The Cold Shock Response of Lactobacillus casei: Relation between HPr Phosphorylation and Resistance to Freeze/Thaw Cycles

Rice bran as an encapsulating material to produce a healthy synbiotic product with improved gastrointestinal tolerance

To date, the coffee industry has the second highest market value in the world and consumer behavior has transitioned from drinking coffee just for its caffeine content to reduce sleepiness into an overall experience. Instant cold brew coffee in powder form can preserve the taste of coffee well; moreover, it is easy to transport. Several consumers have increasing interests in implementing lactic acid bacteria in healthy food due to their growing awareness of the probiotic's role. Several scholars have presented stress adaptation characteristics of single probiotic strains; however, comparisons of the stress-tolerant capacities of different probiotic strains are incomplete. Five lactic acid strains are tested for adaptation under four sublethal conditions. Lactobacillus casei is the most resilient probiotic in terms of heat and cold adaptation, while Lactobacillus acidophilus is more tolerant to low acid and bile salt; Then, these probiotics are subjected to a stress challenge that stimulates drying temperature, including a heat and cold stress challenge. The results show that acid adaptation can improve Lactobacillus acidophilus TISTR 1338 tolerance to harsh drying temperatures. In addition, encapsulation using prebiotic extracts from rice bran, with pectin and resistant starch combined through crosslinking and treated by freeze-drying, provides the highest encapsulation efficiency. In summary, acid-adapted L. acidophilus TISTR 1388 at the sublethal level can be applied to high and low temperature processing techniques. Additionally, the amount of viable probiotic after in vitro digestion remains at 5 log CFU/g, which is suitable for application in the production of synbiotic cold brew coffee.

Effects of oligosaccharides on the growth and stress tolerance of Lactobacillus plantarum ZLP001 in vitro, and the potential synbiotic effects of L. plantarum ZLP001 and fructo-oligosaccharide in post-weaning piglets1

In this study, we evaluated the effects of seven oligosaccharides on the growth rate and stress tolerance of Lactobacillus plantarum ZLP001 in vitro, and the potential synbiotic effects of the most effective oligosaccharide [fructo-oligosaccharide (FOS)] and L. plantarum ZLP001 on the growth performance, apparent nutrient digestibility, fecal microbiota, and serum immune index in weaning piglets. Most oligosaccharides were utilized as carbohydrate sources by L. plantarum ZLP001, but we observed obvious differences in the bacterial growth depending on oligosaccharide type and concentration. Oligosaccharides and glucose significantly alleviated the decrease in L. plantarum ZLP001 viability in artificial gastric fluid, whereas none of the sugars affected viability in artificial intestinal fluid. FOS and galacto-oligosaccharide significantly improved the viability of L. plantarum ZLP001 under heat stress (65 °C for 15 and 30 min). FOS and soybean oligosaccharide significantly increased the viability of L. plantarum ZLP001 in response to cold stress (4 °C for 30 and 60 days). On the basis of the findings of in vitro experiments, we selected FOS for in vivo studies. Eighty-four weaned piglets were randomly assigned to one of the following groups: control (basal diet, no additives), freeze-dried L. plantarum ZLP001 (4.2 × 109 CFU/g, 2 g/kg diet), FOS (5 g/kg diet), and combination (0.2% L. plantarum ZLP001 + 0.5% FOS). Body weight and feed consumption were recorded for determinations of the average daily gain (ADG), average daily feed intake (ADFI), and feed-to-gain ratio (F/G). On day 28, fresh fecal samples were collected to evaluate the apparent digestibility of nutrients and microbiota, and serum samples were collected to determine the immune status. L. plantarum ZLP001 plus FOS significantly increased ADG and decreased the F/G ratio compared with the no-additive control. The combination treatment also increased the apparent nutrient digestibility of dry matter and crude protein. Compared with the control and single supplementation, the combination treatment had a significant regulatory effect on the intestinal microbiota, as evidenced by increases in Lactobacillus spp. and a decrease in Enterobacteriaceae. In addition, the combination treatment increased the concentrations of serum IFN-γ and immunoglobulin G. In conclusion, FOS can be utilized well by L. plantarum ZLP001 and can be combined with it as a potential synbiotic that shows synergistic effects in weaning piglets.

