Publications

4788

Long-term sustainable management of zebra chip (ZC) disease of potato requires development of tolerant or resistant germplasm. To this end, 283 potato varieties and breeding clones were infected with the ZC putative causal agent ‘Candidatus Liberibacter solanacearum’ (Lso) by potato psyllid vector inoculations in 2010, 2011, 2012, and 2013. Potato germplasm was then examined for development of fresh and fried ZC symptoms. Over multiple years 29 breeding clones exhibited little to no symptoms in freshly cut tuber slices, and five exhibited little to no symptoms in fried slices. These five presumed tolerant breeding clones were chosen for further screening to determine whether the lack of physiological responses to Lso infection was the cause of observed tolerance. To this end, tuber amino acid, sugar, and phenolic levels were compared between noninfected and Lso-infected plants. The five putative tolerant clones had less dramatic shifts in host physiology following Lso infection than the susceptible Atlantic cultivar. This suggested lack of host responses to Lso infection that result in major changes in tuber biochemistry is a potential mechanism of ZC resistance. However, the susceptible Atlantic cultivar did have consistently greater Lso titers compared with two of the tolerant entries, so for these reductions in Lso pathogen progression also might be a factor. Regardless, lack of host responses could still remain one trait that could be used to aid in selection of ZC-resistant potato varieties, as other tolerant lines had infection levels consistent with susceptible Atlantic cultivar. These results also suggest that germplasm derived from relatives of cultivated potato plants are viable sources of ZC disease resistance.

To improve the knowledge base of Borrelia in north Africa, we tested 257 blood samples collected from febrile patients in Oran, Algeria, between January and December 2012 for Borrelia species using flagellin gene polymerase chain reaction sequencing. A sequence indicative of a new Borrelia sp. named Candidatus Borrelia algerica was detected in one blood sample. Further multispacer sequence typing indicated this Borrelia sp. had 97% similarity with Borrelia crocidurae, Borrelia duttonii, and Borrelia recurrentis. In silico comparison of Candidatus B. algerica spacer sequences with those of Borrelia hispanica and Borrelia garinii revealed 94% and 89% similarity, respectively. Candidatus B. algerica is a new relapsing fever Borrelia sp. detected in Oran. Further studies may help predict its epidemiological importance.

‘Candidatus Phytoplasma cynodontis’ is widespread in bermudagrass and has only been found in monocotyledonous plants. Molecular studies carried out on strains collected in Italy, Serbia, and Albania enabled verification of molecular variability in the 16S ribosomal RNA (rRNA) gene. Based on restriction fragment length polymorphism and sequence analyses, the strains from Serbia were clearly differentiated from all others and assigned to a new ribosomal DNA (rDNA) subgroup designated as 16SrXIV-C. A system for amplification of fragments containing the ‘Ca. P. cynodontis’ groEL gene was developed to enable study of its variability in related strains belonging to different 16SrXIV subgroups. Despite the fact that the groEL gene exhibited a greater sequence variation than 16S rRNA, the phylogenetic tree based on groEL gene sequence analysis was highly congruent with the 16S rDNA-based tree. The groEL gene analyses supported differentiation of the Serbian strains and definition of the new subgroup 16SrXIV-C. Phylogenetic analyses of both genes confirmed distinct phylogenetic lineages for strains belonging to 16SrXIV subgroups. Furthermore, groEL is the only nonribosomal marker developed for characterization of ‘Ca. P. cynodontis’ thus far, and its application in molecular surveys should provide better insight into the relationships among these phytoplasmas and correlation between strain differentiation and their geographical distribution.

Abstract Methylotrophic planktonic bacteria fulfill a particular role in the carbon cycle of lakes via the turnover of single-carbon compounds. We studied two planktonic freshwater lineages (LD28 and PRD01a001B) affiliated with Methylophilaceae (Betaproteobacteria) in Lake Zurich, Switzerland, by a combination of molecular and cultivation-based approaches. Their spatio-temporal distribution was monitored at high resolution (n=992 samples) for 4 consecutive years. LD28 methylotrophs constituted up to 11 × 107 cells l−1 with pronounced peaks in spring and autumn–winter, concomitant with blooms of primary producers. They were rare in the warm water layers during summer but abundant in the cold hypolimnion, hinting at psychrophilic growth. Members of the PRD01a001B lineage were generally less abundant but also had maxima in spring. More than 120 axenic strains from these so far uncultivated lineages were isolated from the pelagic zone by dilution to extinction. Phylogenetic analysis separated isolates into two distinct genotypes. Isolates grew slowly (μmax=0.4 d−1), were of conspicuously small size, and were indeed psychrophilic, with higher growth yield at low temperatures. Growth was enhanced upon addition of methanol and methylamine to sterile lake water. Genomic analyses of two strains confirmed a methylotrophic lifestyle with a reduced set of genes involved in C1 metabolism. The very small and streamlined genomes (1.36 and 1.75 Mb) shared several pathways with the marine OM43 lineage. As the closest described taxa (Methylotenera sp.) are only distantly related to either set of isolates, we propose a new genus with two species, that is, ‘Candidatus Methylopumilus planktonicus’ (LD28) and ‘Candidatus Methylopumilus turicensis’ (PRD01a001B).