Publications

4454

AbstractSome entomopathogenic fungi species, Isaria fumosorosea, and Hirsutella citriformis were found to be efficient against the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae). However, the susceptibility to these fungi increases when the psyllid infected with Candidatus Liberibacter asiaticus (Las), which is transmitted by D. citri and causes citrus greening disease. In this study, we examined the Las‐infected and Las‐uninfected D. citri susceptibility to entomopathogenic fungi at different temperature regimes (5–40°C). When D. citri adults exposed to cold temperature (5°C), they showed less susceptibility to entomopathogenic fungi as compared with control (27°C). Irrespective of infection with Las, a significantly positive correlation was observed between temperature and percentage mortality caused by different isolates of I. fumosorosea, 3A Ifr, 5F Ifr, PS Ifr, and H. citriformis isolates, HC3D and 2H. In contrast, a significantly negative correlation was found between temperature and percentage mortality for 3A Ifr for both Las‐infected and Las‐uninfected psyllids. Detoxification enzymes, Glutathione S‐transferase levels in D. citri showed a negative correlation, whereas cytochrome P450 and general esterase levels were not correlated with changes in temperature. These findings revealed that detoxification enzymes and general esterase levels are not correlated with altered susceptibility to entomopathogenic fungi at the different temperature regimes. Conclusively, temperature fluctuations tested appear to be a significant factor impacting the management strategies of D. citri using entomopathogenic fungi.

The oxidative (H2O2) burst is a seminal feature of the basal plant defense response to attempted pathogen invasions. In ‘Candidatus Liberibacter asiaticus’ UF506, expression of the SC2 prophage-encoded secreted peroxidase (F489_gp15) increases bacterial fitness and delays symptom progression in citrus. Two chromosomal 1-Cys peroxiredoxin genes, CLIBASIA_RS00940 (Lasprx5) and CLIBASIA_RS00445 (Lasbcp), are conserved among all sequenced ‘Ca. L. asiaticus’ strains, including those lacking prophages. Both LasBCP and LasdPrx5 have only a single conserved peroxidatic Cys (CP/SH) and lack the resolving Cys (CR/SH). Lasprx5 appeared to be a housekeeping gene with similar moderate transcript abundance in both ‘Ca. L. asiaticus’–infected psyllids and citrus. By contrast, Lasbcp was expressed only in planta, similar to the expression of the SC2 peroxidase. Since ‘Ca. L. asiaticus’ is uncultured, Lasbcp and Lasprx5 were functionally validated in a cultured surrogate species, Liberibacter crescens, and both genes significantly increased oxidative stress tolerance and cell viability in culture. LasBCP was nonclassically secreted and, in L. crescens, conferred 214-fold more resistance to tert-butyl hydroperoxide (tBOOH) than wild type. Transient overexpression of Lasbcp in tobacco suppressed H2O2-mediated transcriptional activation of RbohB, the key gatekeeper of the systemic plant defense signaling cascade. Lasbcp expression did not interfere with the perception of ‘Ca. L. asiaticus’ flagellin (flg22Las) but interrupted the downstream activation of RbohB and stereotypical deposition of callose in tobacco. Critically, LasBCP also protected against tBOOH-induced peroxidative degradation of lipid membranes in planta, preventing subsequent accumulation of antimicrobial oxylipins that can also trigger the localized hypersensitive cell death response.

AbstractBased on molecular data, previous studies have suggested a high overall diversity and co‐infection rates of Bartonella bacteria in wild rodents and their fleas. However, partial genetic characterization of uncultured co‐infecting bacteria limited sound conclusions concerning intra‐ and inter‐specific diversity of the circulating Bartonella. To overcome this limitation, Bartonella infections of wild populations of two sympatric gerbil species and their fleas were explored by multiple isolations of Bartonella organisms. Accordingly, 448 pure Bartonella isolates, obtained from 20 rodent blood and 39 flea samples, were genetically characterized to the genotype and species levels. Results revealed a remarkable diversity and co‐infection rates of Bartonella among these sympatric rodents and their associated fleas. Specifically, 38 genotypes, classified into four main Bartonella species, were identified. Co‐infection was confirmed in 56% of the samples, which contained two to four Bartonella genotypes per sample, belonging to up to three different species. Recombination within and between these species was demonstrated, serving as a direct evidence of the frequent bacteria–bacteria interactions. Moreover, despite the noticeable interchange of common Bartonella genotypes between rodents and fleas, the co‐occurrence of genotypes was not random and differences in the overall diversity, and the ecological and phylogenetic similarities of the infection compositions were significantly associated with the carrier type (rodent vs. flea) and the rodent species. Thus, comprehensive identification of the co‐infecting organisms enabled the elucidation of ecological factors affecting the Bartonella distribution among reservoirs and vectors. This study may serve as a model for the investigation of other vector‐borne organisms and their relationships with Bartonella.

Specific scopeThis Standard describes the procedures for inspection of places of production of plants for planting which are susceptible to ‘Candidatus Phytoplasma pyri’. The scope of a place of production inspection may be for export, for internal country movements of materials or as an element of a national survey. Further inspections would be needed to determine freedom of a country or area from the pest concerned. This Standard does not cover eradication or containment measures in infested areas or measures needed to establish and maintain pest‐free places of production within areas where the pest is known to occur. It provides more detailed guidance to supplement EPPO Standard PM 3/76 (1) Trees of Malus, Pyrus, Cydonia and Prunus spp. – inspection of places of production.

AbstractRickettsialesare a lineage of obligatorily intracellularAlphaproteobacteria, encompassing important human pathogens, manipulators of host reproduction, and mutualists. Here we report the discovery of a novelRickettsialesbacterium associated withParamecium, displaying a unique extracellular lifestyle, including the ability to replicate outside host cells. Genomic analyses show that the bacterium possesses a higher capability to synthesize amino acids, compared to all investigatedRickettsiales. Considering these observations, phylogenetic and phylogenomic reconstructions, and re-evaluating the different means of interaction ofRickettsialesbacteria with eukaryotic cells, we propose an alternative scenario for the evolution of intracellularity inRickettsiales. According to our reconstruction, theRickettsialesancestor would have been an extracellular and metabolically versatile bacterium, while obligate intracellularity and genome reduction would have evolved later in parallel and independently in different sub-lineages. The proposed new scenario could impact on the open debate on the lifestyle of the last common ancestor of mitochondria withinAlphaproteobacteria.