The Lactobacillus casei Group: History and Health Related Applications

The Lactobacillus casei group (LCG), composed of the closely related Lactobacillus casei, Lactobacillus paracasei, and Lactobacillus rhamnosus are some of the most widely researched and applied probiotic species of lactobacilli. The three species have been extensively studied, classified and reclassified due to their health promoting properties. Differentiation is often difficult by conventional phenotypic and genotypic methods and therefore new methods are being continually developed to distinguish the three closely related species. The group remain of interest as probiotics, and their use is widespread in industry. Much research has focused in recent years on their application for health promotion in treatment or prevention of a number of diseases and disorders. The LCG have the potential to be used prophylactically or therapeutically in diseases associated with a disturbance to the gut microbiota. The group have been extensively researched with regard to stress responses, which are crucial for their survival and therefore application as probiotics.

New Genes Involved in Mild Stress Response Identified by Transposon Mutagenesis in Lactobacillus paracasei

Lactic acid bacteria (LAB) are associated with various plant, animal, and human niches and are also present in many fermented foods and beverages. Thus, they are subjected to several stress conditions and have developed advanced response mechanisms to resist, adapt, and grow. This work aimed to identify the genes involved in some stress adaptation mechanisms in LAB. For this purpose, global reverse genetics was applied by screening a library of 1287 Lactobacillus paracasei transposon mutants for mild monofactorial stresses. This library was submitted independently to heat (52°C, 30 min), ethanol (170 g.L⁻¹, 30 min), salt (NaCl 0.8 M, 24 h), acid (pH 4.5, 24 h), and oxidative (2 mM H₂O₂, 24 h) perturbations which trigger mild monofactorial stresses compatible with bacterial adaptation. Stress sensitivity of mutants was determined either by evaluating viability using propidium iodide (PI) staining, or by following growth inhibition through turbidity measurement. The screening for heat and ethanol stresses lead respectively to the identification of 63 and 27 genes/putative promoters whose disruption lead to an increased sensitivity. Among them, 14 genes or putative promoters were common for both stresses. For salt, acid and oxidative stresses, respectively 8, 6, and 9 genes or putative promoters were identified as essential for adaptation to these unfavorable conditions, with only three genes common to at least two stresses. Then, RT-qPCR was performed on selected stress response genes identified by mutant screenings in order to evaluate if their expression was modified in response to stresses in the parental strain. Eleven genes (membrane, transposase, chaperone, nucleotide and carbohydrate metabolism, and hypothetical protein genes) were upregulated during stress adaptation for at least two stresses. Seven genes, encoding membrane functions, were upregulated in response to a specific stress and thus could represent potential transcriptomic biomarkers. The results highlights that most of the genes identified by global reverse genetics are specifically required in response to one stress and that they are not differentially transcribed during stress in the parental strain. Most of these genes have not been characterized as stress response genes and provide new insights into the adaptation of lactic acid bacteria to their environment.

Stress responses in probiotic Lactobacillus casei

Survival in harsh environments is critical to both the industrial performance of lactic acid bacteria (LAB) and their competitiveness in complex microbial ecologies. Among the LAB, members of the Lactobacillus casei group have industrial applications as acid-producing starter cultures for milk fermentations and as specialty cultures for the intensification and acceleration of flavor development in certain bacterial-ripened cheese varieties. They are amongst the most common organisms in the gastrointestinal (GI) tract of humans and other animals, and have the potential to function as probiotics. Whether used in industrial or probiotic applications, environmental stresses will affect the physiological status and properties of cells, including altering their functionality and biochemistry. Understanding the mechanisms of how LAB cope with different environments is of great biotechnological importance, from both a fundamental and applied perspective: hence, interaction between these strains and their environment has gained increased interest in recent years. This paper presents an overview of the important features of stress responses in Lb. casei, and related proteomic or gene expression patterns that may improve their use as starter cultures and probiotics.

