Serial cultures in invert emulsion and monophase systems for microbial community shaping and propagation.

BACKGROUND: Microbial communities harbor important biotechnological potential in diverse domains, however, the engineering and propagation of such communities still face both knowledge and know-how gaps. More specifically, culturing tools are needed to propagate and shape microbial communities, to obtain desired properties, and to exploit them. Previous work suggested that micro-confinement and segregation of microorganisms using invert (water-in-oil, w/o) emulsion broth can shape communities during propagation, by alleviating biotic interactions and inducing physiological changes in cultured bacteria. The present work aimed at evaluating invert emulsion and simple broth monophasic cultures for the propagation and shaping of bacterial communities derived from raw milk in a serial propagation design. RESULTS: The monophasic setup resulted in stable community structures during serial propagation, whereas the invert emulsion system resulted in only transiently stable structures. In addition, different communities with different taxonomic compositions could be obtained from a single inoculum. Furthermore, the implementation of invert emulsion systems has allowed for the enrichment of less abundant microorganisms and consequently facilitated their isolation on culture agar plates. CONCLUSIONS: The monophasic system enables communities to be propagated in a stable manner, whereas the invert emulsion system allowed for the isolation of less abundant microorganisms and the generation of diverse taxonomic compositions from a single inoculum.

Invert emulsions alleviate biotic interactions in bacterial mixed culture.

The large application potential of microbiomes has led to a great need for mixed culture methods. However, microbial interactions can compromise the maintenance of biodiversity during cultivation in a reactor. In particular, competition among species can lead to a strong disequilibrium in favor of the fittest microorganism. In this study, an invert emulsion system was designed by dispersing culture medium in a mixture of sunflower oil and the surfactant PGPR. Confocal laser scanning microscopy revealed that this system allowed to segregate microorganisms in independent droplets. Granulomorphometric analysis showed that the invert emulsion remains stable during at least 24 h, and that the introduction of bacteria did not have a significant impact on the structure of the invert emulsion. A two-strain antagonistic model demonstrated that this invert emulsion system allows the propagation of two strains without the exclusion of the less-fit bacterium. The monitoring of single-strain cultures of bacteria representative of a cheese microbiota revealed that all but Brevibacterium linens were able to grow. A consortium consisting of Lactococcus lactis subsp. lactis biovar diacetylactis, Streptococcus thermophilus, Leuconostoc mesenteroides, Staphylococcus xylosus, Lactiplantibacillus plantarum and Carnobacterium maltaromaticum was successfully cultivated without detectable biotic interactions. Metabarcoding analysis revealed that the system allowed a better maintenance of alpha diversity and produced a propagated bacterial consortium characterized by a structure closer to the initial state compared to non-emulsified medium. This culture system could be an important tool in the field of microbial community engineering.

Genes associated to lactose metabolism illustrate the high diversity of Carnobacterium maltaromaticum.

The dairy population of Carnobacterium maltaromaticum is characterized by a high diversity suggesting a high diversity of the genetic traits linked to the dairy process. As lactose is the main carbon source in milk, the genetics of lactose metabolism was investigated in this LAB. Comparative genomic analysis revealed that the species C. maltaromaticum exhibits genes related to the Leloir and the tagatose-6-phosphate (Tagatose-6P) pathways. More precisely, strains can bear genes related to one or both pathways and several strains apparently do not contain homologs related to these pathways. Analysis at the population scale revealed that the Tagatose-6P and the Leloir encoding genes are disseminated in multiple phylogenetic lineages of C. maltaromaticum: genes of the Tagatose-6P pathway are present in the lineages I, II and III, and genes of the Leloir pathway are present in the lineages I, III and IV. These data suggest that these genes evolved thanks to horizontal transfer, genetic duplication and translocation. We hypothesize that the lac and gal genes evolved in C. maltaromaticum according to a complex scenario that mirrors the high population diversity.

