To protect Mars from microbial contamination, research on growth of microorganisms found in spacecraft assembly clean rooms under simulated Martian conditions is required. This study investigated the effects of low atmospheric pressure on the growth of chemoorganotrophic spacecraft bacteria and whether the addition of Mars relevant anaerobic electron acceptors might enhance growth. The 125 bacteria screened here were recovered from actual Mars spacecraft. Growth at 7 hPa, 0 °C, and a CO2-enriched anoxic atmosphere (called low-PTA conditions) was tested on five TSA-based media supplemented with anaerobic electron acceptors. None of the 125 spacecraft bacteria showed active growth under the tested low-PTA conditions and amended media. In contrast, a decrease in viability was observed in most cases. Growth curves of two hypopiezotolerant strains, Serratia liquefaciens and Trichococcus pasteurii, were performed to quantify the effects of the added anaerobic electron acceptors. Slight variations in growth rates were determined for both bacteria. However, the final cell densities were similar for all media tested, indicating no general preference for any specific anaerobic electron acceptor. By demonstrating that a broad diversity of chemoorganotrophic and culturable spacecraft bacteria do not grow under the tested conditions, we conclude that there may be low risk of growth of chemoorganotrophic bacteria typically recovered from Mars spacecraft during planetary protection bioburden screenings.

译文

为了保护火星免受微生物污染,需要研究在模拟火星条件下在航天器组件洁净室中发现的微生物的生长。这项研究调查了低大气压对化学有机营养航天器细菌生长的影响,以及添加火星相关的厌氧电子受体是否可能促进生长。这里筛选的125细菌是从实际的火星航天器中回收的。在5种补充有厌氧电子受体的基于TSA的培养基上测试了7 hPa,0 °C和CO2-enriched缺氧气氛 (称为低PTA条件) 下的生长。在测试的低PTA条件和修正的培养基下,没有125航天器细菌显示出活跃的生长。相反,在大多数情况下观察到生存能力下降。进行了两种低唑的生长曲线,即沙雷氏菌和巴氏曲霉,以量化添加的厌氧电子受体的作用。确定了两种细菌的生长速率略有变化。但是,所有测试的培养基的最终细胞密度相似,表明对任何特定的厌氧电子受体都没有普遍偏爱。通过证明在测试条件下不会生长广泛的化学有机营养和可培养的航天器细菌,我们得出结论,在行星保护生物负荷筛选期间,通常从火星航天器中回收的化学有机营养细菌的生长风险可能较低。

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