Expression of recombinant truncated domains of mucus-binding (Mub) protein of Lactobacillus plantarum in soluble and biologically active form

Host-microbe interaction and pathogen exclusion mediated by an aggregation-prone surface layer protein of Lactobacillus helveticus

Probiotic surface layer proteins (Slps) have multiple functions and bacterial adhesion to host cells is one of them. The precise role of Slps in cellular adhesion is not well understood due to its low native protein yield and self-aggregative nature. Here, we report the recombinant expression and purification of biologically active Slp of Lactobacillus helveticus NCDC 288 (SlpH) in high yield. SlpH is a highly basic protein (pI = 9.4), having a molecular weight of 45 kDa. Circular Dichroism showed a prevalence of beta-strands in SlpH structure and resistance to low pH. SlpH showed binding to human intestinal tissue, enteric Caco-2 cell line, and porcine gastric mucin, but not with fibronectin, collagen type IV and laminin. SlpH inhibited the binding of the enterotoxigenic E. coli by 70 % and 76 % and that of Salmonella Typhimurium SL1344 by 71 % and 75 % to enteric Caco-2 cell line in the exclusion and competition assays, respectively. The pathogen exclusion and competition activity and tolerance to harsh gastrointestinal conditions show the potential for developing SlpH as a prophylactic or therapeutic agent against enteric pathogens.

Molecular genetics for probiotic engineering: dissecting lactic acid bacteria

The composition of the gut microbiome is greatly influenced by nutrition and dietary alterations which can also induce large temporary microbial shifts. However, the molecular mechanisms that promote these changes remain to be determined. Species of the family Lactobacillaceae and Bacillus species are genetically manipulatable bacteria that are naturally found in the human gastrointestinal (GI) tract and are often considered models of beneficial microbiota. Here, we identify specific conserved molecular pathways that play a key role in host colonization by beneficial members of the microbiota. In particular, we highlight three pathways important to the success of lactic acid bacteria (LAB) in the GI tract: glycolysis and fermentation, microbial communication via membrane vesicles, and condition-dependent antibiotic production. We elaborate on how the understanding of these circuits can lead to the development of novel therapeutic approaches to combat GI tract infections.

The potential role of adherence factors in probiotic function in the gastrointestinal tract of adults and pediatrics: a narrative review of experimental and human studies

Numerous studies point to the important role of probiotic bacteria in gastrointestinal health. Probiotics act through mechanisms affecting enteric pathogens, epithelial barrier function, immune signaling, and conditioning of indigenous microbiota. Once administered, probiotics reach the gastrointestinal tract and interact with the host through bacterial surface molecules, here called adhesion factors, which are either strain- or specie-specific. Probiotic adhesion, through structural adhesion factors, is a mechanism that facilitates persistence within the gastrointestinal tract and triggers the initial host responses. Thus, an understanding of specific probiotic adhesion mechanisms could predict how specific probiotic strains elicit benefits and the potential of adherence factors as a proxy to predict probiotic function. This review summarizes the present understanding of probiotic adherence in the gastrointestinal tract. It highlights the bacterial adhesion structure types, their molecular communication with the host and the consequent impact on intestinal diseases in both adult and pediatric populations. Finally, we discuss knockout/isolation studies as direct evidence for adhesion factors conferring anti-inflammatory and pathogen inhibition properties to a probiotic.What is known: Probiotics can be used to treat clinical conditions.Probiotics improve dysbiosis and symptoms.Clinical trials may not confirm in vitro and animal studies.What is new: Adhesion structures may be important for probiotic function.Need to systematically determine physical characteristics of probiotics before selecting for clinical trials.Probiotics may be genetically engineered to add to clinical efficacy.

