Publications

4495

The close association between the olive flyBactrocera oleae(Rossi) (Diptera: Tephritidae) and bacteria has been known for more than a century. Recently, the presence of a host-specific, hereditary, unculturable symbiotic bacterium, designated ‘CandidatusErwinia dacicola’, has been described inside the cephalic organ of the fly, called the oesophageal bulb. In the present study, the 16S rRNA gene sequence variability of ‘Ca.E. dacicola’ was examined within and between 26 Italian olive fly populations sampled across areas where olive trees occur in the wild and areas where cultivated olive trees have been introduced through history. The bacterial contents of the oesophageal bulbs of 314 olive flies were analysed and a minimum of 781 bp of the 16S rRNA gene was sequenced. The corresponding host fly genotype was assessed by sequencing a 776 bp portion of the mitochondrial genome. Two ‘Ca. E. dacicola’ haplotypes were found (htA and htB), one being slightly more prevalent than the other (57 %). The two haplotypes did not co-exist in the same individuals, as confirmed by cloning. Interestingly, the olive fly populations of the two main Italian islands, Sicily and Sardinia, appeared to be represented exclusively by the htB and htA haplotypes, respectively, while peninsular populations showed both bacterial haplotypes in different proportions. No significant correlation emerged between the two symbiont haplotypes and the 16 host fly haplotypes observed, suggesting evidence for a mixed model of vertical and horizontal transmission of the symbiont during the fly life cycle.

Temperature has been shown to have a significant effect on development of liberibacter species associated with citrus Huanglongbing disease. ‘Candidatus Liberibacter africanus’ and ‘Ca. L. americanus’ are both heat sensitive, whereas ‘Ca. L. asiaticus’ is heat tolerant. The recently described ‘Ca. L. solanacearum’ is associated with zebra chip (ZC), a newly emerging and economically important disease of potato worldwide. This psyllid-transmitted liberibacter species severely affects several other solanaceous crops and carrot. Experiments were conducted to evaluate effects of temperature on development of ‘Ca. L. solanacearum’ and ZC disease. Potato plants were inoculated with ‘Ca. L. solanacearum’ by briefly exposing them to liberibacter-infective potato psyllids at various temperatures under laboratory conditions. Following insect exposure, the plants were maintained at selected temperature regimes in growth chambers, monitored for ZC symptom development, and later tested for liberibacter by polymerase chain reaction to confirm infection. Results indicated that temperatures below 17°C appear to slow development of ‘Ca. L. solanacearum’ and ZC symptoms, whereas temperatures above 32°C are detrimental to this liberibacter. Compared to Huanglongbing liberibacters, ‘Ca. L. solanacearum’ appears heat sensitive. The sensitivity of this bacterium and its insect vector to temperature may partially explain incidence, severity, and distribution of ZC in affected regions.

Summary Candidatus Chloracidobacterium thermophilum, which naturally inhabits microbial mats of alkaline siliceous hot springs in Yellowstone National Park, is the only known chlorophototroph in the phylum Acidobacteria . The Ca . C .  thermophilum genome was composed of two chromosomes (2 683 362 bp and 1 012 010 bp), and both encoded essential genes. The genome included genes to produce chlorosomes, the Fenna‐Matthews‐Olson protein, bacteriochlorophylls a and c as principal pigments, and type‐1, homodimeric reaction centres. Ca . C. thermophilum is an aerobic photoheterotroph that lacks the ability to synthesize several essential nutrients. Key genes of all known carbon fixation pathways were absent, as were genes for assimilatory nitrate and sulfate reduction and vitamin B 12 synthesis. Genes for the synthesis of branched‐chain amino acids (valine, isoleucine and leucine) were also absent, but genes for catabolism of these compounds were present. This observation suggested that Ca . C. thermophilum may synthesize branched‐chain amino acids from an intermediate(s) of the catabolic pathway by reversing these reactions. The genome encoded an aerobic respiratory electron transport chain that included NADH dehydrogenase, alternative complex III and cytochrome oxidase. The chromosomes of the laboratory isolate were compared with assembled, metagenomic scaffolds from the major Ca . C. thermophilum population in hot‐spring mats. The larger chromosomes of the two populations were highly syntenous but significantly divergent (∼13%) in sequence. In contrast, the smaller chromosomes have undergone numerous rearrangements, contained many transposases, and might be less constrained by purifying selection than the large chromosomes. Some transposases were homologous to those of mat community members from other phyla.

ABSTRACT Members of the noncultured clade of Frankia enter into root nodule symbioses with actinorhizal species from the orders Cucurbitales and Rosales. We report the genome sequence of a member of this clade originally from Pakistan but obtained from root nodules of the American plant Datisca glomerata without isolation in culture.

Summary In this study, members of a specific group of thin (6–14 µm filament diameter), vacuolated Beggiatoa‐ like filaments from six different hypersaline microbial mats were morphologically and phylogenetically characterized. Therefore, enrichment cultures were established, filaments were stained with fluorochromes to show intracellular structures and 16S rRNA genes were sequenced. Morphological characteristics of Beggiatoa‐ like filaments, in particular the presence of intracellular vacuoles, and the distribution of nucleic acids were visualized. In the intracellular vacuole nitrate reached concentrations of up to 650 mM. Fifteen of the retrieved 16S rRNA gene sequences formed a monophyletic cluster and were phylogenetically closely related (≥ 94.4% sequence identity). Sequences of known filamentous sulfide‐oxidizing genera Beggiatoa and Thioploca that comprise non‐vacuolated and vacuolated filaments from diverse habitats clearly delineated from this cluster. The novel monophyletic cluster was furthermore divided into two sub‐clusters: one contained sequences originating from Guerrero Negro (Mexico) microbial mats and the other comprised sequences from five distinct Spanish hypersaline microbial mats from Ibiza, Formentera and Lake Chiprana. Our data suggest that Beggiatoa ‐like filaments from hypersaline environments displaying a thin filament diameter contain nitrate‐storing vacuoles and are phylogenetically separate from known Beggiatoa . Therefore, we propose a novel genus for these organisms, which we suggest to name ‘ Candidatus Allobeggiatoa’.

AbstractWe report the detection of phytoplasmas in Picea abies, Picea glauca and Picea pungens trees with witches’ brooms and other growth abnormalities and also in symptomless trees. Phytoplasmas were detected in c. 25% of the tested plants by polymerase chain reaction using phytoplasma universal P1/P7 followed by R16F2n/R16R2 primer pairs. The phytoplasmas were classified as members of the phylogenetic groups: 16SrI, ‘Ca. Phytoplasma asteris’; 16SrIII, X‐disease phytoplasma group; and 16SrXXI, ‘Ca. Phytoplasma pini’.