Purification and characterization of halo-alkali-thermophilic protease from Halobacterium sp. strain HP25 isolated from raw salt, Lake Qarun, Fayoum, Egypt.

A total of 33 halophilic protease producers were isolated from different salt samples collected from Emisal salt company at Lake Qarun, Fayoum, Egypt. Of these strains, an extremely halophilic strain that grew optimally at 30 % (w/v) NaCl was characterized and identified as Halobacterium sp. strain HP25 based on 16S rRNA gene sequencing and phenotypic characterization. A halo-alkali-thermophilic protease was purified in three successive steps from the culture supernatant. The purified halophilic protease consisted of a single polypeptide chain with a molecular mass of 21 kDa and was enriched 167-fold to a specific activity of 6350 U mg(-1). The purified enzyme was active over a broad pH range from 6.0 to 11.0, with maximum activity at pH 8.0, exhibited a broad temperature range from 30 to 80 °C with optimum activity at 60 °C, and was active at salt concentrations ranging from 5 to 25 % (w/v), with optimum activity at 17 % NaCl (w/v). The K M and V max values of the purified halophilic protease with casein as a substrate were 523 µg mL(-1) and 2500 µg min(-1) mL(-1), respectively. In addition, this enzyme was stable in the tested organic solvents and laundry detergents such methanol, propanol, butanol, hexane, Persil and Ariel. The unusual properties of this enzyme allow it to be used for various applications, such as the ripening of salted fish. Furthermore, its stability and activity in the presence of organic solvents and detergents also allow the use of this enzyme for further novel applications and as an additive in detergent formulations.

High genetic diversity among strains of the unindustrialized lactic acid bacterium Carnobacterium maltaromaticum in dairy products as revealed by multilocus sequence typing.

Dairy products are colonized with three main classes of lactic acid bacteria (LAB): opportunistic bacteria, traditional starters, and industrial starters. Most of the population structure studies were previously performed with LAB species belonging to these three classes and give interesting knowledge about the population structure of LAB at the stage where they are already industrialized. However, these studies give little information about the population structure of LAB prior their use as an industrial starter. Carnobacterium maltaromaticum is a LAB colonizing diverse environments, including dairy products. Since this bacterium was discovered relatively recently, it is not yet commercialized as an industrial starter, which makes C. maltaromaticum an interesting model for the study of unindustrialized LAB population structure in dairy products. A multilocus sequence typing scheme based on an analysis of fragments of the genes dapE, ddlA, glpQ, ilvE, pyc, pyrE, and leuS was applied to a collection of 47 strains, including 28 strains isolated from dairy products. The scheme allowed detecting 36 sequence types with a discriminatory index of 0.98. The whole population was clustered in four deeply branched lineages, in which the dairy strains were spread. Moreover, the dairy strains could exhibit a high diversity within these lineages, leading to an overall dairy population with a diversity level as high as that of the nondairy population. These results are in agreement with the hypothesis according to which the industrialization of LAB leads to a diversity reduction in dairy products.

Serial fermentation in milk generates functionally diverse community lineages with different degrees of structure stabilization.

