Differential Expression of Proteins inListeria monocytogenesUnder Thermotolerance-Inducing, Heat Shock, and Prolonged Heat Shock Conditions

Fate of osmotically adapted and biofilm Listeria monocytogenes cells after exposure to salt, heat, and liquid smoke, mimicking the stresses induced during the processing of hot smoked fish

The study aimed to investigate the response of osmotically adapted and detached biofilm Listeria monocytogenes cells following sequential stresses that occur during the processing of hot smoking, such as heating and smoke application. Thermal resistance of L. monocytogenes was significantly affected by previous osmotic adaptation of the cells. D60oC-values of osmotically adapted L. monocytogenes cells were significantly higher than control cells. The osmotically adapted and subsequently heat-injured cells were more resistant to PALCAM and less resistant to TSAYE with 5.00% NaCl (TSAYE/NaCl) than control cells. Detached biofilm cells were more thermotolerant and less resistant to PALCAM and TSAYE/NaCl than control cells. The sequential effect of smoking against heat-treated (60 °C, 20 min) and osmotically adapted or detached L. monocytogenes biofilm cells was investigated using two liquid smoke extracts (L9 and G6). L9 led to significantly higher reductions (>3.00-Log CFU) compared to G6. The heat-treated, detached biofilm cells revealed resistance to L9, presumably due to metabolic downregulation and physical protection by the extracellular polymeric substances (EPS). These data highlight the potential of the food industry to make informed decisions for using safe heat treatments during hot smoking to effectively inactivate L. monocytogenes and maintain rigorous environmental sanitation practices to control biofilm cells.

Survival strategies of Listeria monocytogenes to environmental hostile stress: biofilm formation and stress responses

Listeria monocytogenes is a critical foodborne pathogen that causes listeriosis and threatens public health. This pathogenic microorganism forms a transmission cycle in nature, food industry, and humans, expanding the areas of contamination among them and influencing food safety. L. monocytogenes forms biofilms to protect itself and promotes survival through stress responses to the various stresses (e.g., temperature, pH, and antimicrobial agents) that may be inflicted during food processing. Biofilms and mechanisms of resistance to hostile external or general stresses allow L. monocytogenes to survive despite a variety of efforts to ensure food safety. The current review article focuses on biofilm formation, resistance mechanisms through biofilms, and external specific or general stress responses of L. monocytogenes to help understand the unexpected survival rates of this bacterium; it also proposes the use of obstacle technology to effectively cope with it in the food industry.

Enhanced heat resistance of Listeria innocua as a surrogate of Listeria monocytogenes after sublethal heat treatment

Its ability to survive under different environmental conditions makes Listeria monocytogenes a critical concern for food safety. When the microorganisms are exposed to sublethal heat treatment above their optimum growth temperature, they increase stress adaptation for further heat treatments. In order to investigate heat stress resistance of L. monocytogenes, L. innocua as a surrogate was exposed to sublethal heat at 46 °C for 30 and 60 min, prior to heat treatment at 60 °C. There was no significant difference in D60°C values between samples exposed to sublethal heat for 30 min and non-pre-heat-treated samples (control) (P > 0.05). In comparison, sublethal heat treatment for 60 min caused a significant increase in D60°C values compared to control samples (P < 0.05). Additionally, cluster analysis of mass spectra obtained from MALDI-TOF was analysed by discriminant analysis of principal components (DAPC) for sublethal heat treatment at 46 °C for 30 min and control group to check stress response at the proteomic level. However, differentiation of stress responses by distinct clusters was not revealing.

Proteomic perspectives on thermotolerant microbes: an updated review

INTRODUCTION

Thermotolerant microbes are a group of microorganisms that survive in elevated temperatures. The thermotolerant microbes, which are found in geothermal heat zones, grow at temperatures of or above 45°C. The proteins present in such microbes are optimally active at these elevated temperatures. Hence, therefore, serves as an advantage in various biotechnological applications. In the last few years, scientists have tried to understand the molecular mechanisms behind the maintenance of the structural integrity of the cell and to study the stability of various thermotolerant proteins at extreme temperatures. Proteomic analysis is the solution for this search. Applying novel proteomic tools determines the proteins involved in the thermostability of microbes at elevated temperatures.

