Proteomic analysis reveals the temperature-dependent presence of extracytoplasmic peptidases in the biofilm exoproteome
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Proteomic analysis reveals the temperature-dependent presence of extracytoplasmic peptidases in the biofilm exoproteome of Listeria monocytogenes EGD-e§ Yue-Jia Lee and Chinling Wang* Department of Basic Sciences, College of Veterinary Medicine, Mississippi State University, 240 Wise Center Drive, Mississippi 39762, USA (Received Nov 4, 2019 / Revised Jun 3, 2020 / Accepted Jun 15, 2020)
The foodborne pathogen Listeria monocytogenes resists environmental stresses by forming biofilms. Because this pathogen transmits between the environment and the host, it must adapt to temperature as an environmental stress. In this study, we aimed to identify which proteins were present depending on the temperature in the biofilms of L. monocytogenes EGD-e. Proteins in the supernatants of biofilms formed at 25°C and 37°C were compared using two-dimensional gel electrophoresis and liquid chromatography with tandem mass spectrometry. The larger number of extracytoplasmic proteins associated with cell wall/membrane/envelop biogenesis was identified from the supernatant of biofilms formed at 25°C (7) than those at 37°C (0). Among the 16 extracytoplasmic proteins detected only at 25°C, three were peptidases, namely Spl, Cwh, and Lmo0186. Moreover, mRNA expression of the three peptidases was higher at 25°C than at 37°C. Interestingly, this adaptation of gene expression to temperature was present in sessile cells but not in dispersed cells. After inhibiting the activity of extracytoplasmic peptidases with a protease inhibitor, we noted that the levels of biofilm biomass increased with higher concentrations of the protease inhibitor only when L. monocytogenes grew biofilms at 25°C and not at 37°C. Overall, our data suggest an effect of temperature on the presence of peptidases in L. monocytogenes biofilms. Additionally, increasing the levels of extracytoplasmic peptidases in biofilms is likely a unique feature for sessile L. monocytogenes that causes a naturally occurring breakdown of biofilms and facilitates the pathogen exiting biofilms and disseminating into the environment. Keywords: cell wall metabolism, extracytoplasmic peptidases, sessile mode, biofilm dispersion
*For correspondence. E-mail: [email protected]; Tel.: +1-662-325-1683; Fax: +1-662-325-1031 § Supplemental material for this article may be found at http://www.springerlink.com/content/120956. Copyright ⓒ 2020, The Microbiological Society of Korea
Introduction Listeriosis is a serious disease caused by ingesting food contaminated by Listeria monocytogenes. This disease causes 15–20% of annual food-related deaths worldwide and is especially dangerous for the elderly, fetuses, newborns, pregnant women, and immunocompromised patients (Scallan et al., 2011; European Food Safety Authority; European Centre for Disease Prevention and Control, 2016). L. monocytogenes can adhere to multiple abiotic surfaces (Beresford et al., 2001; Silva et al., 2008) and form biofilms, which leads to persistent contamination of ready-to-eat foods (Lee and Wang, 2
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