Publications

4468

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.

The anaerobic nitrite-reducing methanotroph ‘CandidatusMethylomirabilis oxyfera’ (‘Ca.M. oxyfera’) produces oxygen from nitrite by a novel pathway. The major part of the O2is used for methane activation and oxidation, which proceeds by the route well known for aerobic methanotrophs. Residual oxygen may serve other purposes, such as respiration. We have found that the genome of ‘Ca.M. oxyfera’ harbours four sets of genes encoding terminal respiratory oxidases: two cytochromecoxidases, a third putativebo-type ubiquinol oxidase, and a cyanide-insensitive alternative oxidase. Illumina sequencing of reverse-transcribed total community RNA and quantitative real-time RT-PCR showed that all four sets of genes were transcribed, albeit at low levels. Oxygen-uptake and inhibition experiments, UV–visible absorption spectral characteristics and EPR spectroscopy of solubilized membranes showed that only one of the four oxidases is functionally produced by ‘Ca.M. oxyfera’, notably the membrane-boundbo-type terminal oxidase. These findings open a new role for terminal respiratory oxidases in anaerobic systems, and are an additional indication of the flexibility of terminal oxidases, of which the distribution among anaerobic micro-organisms may be largely underestimated.

Sida is a genus of flowering herbs in the family Malvaceae, which includes several species that are weeds in Brazil. Plants of a Sida sp. exhibiting symptoms characterized by stunting, chlorosis, small leaves, and witches'-broom, indicative of infection by phytoplasmas, were found in a field previously cultivated with tomato, located in the region of Campinas, State of São Paulo, in December 2008. To demonstrate the presence of phytoplasmas in diseased tissues, DNA was extracted from shoots and leaves from three symptomatic and eight asymptomatic plants. Nested PCR was performed using primers P1/Tint followed by primer pair R16F2n/R16R2 (1). DNA fragments of 1.2 kb, corresponding to 16S rDNA, were amplified only for DNA from two symptomatic samples. Phytoplasma identification was initially carried out by restriction fragment length polymorphism (RFLP) analysis through digesting the PCR products with the restriction enzymes AluI, HhaI, HaeIII, HpaII, MseI, and RsaI. The two phytoplasma isolates found to be infecting a Sida sp. showed identical RFLP patterns, which were indistinguishable from the phytoplasma previously reported in association with hibiscus (Hibiscus rosa-sinensis) witches'-broom in Brazil (2). Nucleotide sequence alignment revealed that 16S rDNA of both phytoplasma isolates found in a Sida sp. (GenBank Accession No. HQ230579) shared 99.9% sequence similarity with 16S rDNA from hibiscus witches'-broom phytoplasma (HibWB) (GenBank Accession No. AF147708). HibWB is the representative of the 16SrXV group and it was proposed as a putative species nominated “Candidatus Phytoplasma brasiliense” (2). The disease is frequently observed in hibiscus plants used as ornamentals in the states of São Paulo (4) and Rio de Janeiro (2). “Ca. Phytoplasma brasiliense” has only been reported in Brazil to be infecting hibiscus (2,4) and periwinkle (Catharanthus roseus) (3). The presence of a phytoplasma belonging to group 16SrXV in a Sida sp. expands its natural host range. The role of this weed as a potential source of inoculum for crops should be investigated. References: (1) I. M. Lee et al. Int. J. Syst. Bacteriol. 48:1153, 1998. (2) H. G. Montano et al. Int. J. Syst. Evol. Microbiol. 51:1109, 2001. (3) H. G. Montano et al. Plant Dis. 85:1209, 2001. (4) E. G. Silva et al. Summa Phytopathol. 35:234, 2009.

