Azevedo Nuno F, Bragança Sofia M, Simões Lúcia C, Cerqueira Laura, Almeida Carina, Keevil Charles W, Vieira Maria J
LEPAE, Department of Chemical Engineering, Faculty of Engineering, University of Porto, Portugal.
BMC Res Notes. 2012 Aug 8;5:422. doi: 10.1186/1756-0500-5-422.
Plating methods are still the golden standard in microbiology; however, some studies have shown that these techniques can underestimate the microbial concentrations and diversity. A nutrient shock is one of the mechanisms proposed to explain this phenomenon. In this study, a tentative method to assess nutrient shock effects was tested.
To estimate the extent of nutrient shock effects, two strains isolated from tap water (Sphingomonas capsulata and Methylobacterium sp.) and two culture collection strains (E. coli CECT 434 and Pseudomonas fluorescens ATCC 13525) were exposed both to low and high nutrient conditions for different times and then placed in low nutrient medium (R2A) and rich nutrient medium (TSA).The average improvement (A.I.) of recovery between R2A and TSA for the different times was calculated to more simply assess the difference obtained in culturability between each medium. As expected, A.I. was higher when cells were plated after the exposition to water than when they were recovered from high-nutrient medium showing the existence of a nutrient shock for the diverse bacteria used. S. capsulata was the species most affected by this phenomenon.
This work provides a method to consistently determine the extent of nutrient shock effects on different microorganisms and hence quantify the ability of each species to deal with sudden increases in substrate concentration.
平板接种法仍是微生物学中的金标准；然而，一些研究表明这些技术可能会低估微生物浓度和多样性。营养休克是为解释这一现象而提出的机制之一。在本研究中，测试了一种评估营养休克效应的初步方法。
为了估计营养休克效应的程度，从自来水中分离出的两种菌株（荚膜鞘氨醇单胞菌和甲基杆菌属）以及两种保藏菌株（大肠杆菌CECT 434和荧光假单胞菌ATCC 13525）在不同时间分别暴露于低营养和高营养条件下，然后置于低营养培养基（R2A）和丰富营养培养基（TSA）中。计算不同时间R2A和TSA之间恢复的平均改善率（A.I.），以便更简单地评估每种培养基在可培养性方面获得的差异。正如预期的那样，与从高营养培养基中恢复时相比，细胞在暴露于水后接种时的A.I.更高，这表明所使用的不同细菌存在营养休克。荚膜鞘氨醇单胞菌是受此现象影响最大的物种。
这项工作提供了一种方法，可一致地确定营养休克对不同微生物影响的程度，从而量化每个物种应对底物浓度突然增加的能力。
