Immunostimulatory Activity of Synbiotics Using Lactococcus lactis SG-030 and Glucooligosaccharides from Weissella cibaria YRK005

Much attention has been recently paid to the health benefits of synbiotics, a combination of probiotics and prebiotics. In this study, synbiotics were prepared by combining lactic acid bacteria with potential as probiotics and purified glucooligosaccharides, and their immunostimulatory activity was evaluated using RAW 264.7 macrophage cells. A lactic acid bacteria strain with high antioxidant activity, acid and bile salt tolerance, adhesion to Caco-2 cells, and nitric oxide (NO) production was selected as a potential probiotic strain. The selected strain, isolated from forsythia, was identified as Lactococcus lactis SG-030. The purified glucooligosaccharides produced from Weissella cibaria YRK005 were used as prebiotics. RAW 264.7 cells were treated with synbiotics in two ways. One way was a simultaneous treatment with lactic acid bacteria and glucooligosaccharides. The other way was to pre-culture the lactic acid bacteria with glucooligosaccharides followed by treatment with synbiotic culture broth or synbiotic culture supernatant. In both cases, synbiotics synergistically increased NO production in RAW 264.7 cells. In addition, synbiotics treatment increased the expression of tissue necrosis factor-α, interleukin (IL)-1β, IL-6, and inducible nitric oxide synthase genes. Synbiotics also increased the expression of P38, extracellular signal-regulated kinases, c-Jun N-terminal kinases, phosphoinositide 3-kinase, and Akt proteins. The results confirmed that the synbiotics prepared in this study exhibited synergistic immunostimulatory activity.

Contribution of influent rivers affected by different types of pollution to the changes of benthic microbial community structure in a large lake

As a microbial group in watershed ecosystems, the bacterial community is a sensitive indicator of external environmental fluctuations. However, the effects of different sources of exogenous pollution on the diversity and structure of bacterial communities in inflow rivers and lakes have not been studied in depth. In this study, we used 16S rRNA gene sequencing technology to study the diversity and composition of bacterial communities in rivers affected by different types of pollution. The results showed that the composition of the bacterial communities in rivers with different exogenous pollution sources was different. For example, the genus Arenimonas, which belongs to the Gamma-proteobacteria, is extensively enriched in IDPR (industrially and domestically polluted rivers) and ADPR (agriculturally and domestically polluted rivers) (KW, p < 0.05), while the genus Micromonospora is a more unique genus found in APR (agriculturally polluted rivers). When exploring the topology and classification characteristics of river microbial symbiosis models, it was found that the bacterial community symbiosis network is divided into six modules under different exogenous pollution regimes, and the nodes in the different modules perform different functions, such as the IDPR-dominated module I. In the network, the relatively abundant the genus Flavobacterium and the genus Nitrospira are the key factors driving the nitrogen cycle in the watershed where the samples were collected. In addition, our research indicates that communities in lake environments may be more susceptible to disturbances of various physiological or functional redundancies, thus retaining their original community structure. Overall, this study emphasizes that adaptive changes in the bacterial community structure of the sediments in the catchment and the occurrence of interactions are responses to different exogenous pollution sources.

Probiotic potential and biochemical and technological properties of Lactococcus lactis ssp. lactis strains isolated from raw milk and kefir grains

Lactococcus lactis ssp. lactis is one of the most important starter bacteria used in dairy technology and it is of great economic importance because of its use in the production of dairy products, including cheese, butter, cream, and fermented milks. Numerous studies have evaluated the biochemical and probiotic properties of lactococci; however, limited studies on the probiotic characteristics of lactococci were conducted using strains originating from raw milk and dairy products. Characterizing the probiotic properties of strains isolated from raw milk and fermented milk products is important in terms of selecting starter culture strains for the production of functional dairy products. In this study, biochemical properties (including antibiotic sensitivity, lipolytic activity, amino acid decarboxylation, antioxidant activity) and probiotic properties (including antimicrobial activity, growth in the presence of bile salts, bile salts deconjugation, and hydrophobicity) of 14 Lactococcus lactis strains isolated from raw milk and kefir grains were investigated. Strains originating from kefir grains had better characteristics in terms of antimicrobial activity and bile salt deconjugation, whereas strains from raw milk had better hydrophobicity and antioxidant activity characteristics. None of the strains were able to grow in the presence of bile salt and did not show amino acid decarboxylation or lipolytic activities. Biochemical and probiotic properties of L. lactis strains varied depending on the strain and some of these strains could be used as functional cultures depending on their properties. However, these strains did not possess all of the properties required to meet the definition of a probiotic.