A thermotolerant, Gram-stain-positive, aerobic, sporangium-forming actinomycete, strain RA45T, was isolated from a desert region in Xinjiang Uigur Autonomous Region, north-western China. Comparative analysis of the 16S rRNA gene sequence and phenotypic characterization revealed that strain RA45Tbelonged phylogenetically to the familyPseudonocardiaceaeof the suborderPseudonocardineae. Strain RA45Tshowed more than 5 % 16S rRNA gene sequence divergence from recognized species of genera in the familyPseudonocardiaceae, forming a distinct lineage within the evolutionary radiation occupied by the generaAmycolatopsis,Prauserella,Thermocrispum,Saccharomonospora,SaccharopolysporaandSciscionella, but distinct from each of them. The affiliation to the family was supported by the presence of suborder- and family-specific 16S rRNA signature nucleotides, a DNA G+C content of 69.9 mol%, the presence ofmeso-diaminopimelic acid, ribose, arabinose, glucose and galactose, which are characteristic components of cell-wall chemotype IV of actinomycetes, the presence of menaquinone MK-9(H4) as the major respiratory lipoquinone, a lack of mycolic acids and the presence of anN-acetylated type of muramic acid. However, strain RA45Tdiffered from known genera of the family in its polar lipid composition: the major phospholipids were phosphatidylethanolamine, phosphatidylinositol mannosides, phosphatidylmethylethanolamine, diphosphatidylglycerol, phospholipids of unknown structure and phospholipids of unknown structure containing glucosamine (phospholipid type IV). Based on its morphological, chemotaxonomic and phylogenetic characteristics, strain RA45Tis considered to represent a novel species of a new genus in the familyPseudonocardiaceae, for which the nameYuhushiella desertigen. nov., sp. nov. is proposed. The type strain ofYuhushiella desertiis RA45T(=CGMCC 4.5579T=JCM 16584T).

AbstractBACKGROUND: Vector‐borne plant disease management can be enhanced by deployment of antifeedants in addition to the use of broad‐spectrum neurotoxic insecticides. The effects of pymetrozine on Asian citrus psyllid (ACP), Diaphorina citri Kuwayama, feeding behaviour, survival and transmission of Candidatus Liberibacter asiaticus (Las), the presumed causal pathogen of huanglongbing, were investigated.RESULTS: Pymetrozine applied at 52 and 104 µg mL−1 to citrus plants [Swingle citrumelo (X Citroncirus webberi Ingram and Moore)] modified the feeding behavior of ACP and increased the amount of time spent performing non‐penetration behaviors while decreasing the time spent performing ingestion behaviors compared with the controls 1 day after treatment. However, the antifeedant effect of pymetrozine subsided 5 days after application. Pymetrozine reduced the survival of both adults and nymphs on treated plants compared with the control. However, it had a greater impact on survival of nymphs than on survival of adults. Pymetrozine applied at 52 and 104 µg mL−1 on Las‐infected ‘Valencia’ sweet orange plants [Citrus sinensis L. (Osbeck)] reduced acquisition (12 and 21% respectively) and transmission (11 and 18% respectively) of Las by feeding ACP adults compared with the controls; however, these reductions were not statistically significant.CONCLUSIONS: Pymetrozine exhibited moderate antifeedant effects by modifying the feeding behavior of ACP adults with short residual activity. The impact of pymetrozine on survival of nymphs was greater than on adults at the higher concentrations tested. Pymetrozine also reduced the acquisition and transmission of Las by feeding ACP adults up to 21 and 18%, respectively, compared with untreated controls. Copyright © 2010 Society of Chemical Industry

Summary ‘ Candidatus Liberibacter spp.’ cause serious plant diseases. ‘ Candidatus Liberibacter asiaticus’, ‘ Ca. L. americanus’ and ‘ Ca. L. africanus’ are the aetiological agents of citrus greening (Huanglongbing) in Asia, America and Africa. ‘ Candidatus Liberibacter solanacearum’ causes diseases in Solanaceae in America and New Zealand. All four species are vectored by psyllid insects of different genera. Here, we show that the pear psyllid pest Cacopsylla pyri (L.) hosts a novel liberibacter species that we named ‘ Ca. Liberibacter europaeus’. It can bloom to high titres in the psyllid host, with more than 10 9 16S rRNA gene copies per individual. Fluorescent in situ hybridization experiments showed that ‘ Ca. L. europaeus’ is present in the host midgut lumen, salivary glands and Malpighian tubules. ‘ Candidatus L. europaeus’ has a relatively high prevalence (> 51%) in C. pyri from different areas in the Piedmont and Valle d'Aosta regions in Italy and can be transmitted to pear plants in experimental transmission trials. However, even though high titres of the bacterium (more than 10 8 16S rRNA gene copies g −1 of pear plant tissue) could be detected, in the pear tissues no specific disease symptoms could be observed in the infected plants over a 6‐month period. Despite liberibacters representing potential quarantine organisms, ‘ Ca. L. europaeus’, first described in Italy and Europe, apparently behaves as an endophyte rather than a pathogen.