CspR, a cold shock RNA-binding protein involved in the long-term survival and the virulence of Enterococcus faecalis

By coprecipitation, we identified RNA-binding proteins in the Gram-positive opportunistic pathogen Enterococcus faecalis known to be deficient of the RNA chaperone Hfq. In particular, we characterized one belonging to the cold shock protein (Csp) family (Ef2925) renamed CspR for cold shock protein RNA binding. Compared to the wild-type strain, the ΔcspR mutant was less virulent in an insect infection model (Galleria mellonella) and exhibited a decreased persistence in mouse kidneys and a low survival rate in peritoneal macrophages. As expected, we found that the ΔcspR mutant strain was more impaired in its growth than the parental strain under cold conditions and in its long-term survival under nutrient starvation. All these phenotypes were restored after complementation of the ΔcspR mutant. In addition, Western blot analysis showed that CspR was overexpressed under cold shock conditions and in the stationary phase. Since CspR may act as an RNA chaperone, putative targets were identified using a global proteomic approach completed with transcriptomic assays. This study revealed that 19 proteins were differentially expressed in the ΔcspR strain (9 upregulated, 10 downregulated) and that CspR mainly acted at the posttranscriptional level. These data highlight for the first time the role of the RNA-binding protein CspR as a regulator in E. faecalis and its requirement in stress response and virulence in this important human pathogen.

Selection of low-temperature resistance in bacteria and potential applications

Microbial consortia may harbour an array of resistance mechanisms that facilitate survival under harsh conditions, including antifreeze and ice-nucleation proteins. Antifreeze proteins lower freezing points as well as inhibit the growth of large, potentially damaging ice crystals from small ice embryos. In contrast, ice-nucleation proteins prevent supercooling and allow ice formation at high, sub-zero temperatures. Psychrophiles and psychrotolerant microbes are typically sought in extremely cold environments. However, given that geography is unlikely to present an insurmountable barrier to microbial dispersal, we reasoned that species with low-temperature adaptations should also be present, although rare, in more temperate environments. In consequence, the challenge then becomes one of selecting for rare microbes present in a larger community. Following the introductory commentary, we demonstrate that both freeze-thaw survival and ice-affinity selection can be used to identify microbes, which demonstrate low-temperature resistance, from enrichments derived from temperate environments. Selection resulted in a drastic decrease in cell abundance and diversity, allowing the isolation of a subset of resistant microbes. Depending on the origin of the consortia, these resistant microbes demonstrated cross-tolerance to osmotic stress, or a high proportion of antifreeze and/or ice-nucleation protein activities. Both types of ice-associating proteins presumably facilitate microbial survival at low temperatures. These proteins, as well as molecules that maintain osmotic balance, are also of commercial interest, with applications in the food, energy and medical industries. In addition, the resistant phenotypes described here provide a glimpse into the breadth of strategies microbes use to survive and thrive at low temperatures.

The Phosphotransferase System of Lactobacillus casei: Regulation of Carbon Metabolism and Connection to Cold Shock Response

Genome sequencing of two different Lactobacillus casei strains (ATCC334 and BL23) is presently going on and preliminary data revealed that this lactic acid bacterium possesses numerous carbohydrate transport systems probably reflecting its capacity to proliferate under varying environmental conditions. Many carbohydrate transporters belong to the phosphoenolpyruvate:sugar phosphotransferase system (PTS), but all different kinds of non-PTS transporters are present as well and their substrates are known in a few cases. In L. casei regulation of carbohydrate transport and carbon metabolism is mainly achieved by PTS proteins. Carbon catabolite repression (CCR) is mediated via several mechanisms, including the major P-Ser-HPr/catabolite control protein A (CcpA)-dependent mechanism. Catabolite response elements, the target sites for the P-Ser-HPr/CcpA complex, precede numerous genes and operons. PTS regulation domain-containing antiterminators and transcription activators are also present in both L. casei strains. Their activity is usually controlled by two PTS-mediated phosphorylation reactions exerting antagonistic effects on the transcription regulators: P~EIIB-dependent phosphorylation regulates induction of the corresponding genes and P~His-HPr-mediated phosphorylation plays a role in CCR. Carbohydrate transport of L. casei is also regulated via inducer exclusion and inducer expulsion. The presence of glucose, fructose, etc. leads to inhibition of the transport or metabolism of less favorable carbon sources (inducer exclusion) or to the export of accumulated non-metabolizable carbon sources (inducer expulsion). While P-Ser-HPr is essential for inducer exclusion of maltose, it is not necessary for the expulsion of accumulated thio-methyl-beta-D-galactopyranoside. Surprisingly, recent evidence suggests that the PTS of L. casei also plays a role in cold shock response.