Microbial communities offer considerable potential for tackling environmental challenges by improving the functioning of ecosystems. Top-down community engineering is a promising strategy that could be used to obtain communities of desired function. However, the ecological factors that control the balance between community shaping and propagation are not well understood. Dairy backslopping, which consists of using part of the previous production to inoculate a new one, can be used as a model engineering approach to investigate community dynamics during serial propagations. In this study, 26 raw milk samples were serially propagated 6 times each, giving rise to 26 community lineages. Bacterial community structures were analyzed by metabarcoding, and acidification was recorded by pH monitoring. The results revealed that different types of community lineages could be obtained in terms of taxonomic composition and dynamics. Five lineages reached a repeatable community structure in a few propagation steps, with little variation between the final generations, giving rise to stable acidification kinetics. Moreover, these stabilized communities presented a high variability of structure and diverse acidification properties between community lineages. Besides, the other lineages were characterized by different levels of dynamics leading to parallel or divergent trajectories. The functional properties and dynamics of the communities were mainly related to the relative abundance and the taxonomic composition of lactic acid bacteria within the communities. These findings highlight that short-term schemes of serial fermentation can produce communities with a wide range of dynamics and that the balance between community shaping and propagation is intimately linked to community structure. IMPORTANCE: Microbiome applications require approaches for shaping and propagating microbial communities. Shaping allows the selection of communities with desired taxonomic and functional properties, while propagation allows the production of the biomass required to inoculate the engineered communities in the target ecosystem. In top-down community engineering, where communities are obtained from a pool of mixed microorganisms by acting on environmental variables, a major challenge is to master the balance between shaping and propagation. However, the ecological factors that favor high dynamics of community structure and, conversely, those that favor stability during propagation are not well understood. In this work, short-term dairy backslopping was used to investigate the key role of the taxonomic composition and structure of bacterial communities on their dynamics. The results obtained open up interesting prospects for the biotechnological use of microbiomes, particularly in the field of dairy fermentation, to diversify approaches for injecting microbial biodiversity into cheesemaking processes.

A selection process based on the robustness of anti-Listeria monocytogenes activity reveals two strains of Carnobacterium maltaromaticum with biopreservation properties in cheese.

Biopreservation is an approach consisting of using microorganisms as protective cultures and/or their metabolites to optimize the microbiological quality and shelf life of food by ensuring safety or reducing food waste. Biopreservation strain selection pipelines mainly focus on inhibition strength to identify strains of interest. However, in addition to inhibition strength, inhibition activity must be able to be expressed despite significant variations in food matrix properties. In this study, the anti-Listeria monocytogenes EGDelux properties of a collection of 77 Carnobacterium maltaromaticum strains were investigated by high throughput competition assays under varying conditions of co-culture inoculation level, time interval between inoculation with C. maltaromaticum and L. monocytogenes, pH, and NaCl, resulting in 1309 different combinations of C. maltaromaticum strains and culture conditions. This screening led to the selection of two candidate strains with potent and robust anti-L. monocytogenes activities. Deferred growth inhibition assays followed by halo measurements, and liquid co-culture followed by colony counting, revealed that these two strains exhibit a wide anti-Listeria spectrum. Challenge tests in Camembert and Saint-Nectaire cheese revealed both strains were able to inhibit a cocktail of five strains of L. monocytogenes with high potency and high reproducibility. These results highlight the importance of including the robustness criterion in addition to potency when designing a strain selection process for biopreservation applications.

Deciphering Rind Color Heterogeneity of Smear-Ripened Munster Cheese and Its Association with Microbiota.

Color is one of the first criteria to assess the quality of cheese. However, very limited data are available on the color heterogeneity of the rind and its relationship with microbial community structure. In this study, the color of a wide range of smear-ripened Munster cheeses from various origins was monitored during storage by photographic imaging and data analysis in the CIELAB color space using luminance, chroma, and hue angle as descriptors. Different levels of inter- and intra-cheese heterogeneity were observed. The most heterogeneous Munster cheeses were the darkest with orange-red colors. The most homogeneous were the brightest with yellow-orange. K-means clustering revealed three clusters distinguished by their color heterogeneity. Color analysis coupled with metabarcoding showed that rinds with heterogeneous color exhibited higher microbial diversity associated with important changes in their microbial community structure during storage. In addition, intra-cheese community structure fluctuations were associated with heterogeneity in rind color. The species Glutamicibacter arilaitensis and Psychrobacter nivimaris/piscatorii were found to be positively associated with the presence of undesirable brown patches. This study highlights the close relationship between the heterogeneity of the cheese rind and its microbiota.

Characterization of Carnobacterium maltaromaticum LMA 28 for its positive technological role in soft cheese making.

