissues. The immune tissue printing method also highlights the detail of the spatial distribution of ‘Ca. Liberibacter asiaticus’ in diseased citrus tissues. Both the immune capture PCR and immune tissue printing methods offer the advantages of low cost, high throughput, ease of scaling for multiple samples and simplicity over current PCR-based methods for the detection of ‘Ca. Liberibacter asiaticus’.

It is generally accepted that diverse, poorly characterized microorganisms reside deep within Earth’s crust. One such lineage of deep subsurface-dwelling bacteria is an uncultivated member of the Firmicutes phylum that can dominate molecular surveys from both marine and continental rock fracture fluids, sometimes forming the sole member of a single-species microbiome. Here, we reconstructed a genome from basalt-hosted fluids of the deep subseafloor along the eastern Juan de Fuca Ridge flank and used a phylogenomic analysis to show that, despite vast differences in geographic origin and habitat, it forms a monophyletic clade with the terrestrial deep subsurface genome of “Candidatus Desulforudis audaxviator” MP104C. While a limited number of differences were observed between the marine genome of “Candidatus Desulfopertinax cowenii” modA32 and its terrestrial relative that may be of potential adaptive importance, here it is revealed that the two are remarkably similar thermophiles possessing the genetic capacity for motility, sporulation, hydrogenotrophy, chemoorganotrophy, dissimilatory sulfate reduction, and the ability to fix inorganic carbon via the Wood-Ljungdahl pathway for chemoautotrophic growth. Our results provide insights into the genetic repertoire within marine and terrestrial members of a bacterial lineage that is widespread in the global deep subsurface biosphere, and provides a natural means to investigate adaptations specific to these two environments.

AbstractCandidatus Liberibacter solanacearum (Lso) is bacterium transmitted by psyllids to Solanaceae and Apiaceae plants. So far, Lso is found in Europe affecting Apiaceae. In the Mediterranean region, Bactericera trigonica is the only known vector of Lso, but the leek-onion psyllid Bactericera tremblayi is another widespread psyllid and potential vector of Lso. Commonly, carrot, leek and potato are cultivated in the same zones and it is uncertain if these psyllid species are able to transmit Lso to potato plants. Here, we assessed the transmission of Lso by B. trigonica and B. tremblayi to potato plants. B. trigonica showed preference to ingest from the phloem, settle and oviposit on carrot and celery but not on potato. This was correlated with high Lso transmission rates to both carrot (80%) and celery (70%) but very low to potato (≤3%). B. tremblayi preferred leek over carrot and potato, the latter being the less preferred host. B. tremblayi readily ingested from the phloem of infected carrots but failed to transmit Lso from carrot to carrot. Our study shows that the risk of Lso transmission from Apiaceae to potato by B. trigonica is very low, and that B. tremblayi is not a likely vector of Lso.

Recently, a novel species of the genusBorreliawas identified inBothriocroton concolorandIxodes holocyclusticks from echidnas. Analyses of 16S rRNA andflaBgenes identified three closely related genotypes of this bacterium (Borreliasp. Aus A-C) that were unique and distinct from previously described borreliae. Phylogenetic analyses offlaB(763 bp),groEL(1537 bp),gyrB(1702 bp) andglpQ(874 bp) gene sequences and concatenated sequences (3585 bp) of three gene loci (16S rRNA,flaBandgyrB) were consistent with previous findings and confirm that this novel species of the genusBorreliais more closely related to, yet distinct from, the Reptile-associated (REP) and Relapsing Fever (RF) groups. At theflaBlocus, genotypes A, B and C shared the highest percentage sequence similarities (87.9, 88 and 87.9 %, respectively) withB.orrelia turcica(REP), whereas at thegroELandgyrBloci, these genotypes were most similar (88.2–89.4 %) toB.orrelia hermsii(RF). At theglpQlocus, genotypes A and B were most similar (85.7 and 85.4 % respectively) toBorreliasp. Tortoise14H1 (REP). The presence of theglpQgene, which is absent in the Lyme Borreliosis group spirochaetes, further emphasises that the novel species of the genusBorreliacharacterized in the present study does not belong to this group. Phylogenetic analyses at multiple loci produced consistent topographies revealing the monophyletic grouping of this bacterium, therefore providing strong support for its species status. We propose the name ‘CandidatusBorreliatachyglossi’, and hypothesize that this species of the genusBorreliamay be endemic to Australia. The pathogenic potential of this bacterium is not yet known.