METHODS

Advanced proteomic techniques like Mass spectrometry, nano-LC-MS, protein microarray, ICAT, iTRAQ, and SILAC could enable the screening and identification of novel thermostable proteins.

RESULTS

This review provides up-to-date details on the protein signature of various thermotolerant microbes analyzed through advanced proteomic tools concerning relevant research articles. The protein complex composition from various thermotolerant microbes cultured at different temperatures, their structural arrangement, and functional efficiency of the protein was reviewed and reported.

CONCLUSION

This review provides an overview of thermotolerant microbes, their enzymes, and the proteomic tools implemented to characterize them. This article also reviewed a comprehensive view of the current proteomic approaches for protein profiling in thermotolerant microbes.

Proteomic Analysis of Listeria monocytogenes FBUNT During Biofilm Formation at 10°C in Response to Lactocin AL705

Listeria monocytogenes is one of the major food-related pathogens and is able to survive and multiply under different stress conditions. Its persistence in industrial premises and foods is partially due to its ability to form biofilm. Thus, as a natural strategy to overcome L. monocytogenes biofilm formation, the treatment with lactocin AL705 using a sublethal dose (20AU/ml) was explored. The effect of the presence of the bacteriocin on the biofilm formation at 10°C of L. monocytogenes FBUNT was evaluated for its proteome and compared to the proteomes of planktonic and sessile cells grown at 10°C in the absence of lactocin. Compared to planktonic cells, adaptation of sessile cells during cold stress involved protein abundance shifts associated with ribosomes function and biogenesis, cell membrane functionality, carbohydrate and amino acid metabolism, and transport. When sessile cells were treated with lactocin AL705, proteins’ up-regulation were mostly related to carbohydrate metabolism and nutrient transport in an attempt to compensate for impaired energy generation caused by bacteriocin interacting with the cytoplasmic membrane. Notably, transport systems such as β-glucosidase IIABC (lmo0027), cellobiose (lmo2763), and trehalose (lmo1255) specific PTS proteins were highly overexpressed. In addition, mannose (lmo0098), a specific PTS protein indicating the adaptive response of sessile cells to the bacteriocin, was downregulated as this PTS system acts as a class IIa bacteriocin receptor. A sublethal dose of lactocin AL705 was able to reduce the biofilm formation in L. monocytogenes FBUNT and this bacteriocin induced adaptation mechanisms in treated sessile cells. These results constitute valuable data related to specific proteins targeting the control of L. monocytogenes biofilm upon bacteriocin treatment.

Small RNAs as Fundamental Players in the Transference of Information During Bacterial Infectious Diseases

Communication shapes life on Earth. Transference of information has played a paramount role on the evolution of all living or extinct organisms since the appearance of life. Success or failure in this process will determine the prevalence or disappearance of a certain set of genes, the basis of Darwinian paradigm. Among different molecules used for transmission or reception of information, RNA plays a key role. For instance, the early precursors of life were information molecules based in primitive RNA forms. A growing field of research has focused on the contribution of small non-coding RNA forms due to its role on infectious diseases. These are short RNA species that carry out regulatory tasks in cis or trans. Small RNAs have shown their relevance in fine tuning the expression and activity of important regulators of essential genes for bacteria. Regulation of targets occurs through a plethora of mechanisms, including mRNA stabilization/destabilization, driving target mRNAs to degradation, or direct binding to regulatory proteins. Different studies have been conducted during the interplay of pathogenic bacteria with several hosts, including humans, animals, or plants. The sRNAs help the invader to quickly adapt to the change in environmental conditions when it enters in the host, or passes to a free state. The adaptation is achieved by direct targeting of the pathogen genes, or subversion of the host immune system. Pathogens trigger also an immune response in the host, which has been shown as well to be regulated by a wide range of sRNAs. This review focuses on the most recent host-pathogen interaction studies during bacterial infectious diseases, providing the perspective of the pathogen.