Recombinant expression and molecular characterization of buffalo sperm lysozyme-like protein 1

Several sperm lysozyme-like genes evolved from lysozyme by successive duplications and mutations; however their functional role in the reproduction of farm animals is not well understood. To understand the function and molecular properties of buffalo sperm lysozyme-like protein 1 (buSLLP1), it was expressed in E. coli; however, it partitioned to inclusion bodies. Lowering of temperature and inducer concentration did not help in the recovery of the expressed protein in the biologically active form. Therefore, buSLLP1 was cloned and expressed in Pichiapink system based on auxotrophic Pichia pastoris in a labscale fermenter. The expressed protein was obtained in flow-through by using a 30 kDa ultrafiltration membrane followed by MonoQ anion exchange chromatography, resulting in a homogenous preparation of 40 mg recombinant buSLLP1 per liter of initial spent culture-supernatant. Circular dichroism spectroscopy showed that recombinant buSLLP1 possessed a native-like secondary structure. The recombinant buSLLP1 also showed thermal denaturation profile typical of folded globular proteins; however, the thermal stability was lower than the hen egg white lysozyme. Binding of buSLLP1 to chitin and zona pellucida of buffalo oocytes showed that the recombinant buSLLP1 possessed a competent binding pocket, therefore, the produced protein could be used to study its functional role in the reproduction of farm animals.

Safety Evaluation and Whole-Genome Annotation of Lactobacillus plantarum Strains from Different Sources with Special Focus on Isolates from Green Tea

Lactobacillus plantarum shows high intraspecies diversity species, and has one of the largest genome sizes among the lactobacilli. It is adapted to diverse environments and provides a promising potential for various applications. The aim of the study was to investigate the safety and probiotic properties of 18 L. plantarum strains isolated from fermented food products, green tea, and insects. For preliminary safety evaluation the L. plantarum strains were tested for their ability to produce hemolysin and biogenic amines and for their antibiotic resistance. Based on preliminary safety screening, four strains isolated from green tea showed antibiotic resistance below the cut-off MIC values suggested by EFSA, and were selected out of the 18 strains for more detailed studies. Initial selection of strains with putative probiotic potential was determined by their capacity to survive in the human GIT using an in vitro simulation model, and for their adhesion to human Caco-2/TC-7 cell line. Under simulated GIT conditions, all four L. plantarum strains isolated from green tea showed higher survival rates than the control (L. plantarum subsp. plantarum ATCC 14917). All studied strains were genetically identified by 16S rRNA gene sequencing and confirmed to be L. plantarum. In addition, whole-genome sequence analysis of L. plantarum strains APsulloc 331261 and APsulloc 331263 from green tea was performed, and the outcome was compared with the genome of L. plantarum strain WCFS1. The genome was also annotated, and genes related to virulence factors were searched for. The results suggest that L. plantarum strains APsulloc 331261 and APsulloc 331263 can be considered as potential beneficial strains for human and animal applications.

Bio-therapeutics from human milk: prospects and perspectives

Human milk is elixir for neonates and is a rich source of nutrients and beneficial microbiota required for infant growth and development. Its benefits prompted research into probing the milk components and their use as prophylactic or therapeutic agents. Culture-independent estimation of milk microbiome and high-resolution identification of milk components provide information, but a holistic purview of these research domains is lacking. Here, we review the current research on bio-therapeutic components of milk and simplified future directions for its efficient usage. Publicly available databases such as PubMed and Google scholar were searched for keywords such as probiotics and prebiotics related to human milk, microbiome and milk oligosaccharides. This was further manually curated for inclusion and exclusion criteria relevant to human milk and clinical efficacy. The literature was classified into subgroups and then discussed in detail to facilitate understanding. Although milk research is still in infancy, it is clear that human milk has many functions including protection of infants by passive immunization through secreted antibodies, and transfer of immune regulators, cytokines and bioactive peptides. Unbiased estimates show that the human milk carries a complex community of microbiota which serves as the initial inoculum for establishment of infant gut. Our search effectively screened for evidence that shows that milk also harbours many types of prebiotics such as human milk oligosaccharides which encourage growth of beneficial probiotics. The milk also trains the naive immune system of the infant by supplying immune cells and stimulatory factors, thereby strengthening mucosal and systemic immune system. Our systematic review would improve understanding of human milk and the inherent complexity and diversity of human milk. The interrelated functional role of human milk components especially the oligosaccharides and microbiome has been discussed which plays important role in human health.

