Publications

3887

The Rickettsiales-like prokaryote - Candidatus Xenohaliotis californiensis (Ca. Xc) – has decimated black abalone populations along the Pacific coast of North America. White abalone, – Haliotis sorenseni – are also susceptible and nearly extinct in the wild due to overfishing in the 1970s. Candidatus Xenohaliotis californiensis proliferates in epithelial cells of the abalone gastrointestinal tract and causes clinical signs of starvation. In 2012, evidence of a putative phage associated with Ca. Xc in Haliotis rufescens was described. In this study, we investigated the virulence of Ca. Xc in red and white abalone at different environmental temperatures in the presence of phage. Using a comparative experimental design, we observed differences over time between the two abalone species in mortality, body condition, and bacterial load by quantitative real time PCR (qPCR). By day 251, all white abalone exposed to the Ca. Xc and its phage in the warm water (18.5ºC) treatment died, while red abalone exposed to the same conditions had a mortality rate of 10% despite a relatively heavy bacterial burden as determined by qPCR of posterior esophagus tissue and histological assessment at the termination of the experiment. These data support the phage as a protective and potentially therapeutic agent for withering syndrome in red abalone, while white abalone appear to remain susceptible to this disease even in phage presence. These findings have important implications for implementation of a white abalone recovery program, particularly with respect to the thermal regimes of locations where captively-reared individuals will be outplanted.

“Candidatus Liberibacter europaeus” (Leu) is one of six currently known Liberibacter species. It is known primarily from pear and related species across Europe, and from Scotch broom and its associated psyllids in New Zealand (introduced from Britain). The psyllids were introduced to New Zealand as a biocontrol agent for broom and it is thought the bacterium may have been introduced as an endosymbiont of the psyllids. No symptoms in apple or pear trees have been reported, but mild symptoms can occur in broom. 16S and 16S–23S intergenic spacer region DNA sequences of this species are available from GenBank. Analysis of these sequences and associated ecological descriptions indicates the occurrence of two haplotypes, LeuA and LeuB, defined not only genetically but also by geographic range as well as by plant/psyllid host species composition. Liberibacter species are new to science and haplotype identifications enable historical accounts of relationships and spread to be generated.

Citrus production throughout the world is being severely threatened by Huanglongbing (HLB), which is a disease associated with the bacteria ‘Candidatus Liberibacter asiaticus’ (CLas), africanus, and americanus. This Resource Announcement provides amplicon-based next generation sequencing (NGS) datasets of the bacterial and fungal rRNA internal transcribed spacer (ITS) region from CLas-infected citrus budwood, leaves, and roots from five orchards located in different geographical regions in Florida (USA). To our knowledge, this is the first amplicon-based NGS study (i) that describes the fungal taxa associated with citrus and (ii) that provides comparative analyses of the bacterial and fungal taxa associated with budwood, leaves, and roots from the same citrus trees. This report also provides the sample metadata linked to these sequence datasets including HLB severity rating, tissue type, citrus rootstock, citrus scion, geographical region, and year trees were planted. When analyzed with other similar datasets, we anticipate that researchers will be able to obtain a greater understanding of the factors that shape the citrus microbiome as well as identify individual microorganisms or consortia of microorganisms that play a role in HLB suppression or exacerbation.