Publications

4772

Summary A magnetotactic bacterium, designated strain LO‐1, of the Nitrospirae phylum was detected and concentrated from a number of freshwater and slightly brackish aquatic environments in southern Nevada. The closest phylogenetic relative to LO‐1 is Candidatus Magnetobacterium bavaricum based on a 91.2% identity in their 16S rRNA gene sequence. Chemical and cell profiles of a microcosm containing water and sediment show that cells of strain LO‐1 are confined to the oxic–anoxic interface and the upper regions of the anaerobic zone which in this case, occurred in the sediment. This microorganism is relatively large, ovoid in morphology and usually biomineralizes three braid‐like bundles of multiple chains of bullet‐shaped magnetosomes that appeared to be enclosed in a magnetosome membrane. Cells of LO‐1 had an unusual three‐layered unit membrane cell wall and contained several types of inclusions, some of which are sulfur‐rich. Strain LO‐1 is motile by means of a single bundle of sheathed flagella and exhibits the typical ‘wobbling’ motility and helical swimming (‘flight’) path of the magnetotactic cocci. This study and reports from others suggest that LO‐1‐like organisms are widespread in sediments of freshwater to brackish natural aquatic environments.

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.

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