Biology subjects

Ruecker, A.

Publications and source records attributed to Ruecker, A..

3 recordsLinked to original sources

bioRxiv2020

Artemisinin-resistant malaria parasites show enhanced transmission to mosquitoes under drug pressure

Resistance to artemisinin combination therapy (ACT) in the Plasmodium falciparum parasite is threatening to reverse recent gains in reducing global deaths from malaria. Whilst resistance manifests as delayed asexual parasite clearance in patients following ACT treatment, the phenotype can only spread geographically via the sexual cycle and subsequent transmission through the mosquito. Artemisinin and its derivatives (such as dihydroartemisinin, DHA) as well as killing the asexual parasite form are known to sterilize male, sexual-stage gametes from activation. Whether resistant parasites overcome this artemisinin-dependent sterilizing effect has not, however, been fully tested. Here, we analysed five P. falciparum clinical isolates from the Greater Mekong Subregion, each of which demonstrated delayed clinical clearance and carried known resistance-associated polymorphisms in the Kelch13 gene (PfK13var). As well as demonstrating reduced sensitivity to artemisinin-derivates in in vitro asexual growth assays, certain PfK13var isolates also demonstrated a marked reduction in sensitivity to these drugs in an in vitro male gamete activation assay compared to a sensitive control. Importantly, the same reduction in sensitivity to DHA was observed when the most resistant isolate was assayed by standard membrane feeding assays using Anopheles stephensi mosquitoes. These results indicate that ACT use can favour resistant over sensitive parasite transmission. A selective advantage for resistant parasite transmission could also favour acquisition of further polymorphisms, such as mosquito host-specificity or antimalarial partner-drug resistance in mixed infections. Favoured transmission of resistance under ACT coverage could have profound implications for the spread of multidrug resistant malaria beyond Southeast Asia. ONE SENTENCE SUMMARYArtemisinin-resistant clinical isolates can also demonstrate resistance to the transmission-blocking effects of artemisinin-based drugs, favouring resistance transmission to the mosquito.

microbiology↗

bioRxiv2019

Metagenomic- and cultivation-based exploration of anaerobic chloroform biotransformation in hypersaline sediments as natural source of chloromethanes

Chloroform (CF) is an environmental contaminant that can be naturally formed in various environments ranging from forest soils to salt lakes. Here we investigated CF removal potential in sediments obtained from hypersaline lakes in Western Australia. Reductive dechlorination of CF to dichloromethane (DCM) was observed in enrichment cultures derived from sediments of Lake Strawbridge, which has been reported as a natural source of CF. The lack of CF removal in the abiotic control cultures without artificial electron donors indicated that the observed CF removal is a biotic process. Metabolite analysis with 13C labelled CF in the sediment-free enrichment cultures (pH 8.5, salinity 5%) revealed that increasing the vitamin B12 concentration from 0.04 to 4 M enhanced CF removal, reduced DCM formation, and increased 13CO2 production, which is likely a product of CF oxidation. Known organohalide-respiring bacteria and reductive dehalogenase genes were neither detected by quantitative PCR nor metagenomic analysis. Rather, members of the order Clostridiales, known to co-metabolically transform CF to DCM and CO2, were detected in the enrichment cultures. Genome-resolved metagenome analysis indicated that their genomes encode enzymatic repertoires for the Wood-Ljungdahl pathway and cobalamin biosynthesis that are known to be involved in co-metabolic CF transformation. ImportanceMore than 90% of the global CF emission to the atmosphere originates from natural sources, including saline environments such as salt lake sediments. However, knowledge about the microbial metabolism of CF in such extreme environments is lacking. Here we showed CF transformation potential in a hypersaline lake that was reported as a natural source of CF production. Application of interdisciplinary approaches of microbial cultivation, stable isotope labelling, and metagenomics aided in defining potential chloroform transformation pathways. This study indicates that microbiota may act as a filter to reduce CF emission from hypersaline lakes to the atmosphere, and expands our knowledge of halogen cycling in extreme hypersaline environments.

microbiology↗

bioRxiv2017

Failure of in vitro differentiation of Plasmodium falciparum gametocytes into ookinetes arises because of poor gamete fertilisation

A critical step towards malaria elimination will be the interruption of Plasmodium transmission from the human host to the mosquito. At the core of the transmission cycle lies Plasmodium sexual reproduction leading to zygote formation and mosquito midgut colonisation by ookinetes. Whilst in vitro ookinete culture from the murine and avian malaria parasites, Plasmodium berghei and P. gallinaceum, has greatly increased our knowledge of transmission biology; efforts to mimic the process in the human parasite P. falciparum have, to date, had only limited success. Using fluorescence microscopy and flow cytometry with antibodies specific to the male gametocyte and developing ookinetes, we sought to evaluate P. falciparum ookinete production using previously published in vitro protocols. We then compared in vitro versus in vivo ookinete production in both P. falciparum and P. berghei parasites, exploring potential barriers to complete development. Finally, we sought to test a wide range of literature-led culture conditions towards further optimisation of in vitro P. falciparum ookinete production. Despite extensive testing, our efforts to replicate published methods did not produce appreciable quantities of fully formed P. falciparum ookinetes in vitro. In parallel, however, gametocyte cultures that failed to differentiate fully in vitro successfully developed into ookinetes in vivo with an efficiency approximating that of P. berghei. Flow cytometry analysis showed that this disparity likely lies with the poor fertilization of P. falciparum gametes in vitro. Attempts to improve gametocyte fertility or define conditions more permissive to fertilisation/ookinete survival in vitro were also unsuccessful. Current in vitro conditions for P. falciparum ookinete production are not optimal for gamete fertilisation either due to the lack of parasite-species-specific mosquito factors missing from in vitro culture, or non-permissive cues contaminating culture preparations.

microbiology↗