Simulated microgravity promotes horizontal gene transfer of antimicrobial resistance genes between bacterial genera in the absence of antibiotic selective pressure

Bacteria are able to adapt and survive in harsh and changing environments through many mechanisms, with one of them being horizontal gene transfer (HGT). This process is one of the leading culprits in the spread of antimicrobial resistance within bacterial communities and could pose a significant health threat to astronauts if they fell ill, especially on long duration space missions. In order to better understand the degree of HGT activity that could be occurring in space, biosafety level-2, donor and recipient bacteria, were co-cultured under simulated microgravity (SMG) on Earth with concomitant 1G controls. Two antimicrobial resistance genes, blaOXA500 and ISAba1 from the donor, Acinetobacter pittii, were tracked in four recipient strains of Staphylococcus aureus (which did not harbor those genes) using polymerase chain reaction. All four S. aureus strains that were co-cultured with A. pittii under SMG had significantly higher number of isolates that were now blaOXA500 and ISAba1 positive compared to growth at 1G. The acquisition of these genes by the recipient induced a phenotypic change, as these isolates were now resistant to oxacillin, which they were previously susceptible to. This is a novel study, presenting for the first time, the increased HGT activity under SMG and the impact of the space environment in promoting increased gene dissemination within bacterial communities.

细菌可通过多种机制适应并在严苛多变的环境中存活，其中水平基因转移（horizontal gene transfer, HGT）是核心途径之一。该过程是细菌群落内抗菌耐药性传播的主要诱因之一，若宇航员患病，其可能构成严重的健康威胁，在长期太空任务中尤为如此。为更好地探究太空环境中可能发生的HGT活性水平，研究以生物安全二级的供体与受体细菌为对象，在地球环境下开展模拟微重力（simulated microgravity, SMG）共培养实验，并以1G重力条件作为平行对照。以皮氏不动杆菌（Acinetobacter pittii）作为供体，其携带的两种抗菌耐药基因blaOXA500与ISAba1，通过聚合酶链式反应在四株未携带该类基因的金黄色葡萄球菌（Staphylococcus aureus）受体菌株中进行追踪检测。相较于1G重力培养条件，经模拟微重力与皮氏不动杆菌共培养的全部四株金黄色葡萄球菌菌株，其获得blaOXA500与ISAba1基因的分离菌落数量均显著更高。受体菌株获得此类基因后引发了表型变化，这些分离菌落如今对原本易感的苯唑西林产生了耐药性。本研究为全新探索，首次揭示了模拟微重力环境下HGT活性增强的现象，以及太空环境对细菌群落内基因扩散的促进作用。