Kim H W, Matin A, Rhee M S
Department of Food Bioscience and Technology, College of Life Sciences and Biotechnology, Korea University, Seoul, Republic of Korea.
Appl Environ Microbiol. 2014 Apr;80(7):2270-8. doi: 10.1128/AEM.04037-13. Epub 2014 Jan 31.
The aim of this study is to provide understanding of microgravity effects on important food-borne bacteria, Escherichia coli O157:H7 ATCC 35150, ATCC 43889, and ATCC 43895, cultured in nutrient-rich or minimal medium. Physiological characteristics, such as growth (measured by optical density and plating), cell morphology, and pH, were monitored under low-shear modeled microgravity (LSMMG; space conditions) and normal gravity (NG; Earth conditions). In nutrient-rich medium, all strains except ATCC 35150 showed significantly higher optical density after 6 h of culture under LSMMG conditions than under NG conditions (P < 0.05). LSMMG-cultured cells were approximately 1.8 times larger than NG-cultured cells at 24 h; therefore, it was assumed that the increase in optical density was due to the size of individual cells rather than an increase in the cell population. The higher pH of the NG cultures relative to that of the LSMMG cultures suggests that nitrogen metabolism was slower in the latter. After 24 h of culturing in minimal media, LSMMG-cultured cells had an optical density 1.3 times higher than that of NG-cultured cells; thus, the higher optical density in the LSMMG cultures may be due to an increase in both cell size and number. Since bacteria actively grew under LSMMG conditions in minimal medium despite the lower pH, it is of some concern that LSMMG-cultured E. coli O157:H7 may be able to adapt well to acidic environments. These changes may be caused by changes in nutrient metabolism under LSMMG conditions, although this needs to be demonstrated in future studies.
本研究的目的是了解微重力对在营养丰富或基本培养基中培养的重要食源细菌——大肠杆菌O157:H7 ATCC 35150、ATCC 43889和ATCC 43895的影响。在低剪切模拟微重力（LSMMG；太空条件）和正常重力（NG；地球条件）下监测其生理特征，如生长情况（通过光密度和菌落计数测量）、细胞形态和pH值。在营养丰富的培养基中，除ATCC 35150外，所有菌株在LSMMG条件下培养6小时后的光密度均显著高于NG条件下（P < 0.05）。在24小时时，LSMMG培养的细胞比NG培养的细胞大约大1.8倍；因此，推测光密度的增加是由于单个细胞的大小增加而非细胞数量增加。NG培养物的pH值相对于LSMMG培养物更高，这表明后者的氮代谢较慢。在基本培养基中培养24小时后，LSMMG培养的细胞光密度比NG培养的细胞高1.3倍；因此，LSMMG培养物中较高的光密度可能是由于细胞大小和数量的增加。由于尽管pH值较低，细菌在LSMMG条件下仍能在基本培养基中活跃生长，因此值得关注的是，LSMMG培养的大肠杆菌O157:H7可能能够很好地适应酸性环境。这些变化可能是由LSMMG条件下营养代谢的变化引起的，尽管这需要在未来的研究中得到证实。
