Publications

4938

The Asian citrus psyllid, Diaphorina citri, is an invasive insect and a vector of ‘ Candidatus Liberibacter asiaticus’ ( CLas), a bacterium whose growth in Citrus species results in huanglongbing (HLB), also known as citrus greening disease. Methods to enrich and sequence CLas from D. citri often rely on biased genome amplification and nevertheless contain significant quantities of host DNA. To overcome these hurdles, we developed a simple pretreatment DNase and filtration (PDF) protocol to remove host DNA and directly sequence CLas and the complete, primarily uncultivable microbiome from D. citri adults. The PDF protocol yielded CLas abundances upward of 60% and facilitated direct measurement of CLas and endosymbiont replication rates in psyllids. The PDF protocol confirmed our lab strains derived from a progenitor Florida CLas strain and accumulated 156 genetic variants, underscoring the utility of this method for bacterial strain tracking. CLas genetic polymorphisms arising in lab-reared psyllid populations included prophage-encoding regions with key functions in CLas pathogenesis, putative antibiotic resistance loci, and a single secreted effector. These variants suggest that laboratory propagation of CLas could result in different phenotypic trajectories among laboratories and could confound CLas physiology or therapeutic design and evaluation if these differences remain undocumented. Finally, we obtained genetic signatures affiliated with Citrus nuclear and organellar genomes, entomopathogenic fungal mitochondria, and commensal bacteria from laboratory-reared and field-collected D. citri adults. Hence, the PDF protocol can directly inform agricultural management strategies related to bacterial strain tracking, insect microbiome surveillance, and antibiotic resistance screening.

Grapevine yellows is one of the most damaging phytoplasma-associated diseases worldwide. It is linked to several phytoplasma species, which can vary regionally due to phytoplasma and insect-vector diversity. Specific, rapid, and reliable detection of the grapevine yellows pathogen has an important role in phytoplasma control. The purpose of this study was to develop and validate a specific loop-mediated isothermal amplification (LAMP) assay for detection of a distinct strain of grapevine ‘Candidatus Phytoplasma asteris’ that is present in South Africa, through implementation of a genome-informed test design approach. Several freely available, user-friendly, web-based tools were coupled to design the specific LAMP assays. The criteria for selection of the assays were set for each step of the process, which resulted in four experimentally operative LAMP assays that targeted the ftsH/hflB gene region, specific to the aster yellows phytoplasma strain from South Africa. A real-time PCR was developed, targeting the same genetic region, to provide extensive validation of the LAMP assay. The validated molecular assays are highly specific to the targeted aster yellows phytoplasma strain from South Africa, with good sensitivity and reproducibility. We show a genome-informed molecular test design and an efficient validation approach for molecular tests if reference and sample materials are sparse and hard to obtain. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Anaerobic ammonium oxidation (Anammox) process is a type of biological nitrogen removal technology which is known to directly convert ammonium and nitrite to nitrogen gas. The freshwater ‘Candidatus Kuenenia stuttgartiensis’ anammox under the phylum of Planctomycetes is used to study the parameters that affect the anammox development and the metabolic pathways alongside the associated enzymes. These observations were made using state-of-the art techniques for detecting anammox bacteria based on their small-subunit ribosomal RNA genes, functional genes and unique reaction pathways. This review systematically summarizes up-to-date studies on the parameters affecting the growth of the anammox bacteria and metabolic networks driving anammox bacterial anabolism and mixotrophy beyond genome-based predictions. The K. stuttgartiensis survives in summer and winter conditions besides in the aerobic zones (dissolved oxygen >2 mg/L), which consequently contribute to better nitrogen removal in the wastewater treatment. Furthermore, the K. stuttgartiensis utilizes the Wood–Ljungdahl pathway to directly assimilate extracellular formation instead of oxidising it completely to CO2 prior reassimilation.