Effect of proteolysis during Cheddar cheese aging on the detection of milk protein residues by ELISA

Cow milk is a common allergenic food, and cow milk-derived cheese retains an appreciable level of allergenicity. The specific and sensitive detection of milk protein residues in foods is needed to protect milk-allergic consumers from exposure to undeclared milk protein residues contained in foods made with milk or milk-derived ingredients or made on shared equipment or in shared facilities with milk or milk-derived ingredients. However, during cheese ripening, milk proteins are degraded by chymosin and milk-derived and bacterial proteases. Commercial allergen-detection methods are not validated for the detection of residues in fermented or hydrolyzed products. The objective of this research was to evaluate commercially available milk ELISA kits for their capability to detect milk protein residues in aged Cheddar cheese. Cheddar cheese was manufactured at a local dairy plant and was aged at 5°C for 24 mo, with samples removed at various time points throughout aging. Milk protein residues and protein profiles were measured using 4 commercial milk ELISA kits and sodium dodecyl sulfate-PAGE. The ELISA data revealed a 90% loss of milk protein residue signal between the youngest and oldest Cheddar cheese samples (0.5 and 24 mo, respectively). Sodium dodecyl sulfate-PAGE analysis showed protein degradation throughout aging, with the highest level of proteolysis observed at 24 mo. Results suggest that current commercial milk ELISA methods can detect milk protein residues in young Cheddar cheese, but the detection signal dramatically decreases during aging. The 4 evaluated ELISA kits were not capable of detecting trace levels of milk protein residues in aged cheese. Reliable detection of allergen residues in fermented food products is critical for upholding allergen-control programs, maintaining product safety, and protecting allergic consumers. Furthermore, this research suggests a novel use of ELISA kits to monitor protein degradation as an indication of cheese ripening.

Isolation, Identification, and Evaluation of New Lactic Acid Bacteria Strains with Both Cellular Antioxidant and Bile Salt Hydrolase Activities In Vitro

In this study, we analyzed Chinese traditional fermented food to isolate and identify new lactic acid bacteria (LAB) strains with novel functional properties and to evaluate their cellular antioxidant and bile salt hydrolase (BSH) activities in vitro. A sequential screening strategy was developed to efficiently isolate and obtain 261 LAB strains tolerant of bile salt, acid, and H₂O₂ from nine Chinese traditional fermented foods. Among these strains, 70 were identified as having 2,2-diphenyl-1-picrylhydrazyl radical scavenging and/or BSH activity. These strains belonged to eight species: Enterococcus faecium (33% of the strains), Lactobacillus plantarum (26%), Leuconostoc mesenteroides (14%), Pediococcus pentosaceus (6%), Enterococcus durans (9%), Lactobacillus brevis (9%), Pediococcus ethanolidurans (3%), and Lactobacillus casei (1%). The pulsed-field gel electrophoresis genome fingerprinting profiles of these strains revealed 38 distinct pulsotypes, indicating a high level of genomic diversity among the tested strains. Twenty strains were further evaluated for hydroxyl radical scavenging activity, reducing power, and ferrous ion chelating activity exerted by both viable intact cells and/or intracellular cell-free extracts. Some strains, such as L. plantarum D28 and E. faecium B28, had high levels of both cellular antioxidant and BSH activities in vitro. These strains are promising probiotic components for health-promoting functional foods.

