美国科学家发现绿脓杆菌在失重环境下比在地球上更易繁殖

美国伦斯勒理工学院化学与生物工程学院的研究人员发现，细菌在失重环境下比在地球上更容易繁殖，特别是在缺乏营养的条件下，差异性更明显。相关文章发表于2013年11月06日的《BMC Microbiology》杂志上。

美国科学家发现绿脓杆菌在失重环境下比在地球上更易繁殖

在未来，宇航员可能需要应对新的敌人：太空细菌。科学家已经发现，绿脓杆菌在失重环境下比在地球上更易繁殖，即使在缺乏营养物的条件下也是如此。这是一种常见的医疗器械污染物和尿路感染的罪魁祸首。

2011年7月，研究人员在地球实验室和亚特兰蒂斯号航天飞机上的模拟尿液中培养该细菌(试验装置如图所示)。在一些样本中，研究人员大幅度降低了溶解的磷酸和氧气的浓度，并对一种水循环设备的内在条件进行了模拟，该设备可以把尿液转换成水，以便在长期的太空任务中循环利用。

当营养充足时，无重力条件下的细菌的生长速度——特别是72小时后细胞的浓度——和地球上的细菌是一样的。当营养匮乏时，地球上的细菌并不能像营养充足时一般快速生长，而无重力条件下的细菌却如营养充足时一般茁壮生长。

研究人员表示，差异的原因还不清楚，但是该发现意味着由人带入太空站和宇宙飞船中的细菌，只要给予足够的时间，有可能达到比在地球上类似的条件下更高的浓度——即使在缺乏营养物的条件下。

除了帮助科学家更好地了解绿脓杆菌在航天器中大量繁殖的风险或可能在宇航员中导致的疾病(诸如尿路感染)，该试验可能有助于科学家预测是否存在其他种类的细菌在太空中传播的可能。

原文摘要：

Effect of spaceflight on Pseudomonas aeruginosa final cell density is modulated by nutrient and oxygen availability

Wooseong Kim, Farah K Tengra, Jasmine Shong, Nicholas Marchand, Hon Kit Chan, Zachary Young, Ravindra C Pangule, Macarena Parra, Jonathan S Dordick, Joel L Plawsky and Cynthia H Collins

Background

Abundant populations of bacteria have been observed on Mir and the International Space Station. While some experiments have shown that bacteria cultured during spaceflight exhibit a range of potentially troublesome characteristics, including increases in growth, antibiotic resistance and virulence, other studies have shown minimal differences when cells were cultured during spaceflight or on Earth. Although the final cell density of bacteria grown during spaceflight has been reported for several species, we are not yet able to predict how different microorganisms will respond to the microgravity environment. In order to build our understanding of how spaceflight affects bacterial final cell densities, additional studies are needed to determine whether the observed differences are due to varied methods, experimental conditions, or organism specific responses.

Results

Here, we have explored how phosphate concentration, carbon source, oxygen availability, and motility affect the growth of Pseudomonas aeruginosa in modified artificial urine media during spaceflight. We observed that P. aeruginosa grown during spaceflight exhibited increased final Cell density relative to normal gravity controls when low concentrations of phosphate in the media were combined with decreased oxygen availability. In contrast, when the availability of either phosphate or oxygen was increased, no difference in final cell density was observed between spaceflight and normal gravity. Because motility has been suggested to affect how microbes respond to microgravity, we compared the growth of wild-type P. aeruginosa to a ΔmotABCD mutant deficient in swimming motility. However, the final cell densities observed with the motility mutant were consistent with those observed with wild type for all conditions tested.

Conclusions

These results indicate that differences in bacterial final cell densities observed between spaceflight and normal gravity are due to an interplay between microgravity conditions and the availability of substrates essential for growth. Further, our results suggest that microbes grown under nutrient-limiting conditions are likely to reach higher cell densities under microgravity conditions than they would on Earth. Considering that the majority of bacteria inhabiting spacecrafts and space stations are likely to live under nutrient limitations, our findings highlight the need to explore the impact microgravity and other aspects of the spaceflight environment have on microbial growth and physiology.