Department of Chemical Engineering, McGill University, Montreal, Quebec H3A 2B2, Canada.
Department of Civil Engineering, McGill University, Montreal, Quebec H3A 2K6, Canada.
Water Res. 2014 Jul 1;58:239-47. doi: 10.1016/j.watres.2014.03.048. Epub 2014 Apr 3.
In cold climate regions, microorganisms in upper layers of soil are subject to low temperatures and repeated freeze-thaw (FT) conditions during the winter. We studied the effects of cold temperature and FT cycles on the viability and survival strategies (namely motility and biofilm formation) of the common soil bacterium and model pathogen Bacillus subtilis. We also examined the effect of FT on the transport behavior of B. subtilis at two solution ionic strengths (IS: 10 and 100 mM) in quartz sand packed columns. Finally, to study the mechanical properties of the bacteria-surface bond, a quartz crystal microbalance with dissipation monitoring (QCM-D) was used to monitor changes in bond stiffness when B. subtilis attached to a quartz substrate (model sand surface) under different environmental conditions. We observed that increasing the number of FT cycles decreased bacterial viability and that B. subtilis survived for longer time periods in higher IS solution. FT treatment decreased bacterial swimming motility and the transcription of flagellin encoding genes. Although FT exposure had no significant effect on the bacterial growth rate, it substantially decreased B. subtilis biofilm formation and correspondingly decreased the transcription of matrix production genes in higher IS solution. As demonstrated with QCM-D, the bond stiffness between B. subtilis and the quartz surface decreased after FT. Moreover, column transport studies showed higher bacterial retention onto sand grains after exposure to FT. This investigation demonstrates how temperature variations around the freezing point in upper layers of soil can influence key bacterial properties and behavior, including survival and subsequent transport.
在寒冷气候地区，土壤上层的微生物在冬季会经历低温和反复的冻融（FT）条件。我们研究了冷温度和 FT 循环对常见土壤细菌和模式病原体枯草芽孢杆菌的生存能力和生存策略（即运动性和生物膜形成）的影响。我们还研究了 FT 对枯草芽孢杆菌在石英砂填充柱中两种溶液离子强度（IS：10 和 100mM）下运移行为的影响。最后，为了研究细菌-表面键的机械性能，使用石英晶体微天平（QCM-D）监测耗散监测（QCM-D），以监测枯草芽孢杆菌在不同环境条件下附着在石英基底（模型砂表面）时键刚度的变化。我们观察到，FT 循环次数的增加会降低细菌的生存能力，而在较高的 IS 溶液中，枯草芽孢杆菌的存活时间更长。FT 处理降低了细菌的游动能力和鞭毛编码基因的转录。尽管 FT 暴露对细菌生长速率没有显著影响，但它大大降低了枯草芽孢杆菌在较高 IS 溶液中的生物膜形成能力，并相应降低了基质产生基因的转录。正如 QCM-D 所证明的那样，FT 后枯草芽孢杆菌与石英表面之间的键刚度降低。此外，柱传输研究表明，FT 暴露后，细菌在砂粒上的保留率更高。这项研究表明，土壤上层接近冰点的温度变化如何影响关键的细菌特性和行为，包括生存和随后的运输。