Comparative Whole Cell Proteomics of Listeria monocytogenes at Different Growth Temperatures

Listeria monocytogenes is a gram-positive, facultative anaerobe food pathogen responsible for the listeriosis that mostly occurs during the low-temperature storage of a cold cut or dairy products. To understand the systemic response to a wide range of growth temperatures, L. monocytogenes were cultivated at a different temperature from 10°C to 42°C, then whole cell proteomic analysis has been performed both exponential and stationary cells. The specific growth rate increased proportionally with the increase in growth temperature. The maximum growth rate was observed at 37°C and was maintained at 42°C. Global protein expression profiles mainly depended on the growth temperatures showing similar clusters between exponential and stationary phases. Expressed proteins were categorized by their belonging metabolic systems and then, evaluated the change of expression level in regard to the growth temperature and stages. DnaK, GroEL, GroES, GrpE, and CspB, which were the heat&cold shock response proteins, increased their expression with increasing the growth temperatures. In particular, GroES and CspB were expressed more than 100-fold than at low temperatures during the exponential phase. Meanwhile, CspL, another cold shock protein, overexpressed at a low temperature then exponentially decreased its expression to 65-folds. Chemotaxis protein CheV and flagella proteins were highly expressed at low temperatures and stationary phases. Housekeeping proteins maintained their expression levels constant regardless of growth temperature or growth phases. Most of the growth related proteins, which include central carbon catabolic enzymes, were highly expressed at 30°C then decreased sharply at high growth temperatures.

Impact of Combined Acidic and Hyperosmotic Shock Conditions on the Proteome ofListeria monocytogenesATCC 19115 in a Time-Course Study

Listeria monocytogenescan cause listeriosis in humans through consumption of contaminated food and can adapt to and grow under a wide array of physiochemical stresses. Consequently, it causes persistent food safety issues and requires vigilant sanitation processes to be in place, especially for the manufacture of high-risk food products. In this study, the global proteomic responses of the food-borne pathogenL. monocytogenesstrain ATCC 19115 were determined when exposed to nonthermal inactivation. This process was examined in the early stationary growth phase with the strain placed under simultaneous exposure to low pH (pH 3.5) and high salinity (aw0.900, 14% NaCl). Proteomic responses, measured using iTRAQ techniques, were conducted over a time course (5 min, 30 min, and 1 h at 25°C). The enumeration results showed that, at 5 min, cells underwent initial rapid inactivation by 1.2 log units and 2.5 log units after 30 min, and after that, culturability remained stable when sampled at 1 h. From the iTRAQ results, the proteome level changes that occur rapidly during the inactivation process mainly affected prophage, cell defense/detoxification, carbohydrate-related metabolism, transporter proteins, phosphotransferase systems, cell wall biogenesis, and specific cell surface proteins. Pathway map analysis revealed that several pathways are affected including pentose and glucuronate interconversions, glycolysis/gluconeogenesis, pyruvate metabolism, valine, leucine and isoleucine biosynthesis, oxidative phosphorylation, and proteins associated with bacterial invasion of epithelial cells and host survival. Proteome profiling provided a better understanding of the physiological responses of this pathogen to adapt to lethal nonthermal environments and indicates the need to improve food processing and storage methods, especially for non- or minimally thermally processed foods.

Listeriomics: an Interactive Web Platform for Systems Biology of Listeria

In the last decades, Listeria has become a key model organism for the study of host-pathogen interactions, noncoding RNA regulation, and bacterial adaptation to stress. To study these mechanisms, several genomics, transcriptomics, and proteomics data sets have been produced. We have developed Listeriomics, an interactive web platform to browse and correlate these heterogeneous sources of information. Our website will allow listeriologists and microbiologists to decipher key regulation mechanism by using a systems biology approach.

