Publications

4618

AbstractBackgroundCitrushuanglongbing(HLB) disease is caused by endogenous, phloem-restricted, Gram negative, uncultured bacteria namedCandidatusLiberibacter africanus (CaLaf),Ca.L. asiaticus (CaLas), andCa.L. americanus (CaLam), depending on the continent where the bacteria were first detected. The Asian citrus psyllid vector,Diaphorina citri, transmits CaLas and CaLam and both Liberibacter species are present in Brazil. Several studies of the transcriptional response of citrus plants manifesting HLB symptoms have been reported, but only for CaLas infection. This study evaluated the transcriptional reprogramming of a susceptible genotype of sweet orange challenged with CaLam, using a customized 385K microarray containing approximately 32,000 unigene transcripts. We analyzed global changes in gene expression of CaLam-infected leaves of sweet orange during the symptomatic stage of infection and compared the results with previously published microarray studies that used CaLas-infected plants. Twenty candidate genes were selected to validate the expression profiles in symptomatic and asymptomatic PCR-positive leaves infected with CaLas or CaLam.ResultsThe microarray analysis identified 633 differentially expressed genes during the symptomatic stage of CaLam infection. Among them, 418 (66%) were upregulated and 215 (34%) were down regulated. Five hundred and fourteen genes (81%) were orthologs of genes fromArabidopsis thaliana. Gene set enrichment analysis (GSEA) revealed that several of the transcripts encoded transporters associated with the endomembrane system, especially zinc transport. Among the most biologically relevant gene transcripts in GSEA were those related to signaling, metabolism and/or stimulus to hormones, genes responding to stress and pathogenesis, biosynthesis of secondary metabolites, oxidative stress and transcription factors belonging to different families. Real time PCR of 20 candidate genes validated the expression pattern of some genes in symptomatic and asymptomatic leaves infected with CaLam or CaLas.ConclusionsMany gene transcripts and biological processes are significantly altered upon CaLam infection. Some of them had been identified in response to CaLas infection, while others had not been previously reported. These data will be useful for selecting target genes for genetic engineering to control HLB.

Abstract Members of the genus Candidatus Accumulibacter are important in many wastewater treatment systems performing enhanced biological phosphorus removal (EBPR). The Accumulibacter lineage can be subdivided phylogenetically into multiple clades, and previous work showed that these clades are ecologically distinct. The complete genome of Candidatus Accumulibacter phosphatis strain UW-1, a member of Clade IIA, was previously sequenced. Here, we report a draft genome sequence of Candidatus Accumulibacter spp. strain UW-2, a member of Clade IA, assembled following shotgun metagenomic sequencing of laboratory-scale bioreactor sludge. We estimate the genome to be 80–90% complete. Although the two clades share 16S rRNA sequence identity of >98.0%, we observed a remarkable lack of synteny between the two genomes. We identified 2317 genes shared between the two genomes, with an average nucleotide identity (ANI) of 78.3%, and accounting for 49% of genes in the UW-1 genome. Unlike UW-1, the UW-2 genome seemed to lack genes for nitrogen fixation and carbon fixation. Despite these differences, metabolic genes essential for denitrification and EBPR, including carbon storage polymer and polyphosphate metabolism, were conserved in both genomes. The ANI from genes associated with EBPR was statistically higher than that from genes not associated with EBPR, indicating a high selective pressure in EBPR systems. Further, we identified genomic islands of foreign origins including a near-complete lysogenic phage in the Clade IA genome. Interestingly, Clade IA appeared to be more phage susceptible based on it containing only a single Clustered Regularly Interspaced Short Palindromic Repeats locus as compared with the two found in Clade IIA. Overall, the comparative analysis provided a genetic basis to understand physiological differences and ecological niches of Accumulibacter populations, and highlights the importance of diversity in maintaining system functional resilience.