Mesophilic Lactic Acid Bacteria Diversity Encountered in Brazilian Farms Producing Milk with Particular Interest in Lactococcus lactis Strains

The milk produced in regions with different traditions in Brazil is used for artisanal product production, which is characterized by different sensorial characteristics. This study aimed to identify the bacterial ecosystem of farms located in a traditional dairy region in the state of Minas Gerais and to characterize Lactococcus lactis strains, the species of interest in this study, using a multilocus sequence typing (MLST) protocol and pulsed-field gel electrophoresis (PFGE) technique. Samples were collected from raw milk and dairy environment from six farms. A total of 50 isolates were analyzed using 16S rRNA sequencing and species-specific PCR. Five genera were identified: Lactobacillus, Leuconostoc, Lactococcus, Enterococcus, and Staphylococcus, from ten different species. MLST (with six housekeeping genes) and PFGE (with SmaI endonuclease) were used for the characterization of 20 isolates of Lactococcus lactis from a dairy collection in this study. Both methods revealed a high clonal diversity of strains with a higher discriminatory level for PFGE (15 pulsotypes), compared to MLST (12 ST). This study contributes to the preservation of the Brazilian dairy heritage and provides insights into a part of the LAB population found in raw milk and dairy environment.

The Nanomechanical Properties of Lactococcus lactis Pili Are Conditioned by the Polymerized Backbone Pilin

Pili produced by Lactococcus lactis subsp. lactis are putative linear structures consisting of repetitive subunits of the major pilin PilB that forms the backbone, pilin PilA situated at the distal end of the pilus, and an anchoring pilin PilC that tethers the pilus to the peptidoglycan. We determined the nanomechanical properties of pili using optical-tweezers force spectroscopy. Single pili were exposed to optical forces that yielded force-versus-extension spectra fitted using the Worm-Like Chain model. Native pili subjected to a force of 0–200 pN exhibit an inextensible, but highly flexible ultrastructure, reflected by their short persistence length. We tested a panel of derived strains to understand the functional role of the different pilins. First, we found that both the major pilin PilB and sortase C organize the backbone into a full-length organelle and dictate the nanomechanical properties of the pili. Second, we found that both PilA tip pilin and PilC anchoring pilin were not essential for the nanomechanical properties of pili. However, PilC maintains the pilus on the bacterial surface and may play a crucial role in the adhesion- and biofilm-forming properties of L. lactis.

The carbohydrate metabolism signature of lactococcus lactis strain A12 reveals its sourdough ecosystem origin

Lactococcus lactis subsp. lactis strain A12 was isolated from sourdough. Combined genomic, transcriptomic, and phenotypic analyses were performed to understand its survival capacity in the complex sourdough ecosystem and its role in the microbial community. The genome sequence comparison of strain A12 with strain IL1403 (a derivative of an industrial dairy strain) revealed 78 strain-specific regions representing 23% of the total genome size. Most of the strain-specific genes were involved in carbohydrate metabolism and are potentially required for its persistence in sourdough. Phenotype microarray, growth tests, and analysis of glycoside hydrolase content showed that strain A12 fermented plant-derived carbohydrates, such as arabinose and α-galactosides. Strain A12 exhibited specific growth rates on raffinose that were as high as they were on glucose and was able to release sucrose and galactose outside the cell, providing soluble carbohydrates for sourdough microflora. Transcriptomic analysis identified genes specifically induced during growth on raffinose and arabinose and reveals an alternative pathway for raffinose assimilation to that used by other lactococci.

Relationships between fatty acid composition and bile tolerance in lactobacillus isolates from plants and from non-plant materials

Twenty plant-derived and 18 non-plant-derived strains of Lactobacillus casei were compared for their growth in tryptone – yeast extract – glucose broth containing 0.3% bile by measuring absorbance at a wavelength of 620 nm after 24 h of incubation at 37 °C. Bile tolerance — a fundamental probiotic property — was calculated by dividing the experimental data by control values (growth without bile). We found that bile tolerance was strain specific but that the average bile tolerance of the plant-derived strains was significantly (P < 0.05) lower than that of the non-plant-derived strains tested. All tested strains could not deconjugate sodium taurocholate, indicating that the difference in bile tolerance was not due to the ability to deconjugate bile. The fatty acid compositions of the test strains with and without exposure to 0.3% bile were investigated, and a statistical correlation analysis between these compositions and their bile tolerance was conducted. The fatty acids correlated with bile tolerance differed between plant and non-plant lactobacilli. This is the first report to show that the origin (i.e., growth environment) of lactobacilli affects their fatty acid composition, which in turn, appears to be related to their bile tolerance.