Experimental models to study intestinal microbes–mucus interactions in health and disease

A close symbiotic relationship exists between the intestinal microbiota and its host. A critical component of gut homeostasis is the presence of a mucus layer covering the gastrointestinal tract. Mucus is a viscoelastic gel at the interface between the luminal content and the host tissue that provides a habitat to the gut microbiota and protects the intestinal epithelium. The review starts by setting up the biological context underpinning the need for experimental models to study gut bacteria-mucus interactions in the digestive environment. We provide an overview of the structure and function of intestinal mucus and mucins, their interactions with intestinal bacteria (including commensal, probiotics and pathogenic microorganisms) and their role in modulating health and disease states. We then describe the characteristics and potentials of experimental models currently available to study the mechanisms underpinning the interaction of mucus with gut microbes, including in vitro, ex vivo and in vivo models. We then discuss the limitations and challenges facing this field of research.

Mechanistic insights into the host-microbe interaction and pathogen exclusion mediated by the Mucus-binding protein of Lactobacillus plantarum

Surface adhesins of pathogens and probiotics strains are implicated in mediating the binding of microbes to host. Mucus-binding protein (Mub) is unique to gut inhabiting lactic acid bacteria; however, the precise role of Mub proteins or its structural domains in host-microbial interaction is not well understood. Last two domains (Mubs5s6) of the six mucus-binding domains arranged in tandem at the C-terminus of the Lp_1643 protein of Lactobacillus plantarum was expressed in E. coli. Mubs5s6 showed binding with the rat intestinal mucus, pig gastric mucins and human intestinal tissues. Preincubation of Mubs5s6 with the Caco-2 and HT-29 cell lines inhibited the binding of pathogenic enterotoxigenic E. coli cells to the enterocytes by 68% and 81%, respectively. Pull-down assay suggested Mubs5s6 binding to the host mucosa components like cytokeratins, Hsp90 and Laminin. Mubs5s6 was predicted to possess calcium and glucose binding sites. Binding of Mubs5s6 with these ligands was also experimentally observed. These ligands are known to be associated with pathogenesis suggesting Mub might negotiate pathogens in multiple ways. To study the feasibility of Mubs5s6 delivery in the gut, it was encapsulated in chitosan-sodium tripolyphosphate microspheres with an efficiency of 65% and release up to 85% in near neutral pH zone over a period of 20 hours. Our results show that Mub plays an important role in the host-microbial cross-talk and possesses the potential for pathogen exclusion to a greater extent than mediated by L. plantarum cells. The functional and technological characteristics of Mubs5s6 make it suitable for breaking the host-pathogen interaction.

Expression of fibronectin-binding protein of L. acidophilus NCFM and in vitro refolding to adhesion capable native-like protein from inclusion bodies

The ability of Lactobacilli to adhere to host epithelial surface and intestinal tracts is important for colonization and persistence of bacteria in the host gut. Extracellular matrix components like fibronectin, mucin, collagen and other adhesion molecules serve as substratum for attachment of bacteria. However, the precise structure, function and mechanism of binding of microbial surface adhesion proteins such as Fibronectin-binding protein (FBP) with host molecules remains unclear. This is primarily due to limitations in high expression of these proteins in biologically active form. To study adhesion of its FBP (64 kDa), the fbp gene of L. acidophilus NCFM was cloned and expressed in E. coli. However, the fibronectin-binding protein expressed in soluble form could not be purified by Ni-NTA affinity chromatography possibly because of partially buried Histidine tag in the recombinant fusion protein. Therefore, the protein was expressed as inclusion bodies (IBs) at 37 °C and solubilized in urea followed by purification in denatured form by Ni-NTA affinity chromatography. The purified denatured protein was refolded in vitro to structurally stable and biologically active form. The conformational properties of the refolded protein were studied by circular dichroism, which showed prominence of α+ β structural element. The refolded FBP also showed significant binding to human intestinal tissue sections. Our optimized refolding protocol from IBs of this recombinant probiotic FBP led into high amounts of biologically active protein. Our results help in increasing understanding of structure-function relation of surface adhesion proteins and host-microbial interactions.