AbstractBackgroundHuanglongbing (HLB) is a worldwide devastating disease of citrus. There are no effective control measures for this newly emerging but century-old disease. Previously, we reported a combination of Penicillin G and Streptomycin was effective in eliminating or suppressing the associated bacterium, ‘CandidatusLiberibacter asiaticus’ (Las).ResultsHere we report the bacterial composition and community structure in HLB-affected citrus plants during a growing season and while being treated with antibiotic combinations PS (Penicillin G and Streptomycin) and KO (Kasugamycin and Oxytetracycline) using the Phylochip™ G3 array. Both antibiotic treatments resulted in significantly lower Las bacterial titers (Pr<0.05) and hybridization scores. Of the 50,000+ available operational taxonomic units (OTUs) on PhyloChip™ G3, 7,028 known OTUs were present in citrus leaf midribs. These OTUs were from 58 phyla, of which five contained 100 or more OTUs,Proteobacteria(44.1%), Firmicutes(23.5%),Actinobacteria(12.4%),Bacteroidetes(6.6%) andCyanobacteria(3.2%). In the antibiotic treated samples, the number of OTUs decreased to a total of 5,599. The over-all bacterial diversity decreased with the antibiotic treatments, as did the abundance of 11 OTUs withinProteobacteria,Firmicutes,BacteroidetesandPlanctomycetes. Within theProteobacteria, ten OTUs representing the classγ-proteobacteria increased in abundance after four months of treatment, when the Las bacterium was at its lowest level in the HLB-affected citrus field plants.ConclusionsOur data revealed thatProteobacteriawas constantly the dominant bacterial phylum recovered from citrus leaf midribs, with the α-proteobacterial and the γ-proteobacterial classes vying for prevalence. In addition, the level of bacterial diversity found in the leaf midribs of field citrus was greater than previously described. Bacterial cells in close proximity may be able to modify their microenvironment, making the composition of the microbial community an important factor in the ability of Las to cause HLB progression. A low Las level was seen as an annual fluctuation, part of the bacterial population dynamics, and as a response to the antibiotic treatments.

ABSTRACT A recently described clinical isolate, “ Candidatus Bartonella ancashi,” was obtained from a blood sample of a patient presenting with verruga peruana in the Ancash region of Peru. This sample and a second isolate obtained 60 days later from the same patient were molecularly typed using multilocus sequence typing (MLST) and multispacer sequence typing (MST). The isolates were 100% indistinguishable from each other but phylogenetically distant from Bartonella bacilliformis and considerably divergent from other known Bartonella species, confirming their novelty.

Two Gram-negative, facultatively anaerobic, rod-shaped bacteria, strains EF212Tand PS125T, were isolated from the octocoralsEunicea fuscaandPlexaurasp., respectively. EF212Twas isolated from a specimen ofE. fuscacollected off the coast of Florida, USA, and PS125Twas isolated from a specimen ofPlexaurasp. collected off the coast of Bimini, Bahamas. Analysis of the nearly full-length 16S rRNA gene sequences showed that these novel strains were most closely related toEndozoicomonas montiporaeCL-33T,E. elysicolaMKT110TandE. numazuensisHC50T(EF212T, 95.6–97.2 % identity; PS125T, 95.1–96.4 % identity). DNA–DNA hybridization values among EF212T, PS125T,E. montiporaeLMG 24815TandE. elysicolaKCTC 12372Twere far below the 70 % cut-off, with all values for duplicate measurements being less than 35 %. Both EF212Tand PS125Trequired NaCl for growth and showed optimal growth at 2–3 % NaCl, 22-30 °C and pH 8.0. The predominant cellular fatty acids were summed feature 3 (C16 : 1ω6cand/or C16 : 1ω7c), summed feature 8 (C18 : 1ω6cand/or C18 : 1ω7c), C16 : 0and C14 : 0. The DNA G+C content of EF212Twas 48.6 mol% and that of PS125Twas 47.5 mol%. In addition to the genotypic differences observed between the two novel strains and related type strains, phenotypic and chemotaxonomic experiments also revealed differences between strains. Thus, strains EF212Tand PS125Trepresent novel species of the genusEndozoicomonas, for which the namesEndozoicomonas euniceicolasp. nov. andEndozoicomonas gorgoniicolasp. nov., respectively, are proposed. The type strains are EF212T( = NCCB 100458T = DSM 26535T) forEndozoicomonas euniceicolasp. nov. and PS125T( = NCCB 100438T = CECT 8353T) forEndozoicomonas gorgoniicolasp. nov. An emended description of the genusEndozoicomonasis also provided to encompass differences observed in the results of genotypic, chemotaxonomic and phenotypic tests compared from the original and amended genus descriptions.