Laubscher, M. | Search bioRxiv

bioRxiv2025

Digital PCR detection of Mycobacterium tuberculosis and HIV-1 co-localization in spinal tuberculosis biopsies

BackgroundMycobacterium tuberculosis (Mtb) and HIV-1 co-infection in tissues is suggested to favour reciprocal replication, infection and reservoir expansion. Yet, confirmation of this detrimental synergism in diseased tissues is limited. MethodsIn this prospective study of 25 adults investigated for spinal tuberculosis (STB) in South Africa (13 (52%) people living with HIV-1 (PLWH), on antiretroviral treatment) 25 open surgery or CT-guided biopsies were collected and portioned into 93 segments. Extracted DNA was analysed by droplet digital PCR (ddPCR) to detect and quantify Mtb complex (MTBC) (rpoB, IS6110), HIV-1 (pol, gag) and Human (RPP30) gene copies. ddPCR sensitivity for Mtb was validated against Xpert-Ultra and culture. Total biopsy and intra-biopsy variation in pathogen DNA abundance, co-detection, and relationships to human cellularity, HIV status, and peripheral viral load (VL) evaluated. ResultsddPCR detected MTBC DNA in biopsies from 10/10 (100%) culture-confirmed STB, 5/6 (83%) Xpert Ultra-confirmed STB and 4/9 (44%) diagnosed Not STB (all 4 with previous pulmonary TB). Detected MTBC ranged from 8-59,144 rpoB copies/biopsy. RpoB copies/million human cells were higher in biopsies from PLWH (p=0.0096) and positively correlated with matched-segment HIV-1 pol copies/million cells (r=0.40; p=0.0003), but not VL. HIV-1 DNA was detected in all PLWH biopsies, four with undetectable VL. HIV-1 pol copies/million cells were higher in segments with MTBC DNA co-detected (p=0.011) and also correlated with VL (r=0.91; p=0.0003). ConclusionsReciprocal relationships exists between Mtb and HIV-1 abundance in spinal tissue. Findings support investigating TB-HIV co-infected tissue segments to characterise how the immune microenvironment impacts HIV-1/Mtb reservoir persistence and/or expansion.

molecular biology↗

bioRxiv2019

Successful mating and hybridisation in two closely related flatworm species despite significant differences in reproductive morphology and behaviour

Speciation is usually a gradual process, in which reproductive barriers between two species accumulate over time. Reproductive traits, like genital morphology and mating behaviour, are some of the fastest diverging characters and can serve as reproductive barriers. The free-living flatworm Macrostomum lignano, an established model for studying sex in hermaphrodites, and its congener M. janickei are closely related, but differ substantially in their male intromittent organ (stylet) morphology. Here, we examine whether these morphological differences are accompanied by differences in behavioural traits, and whether these could represent barriers to successful mating and hybridization between the two species. Our data shows that the two species differ in many aspects of their mating behaviour, with M. janickei having a five-fold longer copulation duration, copulating less frequently, and having a longer and more delayed suck behaviour (a postcopulatory behaviour likely involved in sexual conflict). Interestingly, and despite these significant morphological and behavioural differences, the two species mate readily with each other in heterospecific pairings, often showing behaviours of intermediate duration. Although both species have similar fecundity in conspecific pairings, the heterospecific pairings revealed clear postmating barriers, as only few heterospecific pairings produced F1 hybrids. These hybrids had a stylet morphology that was intermediate between that of the parental species, and they could successfully backcross to both parental species. Finally, in a mate choice experiment we tested if the worms preferentially mated with conspecifics over heterospecifics, since such a preference could represent a premating barrier. Interestingly, the experiment showed that the nearly two-fold higher mating rate of M. lignano caused it to mate more with conspecifics, leading to assortative mating, while M. janickei ended up mating more with heterospecifics. Thus, while the two species can hybridize, the mating rate differences could possibly lead to higher fitness costs for M. janickei compared to M. lignano.

animal behavior and cognition↗