As for many model organisms, the amount of Listeria omics data produced has recently increased exponentially. There are now >80 published complete Listeria genomes, around 350 different transcriptomic data sets, and 25 proteomic data sets available. The analysis of these data sets through a systems biology approach and the generation of tools for biologists to browse these various data are a challenge for bioinformaticians. We have developed a web-based platform, named Listeriomics, that integrates different tools for omics data analyses, i.e., (i) an interactive genome viewer to display gene expression arrays, tiling arrays, and sequencing data sets along with proteomics and genomics data sets; (ii) an expression and protein atlas that connects every gene, small RNA, antisense RNA, or protein with the most relevant omics data; (iii) a specific tool for exploring protein conservation through the Listeria phylogenomic tree; and (iv) a coexpression network tool for the discovery of potential new regulations. Our platform integrates all the complete Listeria species genomes, transcriptomes, and proteomes published to date. This website allows navigation among all these data sets with enriched metadata in a user-friendly format and can be used as a central database for systems biology analysis.

IMPORTANCE In the last decades, Listeria has become a key model organism for the study of host-pathogen interactions, noncoding RNA regulation, and bacterial adaptation to stress. To study these mechanisms, several genomics, transcriptomics, and proteomics data sets have been produced. We have developed Listeriomics, an interactive web platform to browse and correlate these heterogeneous sources of information. Our website will allow listeriologists and microbiologists to decipher key regulation mechanism by using a systems biology approach.

Proteomics analysis of Listeria monocytogenes ATCC 19115 in response to simultaneous triple stresses

Listeria monocytogenes can cause listeriosis in humans through consumption of contaminated food. L. monocytogenes can adapt and grow in a vast array of physiochemical stresses in the food production environment. In this study, we performed a proteomics strategy in order to investigate how L. monocytogenes survives with a simultaneous exposure to low pH, high salinity and low temperature. The results showed that the adaptation processes mainly affected the biochemical pathways related to protein synthesis, oxidative stress, cell wall and nucleotide metabolism. Interestingly, enzymes involved in the carbohydrate metabolism of energy, such as glycolysis and pentose phosphate pathway, were derepressed due to the down-regulation of CodY, a global transcriptional repressor. The down-regulation of CodY, together with the up-regulation of carbohydrate metabolism enzymes, likely leads to the accumulation of pyruvate and further to the activation of fatty acid synthesis pathway. Proteomics profiling offered a better understanding of the physiological responses of this pathogen to adapt to harsh environment and would hopefully contribute to improving the food-processing and storage methods.

The contribution of transcriptomic and proteomic analysis in elucidating stress adaptation responses of Listeria monocytogenes

The foodborne transmission of Listeria monocytogenes requires physiological adaptation to various conditions, including the cold, osmotic, heat, acid, alkaline, and oxidative stresses, associated with food hygiene, processing, and preservation measures. We review the current knowledge on the molecular stress adaptation responses in L. monocytogenes cells as revealed through transcriptome, proteome, genetic, and physiological analysis. The adaptation of L. monocytogenes to stress exposure is achieved through global expression changes in a large number of cellular components. In addition, the cross-protection of L. monocytogenes exposed to different stress environments might be conferred through various cellular machineries that seem to be commonly activated by the different stresses. To assist in designing L. monocytogenes mitigation strategies for ready-to-eat food products, further experiments are warranted to specifically evaluate the effects of food composition, additives, preservatives, and processing technologies on the modulation of L. monocytogenes cellular components in response to specific stresses.

Proteomics for the elucidation of cold adaptation mechanisms in Listeria monocytogenes

Listeria monocytogenes, one of the major food-related pathogens, is the aetiological agent of listeriosis, a potentially life-threatening illness. It is able to survive in hostile environments and stress conditions such as those encountered in food-processing technologies (high salt concentration, wide range of pH and temperature, low water availability) and it also thrives at temperatures ranging from -0.4 to 45 °C. In this study, expression proteomics was applied to gain insight into key cellular events that allow L. monocytogenes to survive and multiply even at refrigeration temperatures. Interestingly, we observed that the adaptation processes mainly affect biochemical pathways related to protein synthesis and folding, nutrient uptake and oxidative stress. Furthermore, proteins implicated in metabolic pathways for energy production, such as glycolysis and Pta-AckA pathway, were present to a higher level in the cells grown at 4 °C. This suggests that, on the whole, cells exhibit an enhanced demand for energy to sustain cold growth. Proteomics may represent a key tool in deciphering specific mechanisms underlying cold adaptation response and, more widely, cell machinery.