Carnobacterium maltaromaticum is a lactic acid bacterium isolated from soft cheese. The objective of this work was to study its potential positive impact when used in cheese technology. Phenotypic and genotypic characterization of six strains of C. maltaromaticum showed that they belong to different phylogenetic groups. Although these strains lacked the ability to coagulate milk quickly, they were acidotolerant. They did not affect the coagulation capacity of starter lactic acid bacteria, Lactococcus lactis and Streptococcus thermophilus, used in dairy industry. The impact of C. maltaromaticum LMA 28 on bacterial flora of cheese revealed a significant decrease of Psychrobacter sp. concentration, which might be responsible for cheese aging phenomena. An experimental plan was carried out to unravel the mechanism of inhibition of Psychrobacter sp. and Listeria monocytogenes and possible interaction between various factors (cell concentration, NaCl, pH and incubation time). Cellular concentration of C. maltaromaticum LMA 28 was found to be the main factor involved in the inhibition of Psychrobacter sp. and L. monocytogenes.

Mining Biosynthetic Gene Clusters in Carnobacterium maltaromaticum by Interference Competition Network and Genome Analysis.

Carnobacterium maltaromaticum is a non-starter lactic acid bacterium (LAB) of interest in the dairy industry for biopreservation. This study investigated the interference competition network and the specialized metabolites biosynthetic gene clusters (BGCs) content in this LAB in order to explore the relationship between the antimicrobial properties and the genome content. Network analysis revealed that the potency of inhibition tended to increase when the inhibition spectrum broadened, but also that several strains exhibited a high potency and narrow spectrum of inhibition. The C. maltaromaticum strains with potent anti-L. monocytogenes were characterized by high potency and a wide intraspecific spectrum. Genome mining of 29 strains revealed the presence of 12 bacteriocin BGCs: four of class I and eight of class II, among which seven belong to class IIa and one to class IIc. Overall, eight bacteriocins and one nonribosomal peptide synthetase and polyketide synthase (NRPS-PKS) BGCs were newly described. The comparison of the antimicrobial properties resulting from the analysis of the network and the BGC genome content allowed us to delineate candidate BGCs responsible for anti-L. monocytogenes and anti-C. maltaromaticum activity. However, it also highlighted that genome analysis is not suitable in the current state of the databases for the prediction of genes involved in the antimicrobial activity of strains with a narrow anti-C. maltaromaticum activity.

Identification of Potential Citrate Metabolism Pathways in Carnobacterium maltaromaticum.

In the present study, we describe the identification of potential citrate metabolism pathways for the lactic acid bacterium (LAB) Carnobacterium maltaromaticum. A phenotypic assay indicated that four of six C. maltaromaticum strains showed weak (Cm 6-1 and ATCC 35586) or even delayed (Cm 3-1 and Cm 5-1) citrate utilization activity. The remaining two strains, Cm 4-1 and Cm 1-2 gave negative results. Additional analysis showed no or very limited utilization of citrate in media containing 1% glucose and 22 or 30 mM citrate and inoculated with Cm 6-1 or ATCC 35586. Two potential pathways of citrate metabolism were identified by bioinformatics analyses in C. maltaromaticum including either oxaloacetate (pathway 1) or tricarboxylic compounds such as isocitrate and α-ketoglutarate (pathway 2) as intermediates. Genes encoding pathway 1 were present in two out of six strains while pathway 2 included genes present in all six strains. The two potential citrate metabolism pathways in C. maltaromaticum may potentially affect the sensory profiles of milk and soft cheeses subjected to growth with this species.

Active food packaging evolution: transformation from micro- to nanotechnology.

