Publications

4365

Elm yellows phytoplasmas (EY) belonging to the 16SrV‐A subgroup were recently proposed as a new candidate species ‘ Candidatus Phytoplasma ulmi’. These pathogens infect elm trees, causing leaf yellowing and premature drying. In this study, 25 isolates originating from localities in northeast, east and southwest Serbia were characterized by means of RFLP analysis and DNA sequencing of four genomic loci: 16S rRNA, ribosomal protein rpl22 ‐ rps3 , secY and map . In total, five different genotypes were identified based on collective sequencing of all four genes. Four of these genotypes showed significant nucleotide changes compared with the EY1 T reference strain. Phylogeny based on parsimony analyses of ribosomal protein, secY and map genetic loci indicated a single monophyletic origin of EY1 T and the new ‘ Ca . Phytoplasma ulmi’ strains. Unlike phylogenetic clustering, DNA sequence comparison of EY1 T and the novel strains revealed mutations in oligonucleotide signature sequences for all three genes (16S, rpl22 ‐ rps3 and secY ) used for the characterization and assignment of 16SrV‐A phytoplasmas to the ‘ Ca.  Phytoplasma ulmi’ species in the original description. Based on their high degree of genetic variability, the Serbian strains were assigned to four different subtypes of ‘ Ca.  Phytoplasma ulmi’ (EY‐S1, EY‐S2, EY‐S3 and EY‐S4). New diagnostic enzymes for practical use in ‘ Ca.  Phytoplasma ulmi’ identification are proposed for the 16S rRNA, ribosomal protein and secY genes. The implications of genetic variability within signature sequences for taxonomy and identification of ‘ Ca . Phytoplasma’ species, as well as the importance of geographic variability and number of strains characterized for species description, are discussed.

Prophages are important genetic elements of bacterial genomes and are involved in lateral gene transfer, pathogenicity, environmental adaptations, and interstrain genetic variability. In this study, the sequence of a prophage terminase gene of ‘Candidatus Liberibacter asiaticus’, a bacterium associated with citrus Huanglongbing (HLB), was selected as a molecular marker to assess the genetic variation in two ‘Ca. L. asiaticus’ populations from geographically distinct provinces (Guangdong and Yunnan) in China. The frequency of the prophage terminase gene was 15.8% (19/120) in Guangdong (altitude <500 m) and 97.4% (38/39) in Yunnan (altitude >2,000 m). The difference was highly significant (P < 0.0001) based on χ2 analysis. However, the partial prophage terminase gene sequences obtained from 10 Guangdong strains and 6 Yunnan strains were identical or highly similar, suggesting that at least some bacterial strains in the two locations shared a common recent origin. This is the first report on population variation of ‘Ca. L. asiaticus’ in China, where HLB was first described. The population variation of ‘Ca. L. asiaticus’ in the two geographical regions and the related HLB epidemiology were discussed.

A novel actinomycete that was capable of degrading poly(l-lactic acid), strain CMU-PLA07T, was isolated from soil in northern Thailand. Strain CMU-PLA07T had biochemical, chemotaxonomic, morphological and physiological properties that were consistent with its classification in the genus Amycolatopsis. 16S rRNA gene sequence analysis showed that the isolate formed a phyletic line within the genus Amycolatopsis. Strain CMU-PLA07T was most similar to Amycolatopsis coloradensis IMSNU 22096T (99.5 % 16S rRNA gene sequence similarity) and Amycolatopsis alba DSM 44262T (99.4 %). However, strain CMU-PLA07T was distinguishable from the type strains of species of the genus Amycolatopsis on the basis of DNA–DNA relatedness and phenotypic data. Therefore, strain CMU-PLA07T is considered to represent a novel species of the genus Amycolatopsis, for which the name Amycolatopsis thailandensis sp. nov. is proposed. The type strain is CMU-PLA07T ( = JCM 16380T = BCC 38279T).

Abstract Candidatus Liberibacter asiaticus (Las) has been reported to increase the susceptibility of the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae), to selected insecticides. Reduced general esterase activity in Las-infected, compared with uninfected, D. citri has been proposed as a possible explanation for this difference in insecticide susceptibility. The current study was conducted to quantify glutathione transferase (GST) and cytochrome P450 (general oxidase) activities in Las-infected D. citri to further explain the possible mechanisms for altered susceptibility to insecticides due to Las infection. GST and cytochrome P450 activities (indirectly through general oxidase levels) were quantified in Las-infected and uninfected D. citri nymphs and adults. Mean (±SEM) GST activity was significantly lower in Las-infected (468.23 ± 26.87 /µmol/min/mg protein) than uninfected (757.63 ± 59.46 µmol/min/mg protein) D. citri adults. Likewise, mean cytochrome P450 activity was significantly lower in Las-infected (0.23 ± 0.02 equivalent units [EU] cytochrome P450/mg protein) than uninfected (0.49 ± 0.05 EU cytochrome P450/mg protein) D. citri adults. Immature stages (second and fifth instars) were characterized by significantly lower GST activity than adults for uninfected D. citri. However, cytochrome P450 activity was significantly higher in second instar nymphs than adults and fifth-instar nymphs for uninfected D. citri. Lower activities of GST and general oxidase in Las-infected D. citri indicate that infection with Las alters D. citri physiology in a manner that could increase insecticide susceptibility. The reduced activities of these detoxifying enzymes due to Las infection may be explained by examining expression levels of associated genes in Las-infected and uninfected D. citri.