Abstract
Streptococcus thermophilus, a gram-positive facultative anaerobe, is one of the most important lactic acid bacteria widely used in the dairy fermentation industry. In this study, we have analyzed the global transcriptional profiling of S. thermophilus upon temperature change. During a temperature shift from 42°C to 50°C, it is found that 196 (10.4%) genes show differential expression with 102 up-regulated and 94 down-regulated at 50°C. In particular, 1) Heat shock genes, such as DnaK, GroESL and clpL, are identified to be elevated at 50°C; 2) Transcriptional regulators, such as HrcA, CtsR, Fur, MarR and MerR family, are differentially expressed, indicating the complex molecular mechanisms of S. thermophilus adapting to heat shock; 3) Genes associated with signal transduction, cell wall genes, iron homeostasis, ABC transporters and restriction-modification system were induced; 4) A large number of the differentially expressed genes are hypothetical genes of unknown function, indicating that much remains to be investigated about the heat shock response of S. thermophilus. Experimental investigation of selected heat shock gene ClpL shows that it plays an important role in the physiology of S. thermophilus at high temperature and meanwhile we confirmed ClpL as a member of the CtsR regulon. Overall, this study has contributed to the underlying adaptive molecular mechanisms of S. thermophilus upon temperature change and provides a basis for future in-depth functional studies.
Highlights
Lactic acid bacteria play curial roles in the food industry since they are massively used for the manufacture of dairy products and fermentation processes [1]
To adapt to heat stress, bacteria up-regulated a number of heat shock genes, including chaperones encoded by the DnaK and GroE operons and ATPdependent proteases (Clp and Lon)
The molecular mechanisms underlying the heat shock responses have been investigated in many bacterial species, such as Listeria monocytogenes [9], Shewanella oneidensis [6] and Campylobacter jejuni [5]
Summary
Lactic acid bacteria play curial roles in the food industry since they are massively used for the manufacture of dairy products and fermentation processes [1]. Despite considerable efforts worldwide by scientist and food industry, the genetic and physiological stress response of S. thermophilus are still far from been studied [2,3]. Bacteria can monitor the environment and change their gene expression dynamically upon exposure to environmental factors, such as temperature, pH, osmotic activity, oxygen level and nutrient sources [4]. It is shown that bacteria can modify the expression of about 10% of their genes in response to an increase or decrease in growth temperature [5,6,7,8]. Despite the importance roles of S. thermophilus, little is known about its potential molecular mechanism in response to temperature changes. The transcriptome of mixed-culture growth of S. thermophilus and Lactobacillus has been investigated [11,12]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