Predicting which attributes consumers are willing to pay extra for has become straightforward in recent years. The demands for the prime necessity of food of natural quality, elevated safety, minimally processed, ready-to-eat, and longer shelf-life have turned out to be matters of paramount importance. The increased awareness of environmental conservation and the escalating rate of foodborne illnesses have driven the food industry to implement a more innovative solution, i.e. bioactive packaging. Owing to nanotechnology application in eco-favorable coatings and encapsulation systems, the probabilities of enhancing food quality, safety, stability, and efficiency have been augmented. In this review article, the collective results highlight the food nanotechnology potentials with special focus on its application in active packaging, novel nano- and microencapsulation techniques, regulatory issues, and socio-ethical scepticism between nano-technophiles and nano-technophobes. No one has yet indicated the comparison of data concerning food nano- versus micro-technology; therefore noteworthy results of recent investigations are interpreted in the context of bioactive packaging. The next technological revolution in the domain of food science and nutrition would be the 3-BIOS concept enabling a controlled release of active agents through bioactive, biodegradable, and bionanocomposite combined strategy.

Carnobacterium maltaromaticum: identification, isolation tools, ecology and technological aspects in dairy products.

Carnobacterium species constitute a genus of Lactic Acid Bacteria (LAB) present in different ecological niches. The aim of this article is to summarize the knowledge about Carnobacterium maltaromaticum species at different microbiological levels such as taxonomy, isolation and identification, ecology, technological aspects and safety in dairy products. Works published during the last decade concerning C. maltaromaticum have shown that this non-starter LAB (NSLAB) could present major interests in dairy product technology. Four reasons can be mentioned: i) it can grow in milk during the ripening period with no competition with starter LAB, ii) this species synthesizes different flavouring compounds e.g., 3-methylbutanal, iii) it can inhibit the growth of foodborne pathogens as Listeria monocytogenes due to its ability to produce bacteriocins, iv) it has never been reported to be involved in human diseases as no cases of human infection have been directly linked to the consumption of dairy products containing this species.

Nested structure of intraspecific competition network in Carnobacterium maltaromaticum.

While competition targeting food-borne pathogens is being widely documented, few studies have focused on competition among non-pathogenic food bacteria. Carnobacterium maltaromaticum is a genetically diverse lactic acid bacterium known for comprising several bacteriocinogenic strains with bioprotective potentialities against the food-borne pathogen Listeria monocytogenes. The aim of our study is to examine the network properties of competition among a collection of 73 strains of C. maltaromaticum and to characterize their individual interaction potential. The performed high-throughput competition assays, investigating 5 329 pairwise interactions, showed that intraspecific competition was major in C. maltaromaticum with approximately 56% of the sender strains antagonizing at least one receiver strain. A high diversity of inhibitory and sensitivity spectra was identified along with a majority of narrow inhibitory as well as sensitivity spectra. Through network analysis approach, we determined the highly nested architecture of C. maltaromaticum competition network, thus showing that competition in this species is determined by both the spectrum width of the inhibitory activity of sender strains and the spectrum width of the sensitivity of receiver strains. This study provides knowledge of the competition network in C. maltaromaticum that could be used in rational assembly of compatible microbial strains for the design of mixed starter cultures.

Bacterial diversity of Darfiyeh, a Lebanese artisanal raw goat's milk cheese.

In order to contribute to the preservation of the Lebanese dairy heritage, the aim of this study was to characterize the Darfiyeh cheese, a traditional variety made from raw goat's milk and ripened in goat's skin. Three independent batches of Darfiyeh production were analyzed after 20, 40 and 60 days of ripening. Mesophilic lactobacilli, thermophilic coccal-shaped lactic acid bacteria (LAB) and thermophilic lactobacilli were enumerated. In order to explore the Darfiyeh natural ecosystem, a combination of phenotypical and molecular approaches was applied. The latter included Polymerase Chain Reaction-temporal temperature gel electrophoresis (PCR-TTGE), classical PCR and quantitative PCR. These methods revealed the presence of Streptococcus thermophilus, Enterococcus faecium, Enterococcus durans, Enterococcus faecalis, Enterococcus malodoratus, group D Streptococcus sp., Lactococcus lactis subsp. lactis and L. lactis subsp. cremoris, Lactobacillus plantarum, Lactobacillus curvatus, Staphylococcus haemolyticus, Escherichia coli, Clostridium sp./Eubacterium tenue. Real-time PCR enabled quantification of E. faecium, with a detection of 10(7)-10(9) cfu g(-1) of product. The present molecular approaches combined with phenotypic method allowed describing the complex natural ecosystem of Darfiyeh, giving useful information for the preservation of Lebanese artisanal dairy products.

