Characterization of a non-sexual population of Strongyloides stercoralis with hybrid 18S rDNA haplotypes in Guangxi, Southern China

Abstract

Strongyloidiasis is a much-neglected but sometimes fatal soil born helminthiasis. The causing agent, the small intestinal parasitic nematode Strongyloides stercoralis can reproduce sexually through the indirect/heterogonic life cycle, or asexually through the auto-infective or the direct/homogonic life cycles. Usually, among the progeny of the parasitic females both, parthenogenetic parasitic (females only) and sexual free-living (females and males) individuals, are present simultaneously. We isolated S . stercoralis from people living in a village with a high incidence of parasitic helminths, in particular liver flukes ( Clonorchis sinensis ) and hookworms, in the southern Chinese province Guangxi. We determined nuclear and mitochondrial DNA sequences of individual S . stercoralis isolated from this village and from close by hospitals and we compared these S . stercoralis among themselves and with selected published S . stercoralis from other geographic locations. For comparison, we also analyzed the hookworms present in the same location. We found that, compared to earlier studies of S . stercoralis populations in South East Asia, all S . stercoralis sampled in our study area were very closely related, suggesting a recent common source of infection for all patients. In contrast, the hookworms from the same location, while all belonging to the species Necator americanus , showed rather extensive genetic diversity even within host individuals. Different from earlier studies conducted in other geographic locations, almost all S . stercoralis in this study appeared heterozygous for different sequence variants of the 18S rDNA hypervariable regions (HVR) I and IV. In contrast to earlier investigations, except for three males, all S . stercoralis we isolated in this study were infective larvae, suggesting that the sampled population reproduces predominantly, if not exclusively through the clonal life cycles. Consistently, whole genome sequencing of individual worms revealed higher heterozygosity than reported earlier for likely sexual populations of S . stercoralis . Elevated heterozygosity is frequently associated with asexual clonal reproduction.

Conserved nuclear hormone receptors controlling a novel plastic trait target fast-evolving genes expressed in a single cell

“…For most such lines, we extracted genomic DNA using GenElute Mammalian Genomic DNA Miniprep Kit (Merck), whereby we modified the tissue digestion step by raising the Proteinase K concentration to 2 mg/mL, and prepared next-generation sequencing (NGS) libraries using Nextera DNA Flex Library Prep Kit (Illumina). For the nhr-40 null mutant line, we followed a recently introduced cost-effective alternative procedure [77] with several modifications. Single worms were placed in 10 μL water, and frozen and thawed 3 times in liquid nitrogen.…”

Machine learning-based analyses support the existence of species complexes for Strongyloides fuelleborni and Strongyloides stercoralis

“…As cox1 is also encoded on the mitochondrion, it is not subject to heterozygosity. These features make cox1 conducive to an analysis by phylogenetic methods or clustering based on sequence similarity (Jaleta et al, 2017; Barratt et al, 2019b;Beknazarova et al, 2019;Zhou et al, 2019). Alternatively, the 18S rDNA locus may be heterozygous in some individuals of S. stercoralis (see Zhou et al, 2019), which is an important confounding factor for phylogenetic methods.…”

“…Hasegawa et al (2009) proposed HVRs I to IV of the 18S rDNA as useful markers for Strongyloides species diagnosis, especially HVR-IV, based on the observation that 'its nucleotide arrangements are mostly species specific'. HVR-I and HVR-IV are now routinely used in Strongyloides genotyping surveys (Barratt et al, 2019b;Zhou et al, 2019). The mitochondrial cytochrome c oxidase subunit 1 (cox1) locus of Strongyloides spp.…”

Seasonal Filarial Infections and Their Black Fly Vectors in Chiang Mai Province, Northern Thailand

“…Genomic DNA of individual larvae was extracted using the PureLink ® Genomic DNA Mini Kit (Invitrogen, Carlsbad, CA, USA). PCR amplification was conducted by using the primers and annealing temperatures listed in Table 4 with the reaction mixture of 20 µL, consisting of 1–2 µL of DNA template, 0.5 U of Taq DNA polymerase, 2–3 mM of MgCl 2 , 0.25 mM dNTPs, and 0.2 µM of each primer under PCR cycling conditions described elsewhere [ 15 , 43 ]. The amplified products were purified and sequenced following the methods mentioned in Section 4.3 .…”