Alreshidi Mousa M, Dunstan R Hugh, Macdonald Margaret M, Gottfries Johan, Roberts Tim K
Department of Biology, College of Sciences, University of Ha'il, Ha'il, Saudi Arabia.
Metabolic Research Group, Faculty of Science, School of Environmental and Life Sciences, University Drive, Callaghan, NSW, Australia.
Front Microbiol. 2020 Jan 23;10:3059. doi: 10.3389/fmicb.2019.03059. eCollection 2019.
is an important pathogen that is associated with nosocomial infections, as well as food poisoning. This bacterium is resistant to antimicrobial agents and can survive in a wide range of environmental conditions. The aim of this study was to measure the uptake and release of amino acids by at mid-exponential and stationary phases of growth following exposure to a combination of conditions including variations in temperature, pH and NaCl. Bacterial cells were grown up to mid-exponential and stationary phases in tryptic soy broth (TSB), where the supernatants were collected for analyses of amino acids to determine the uptake and release characteristics. The uptake/release of amino acids was estimated by subtracting the initial levels of the free amino acids in the media from those measured at mid-exponential and stationary phases of growth. When cells were grown at ideal conditions, the analyses revealed that significant uptake of amino acids had occurred by stationary phase compared with the mid-exponential phase. A substantial release of valine and tyrosine into the external media was observed by cells at stationary phase. At both phases, the uptake and release patterns were significantly different between cells grown under ideal control conditions, when compared with those grown under various combinations of sub-optimal environmental conditions. The analyses of the supernatants harvested from controls and treatment groups at exponential phase indicated that the total uptake of amino acids was reduced approximately five times by cells grown with addition of 2.5% NaCl or with pH6 at 35°C, and 2-fold by cells grown at pH8 at 35°C. However, the final quantities of amino acids taken up by cells grown to stationary phase did not significantly alter between control and treated samples. Valine was found to be the most abundant amino acid that was significantly released into the media at stationary phase by both control and treated samples. It was evident that diverse environmental conditions resulted in differential patterns of amino acid uptake and release during adaptation to designated conditions.
是一种重要的病原体，与医院感染以及食物中毒有关。这种细菌对抗菌剂具有抗性，并且能够在广泛的环境条件下存活。本研究的目的是测量在暴露于包括温度、pH值和氯化钠变化在内的多种条件组合后，处于处于于生长的指数中期和稳定期的氨基酸摄取和释放情况。细菌细胞在胰蛋白胨大豆肉汤（TSB）中生长至指数中期和稳定期，收集上清液用于氨基酸分析以确定摄取和释放特征。通过从生长的指数中期和稳定期所测量的氨基酸水平中减去培养基中游离氨基酸的初始水平来估计氨基酸的摄取/释放。当细胞在理想条件下生长时，分析显示与指数中期相比，稳定期氨基酸有显著摄取。观察到稳定期的细胞向外部培养基中大量释放缬氨酸和酪氨酸。在两个阶段，与在次优环境条件的各种组合下生长的细胞相比，在理想对照条件下生长的细胞的摄取和释放模式存在显著差异。对指数期从对照组和处理组收获的上清液的分析表明，添加2.5%氯化钠或在35°C下pH值为6培养的细胞，氨基酸的总摄取量减少了约五倍，在35°C下pH值为8培养的细胞，氨基酸总摄取量减少了两倍。然而，生长至稳定期的细胞摄取的氨基酸最终量在对照样品和处理样品之间没有显著变化。发现缬氨酸是在稳定期由对照样品和处理样品显著释放到培养基中的最丰富的氨基酸。很明显，不同的环境条件在适应指定条件期间导致了氨基酸摄取和释放的不同模式。