Functional differences in Leuconostoc sensitive and resistant strains to mesenterocin 52A, a class IIa bacteriocin.

Mesenterocin 52A (Mes 52A) is a class IIa bacteriocin produced by Leuconostoc mesenteroides ssp. mesenteroides FR52. The interaction of Mes 52A with bacterial membranes of sensitive, resistant and insensitive Leuconostoc strains has been investigated. The degree of insertion of Mes 52A on the phospholipid bilayer was studied by fluorescence anisotropy measurements using two probes, 1-(4-trimethylammonium)-6-phenyl-1,3,5-hexatriene (TMA-DPH) and DPH, located at different positions in the membrane, and the consequence for K(+) efflux and proton motive force was analyzed. Mes 52A caused an increase in the fluorescence of TMA-DPH and DPH in the membrane of the sensitive strain L. mesenteroides ssp. mesenteroides LMA 7, indicating that Mes 52A inserts into the cytoplasmic membrane of this sensitive strain. This insertion leads to K(+) efflux, without perturbation of DeltapH and a weak modification of DeltaPsi, and is consistent with pore formation. With the high-level resistant strain L. mesenteroides ssp. mesenteroides LMA 7AR, or with the insensitive strain Leuconostoc citreum CIP 103405, no modification of TMA-DPH or DPH anisotropy occurred, even in the presence of high Mes 52A levels. The membrane potential was not modified and no K(+) efflux was detected. There is a clear correlation between the physico-chemical characteristics of the membrane, the degree of Mes 52A penetration, the mechanism of action and the resistance or insensitivity characteristic of the target strains.

Optimization of the production and purification processes of carnobacteriocins Cbn BM1 and Cbn B2 from Carnobacterium maltaromaticum CP5 by heterologous expression in Escherichia coli.

An optimization of the production and purification processes of carnobacteriocins Cbn BM1 and Cbn B2 from Carnobacterium maltaromaticum CP5, by heterologous expression in Escherichia coli is described. The genes encoding mature bacteriocin were cloned into an E. coli expression system and expressed as a fusion protein with a thermostable thioredoxin. Recombinant E. coli were cultivated following a fed-batch fermentation process with pH, temperature and oxygenation regulation. The overexpression of the fusion proteins was improved by replacing IPTG by lactose. The fusion proteins were purified by thermal coagulation followed by affinity chromatography. The thioredoxin fusion protein was removed by using CNBr instead of enterokinase and the carnobacteriocins were recovered by reverse-phase chromatography. These optimizations led us to produce up to 320 mg of pure protein per liter of culture, which is four to ten fold higher than what is described for other heterologous expression systems.

Fluorescence anisotropy analysis of the mechanism of action of mesenterocin 52A: speculations on antimicrobial mechanism.

Mesenterocin 52A (Mes 52A) is a class IIa bacteriocin produced by Leuconostoc mesenteroides subsp. mesenteroides FR52, active against Listeria sp. The interaction of Mes 52A with bacterial membranes of two sensitive Listeria strains has been investigated. The Microbial Adhesion to Solvents test used to study the physico-chemical properties of the surface of the two strains indicated that both surfaces were rather hydrophilic and bipolar. The degree of insertion of Mes 52A in phospholipid bilayer was studied by fluorescence anisotropy measurements using two probes, 1-(4-trimethylammonium)-6-phenyl-1,3,5-hexatriene (TMA-DPH) and DPH, located at different positions in the membrane. TMA-DPH reflects the fluidity at the membrane surface and DPH of the heart. With Listeria ivanovii CIP 12510, Mes 52A induced an increase only in the TMA-DPH fluorescence anisotropy, indicating that this bacteriocin affects the membrane surface without penetration into the hydrophobic core of the membrane. No significant K(+) efflux was measured, whereas the Delta Psi component of the membrane potential was greatly affected. With Listeria innocua CIP 12511, Mes 52A caused an increase in the fluorescence of TMA-DPH and DPH, indicating that this peptide inserts deeply in the cytoplasmic membrane of this sensitive strain. This insertion led to K(+) efflux, without perturbation of Delta pH and a weak modification of Delta Psi, and is consistent with pore formation. These data indicate that Mes 52A interacts at different positions of the membrane, with or without pore formation, suggesting two different mechanisms of action for Mes 52A depending on the target strain.

High-Throughput Identification of Candidate Strains for Biopreservation by Using Bioluminescent Listeria monocytogenes.

This article describes a method for high-throughput competition assays using a bioluminescent strain of L. monocytogenes. This method is based on the use of the luminescent indicator strain L. monocytogenes EGDelux. The luminescence of this strain is correlated to growth, which make it suitable to monitor the growth of L. monocytogenes in mixed cultures. To this aim, luminescence kinetics were converted into a single numerical value, called the Luminescence Disturbance Indicator (LDI), which takes into account growth inhibition phenomena resulting in latency increase, decrease in the luminescence rate, or reduction of the maximum luminescence. The LDI allows to automatically and simultaneously handle multiple competition assays which are required for high-throughput screening (HTS) approaches. The method was applied to screen a collection of 1810 strains isolated from raw cow's milk in order to identify non-acidifying strains with anti-L. monocytogenes bioprotection properties. This method was also successfully used to identify anti-L. monocytogenes candidates within a collection of Lactococcus piscium, a species where antagonism was previously described as non-diffusible and requiring cell-to-cell contact. In conclusion, bioluminescent L. monocytogenes can be used in HTS to identify strains with anti-L. monocytogenes bioprotection properties, irrespectively of the inhibition mechanism.

Occurrence and Dynamism of Lactic Acid Bacteria in Distinct Ecological Niches: A Multifaceted Functional Health Perspective.

Lactic acid bacteria (LAB) are representative members of multiple ecosystems on earth, displaying dynamic interactions within animal and plant kingdoms in respect with other microbes. This highly heterogeneous phylogenetic group has coevolved with plants, invertebrates, and vertebrates, establishing either mutualism, symbiosis, commensalism, or even parasitism-like behavior with their hosts. Depending on their location and environment conditions, LAB can be dominant or sometimes in minority within ecosystems. Whatever their origins and relative abundance in specific anatomic sites, LAB exhibit multifaceted ecological and functional properties. While some resident LAB permanently inhabit distinct animal mucosal cavities, others are provided by food and may transiently occupy the gastrointestinal tract. It is admitted that the overall gut microbiome has a deep impact on health and diseases. Here, we examined the presence and the physiological role of LAB in the healthy human and several animal microbiome. Moreover, we also highlighted some dysbiotic states and related consequences for health, considering both the resident and the so-called "transionts" microorganisms. Whether LAB-related health effects act collectively or follow a strain-specificity dogma is also addressed. Besides the highly suggested contribution of LAB to interplay with immune, metabolic, and even brain-axis regulation, the possible involvement of LAB in xenobiotic detoxification processes and metal equilibrium is also tackled. Recent technological developments such as functional metagenomics, metabolomics, high-content screening and design in vitro and in vivo experimental models now open new horizons for LAB as markers applied for disease diagnosis, susceptibility, and follow-up. Moreover, identification of general and more specific molecular mechanisms based on antioxidant, antimicrobial, anti-inflammatory, and detoxifying properties of LAB currently extends their selection and promising use, either as probiotics, in traditional and functional foods, for dedicated treatments and mostly for maintenance of normobiosis and homeostasis.