Influence of Culture Conditions and Medium Compositions on the Production of Bacteriocin-Like Inhibitory Substances by Lactococcus lactis Gh1

Improved production of RNA-inhibiting antimicrobial peptide by Bacillus licheniformis MCC 2514 facilitated by a genetic algorithm optimized medium

One of the significant challenges during the purification and characterization of antimicrobial peptides (AMPs) from Bacillus sp. is the interference of unutilized peptides from complex medium components during analytical procedures. In this study, a semi-synthetic medium was devised to overcome this challenge. Using a genetic algorithm, the production medium of AMP is optimized. The parent organism, Bacillus licheniformis MCC2514, produces AMP in very small quantities. This AMP is known to inhibit RNA biosynthesis. The findings revealed that lactose, NH4Cl and NaNO3 were crucial medium constituents for enhanced AMP synthesis. The potency of the AMP produced was studied using bacterium, Kocuria rhizophila ATCC 9341. The AMP produced from the optimized medium was eightfold higher than that produced from the unoptimized medium. Furthermore, activity was increased by 1.5-fold when cultivation conditions were standardized using the optimized medium. Later, AMP was produced in a 5 L bioreactor under controlled conditions, which led to similar results as those of shake-flask production. The mode of action of optimally produced AMP was confirmed to be inhibition of RNA biosynthesis. Here, we demonstrate that improved production of AMP is possible with the developed semi-synthetic medium recipe and could help further AMP production in an industrial setup.

Anti-Listerial Activity of Bacteriocin-like Inhibitory Substance Produced by Enterococcus lactis LBM BT2 Using Alternative Medium with Sugarcane Molasses

Listeria monocytogenes is a foodborne pathogen that contaminates food-processing environments and persists within biofilms on equipment, thus reaching final products by cross-contamination. With the growing demand for clean-label products, the search for natural antimicrobials as biopreservants, such as bacteriocins, has shown promising potential. In this context, this study aimed to evaluate the anti-listerial action of bacteriocins produced by Enterococcus lactis LBM BT2 in an alternative medium containing sugarcane molasses (SCM). Molecular analyses were carried out to characterize the strain, including the presence of bacteriocin-related genes. In the kinetic study on SCM medium E. lactis, LBM BT2 showed biomass and bacteriocin productions similar to those observed on a sucrose-based medium (control), highlighting the potential of the sugarcane molasses as a low-cost substrate. Stability tests revealed that the molecule remained active in wide ranges of pH (4-10) and temperature (60-100 °C). Furthermore, the proteolytic treatment reduced the biomolecule's antimicrobial activity, highlighting its proteinaceous nature. After primary purification by salting out and tangential flow filtration, the bacteriocin-like inhibitory substance (BLIS) showed bacteriostatic activity on suspended L. monocytogenes cells and against biofilm formation at a concentration of 0.625 mg/mL. These results demonstrate the potential of the produced BLIS as a biopreservative in the food industry.

Under conditions closely mimicking vaginal fluid, Lactobacillus jensenii strain 62B produces a bacteriocin-like inhibitory substance that targets and eliminates Gardnerella species

Within the vaginal ecosystem, lactobacilli and Gardnerella spp. likely interact and influence each other's growth, yet the details of this interaction are not clearly defined. Using medium simulating vaginal fluid and a two-chamber co-culturing system to prevent cell-to-cell contact between the bacteria, we examined the possibility that Lactobacillus jensenii 62B (Lj 62B) and/or G. piotii (Gp) JCP8151B produce extracellular factors through which they influence each other's viability. By 24 h post-inoculation (hpi) in the co-culture system and under conditions similar to the vaginal environment - pH 5.0, 37 °C, and 5% CO2, Lj 62B viability was not affected but Gp JCP8151B had been eliminated. Cell-free supernatant harvested from Lj 62B cultures (Lj-CFS) at 20 hpi, but not 16 hpi, also eliminated Gp JCP8151B growth. Neither lactic acid nor H2O2 production by Lj 62B was responsible for this effect. The Lj-CFS did not affect viability of three species of lactobacilli or eight species of Gram-positive and Gram-negative uropathogens but eliminated viability of eight different strains of Gardnerella spp. Activity of the inhibitory factor within Lj-CFS was abolished by protease treatment and reduced by heat treatment suggesting it is most likely a bacteriocin-like protein; fractionation revealed that the factor has a molecular weight within the 10-30 kDa range. These results suggest that, in medium mimicking vaginal fluid and growth conditions similar to the vaginal environment, Lj 62B produces a potential bacteriocin-like inhibitory substance (Lj-BLIS) that clearly targets Gardnerella spp. strains. Once fully characterized, Lj-BLIS may be a potential treatment for Gardnerella-related BV that does not alter the vaginal microflora.

Antimicrobial peptides from Bacillus spp. and strategies to enhance their yield

Antibiotic resistance is a growing concern that is affecting public health globally. The search for alternative antimicrobial agents has become increasingly important. Antimicrobial peptides (AMPs) produced by Bacillus spp. have emerged as a promising alternative to antibiotics, due to their broad-spectrum antimicrobial activity against resistant pathogens. In this review, we provide an overview of Bacillus-derived AMPs, including their classification into ribosomal (bacteriocins) and non-ribosomal peptides (lipopeptides and polyketides). Additionally, we delve into the molecular mechanisms of AMP production and describe the key biosynthetic gene clusters involved. Despite their potential, the low yield of AMPs produced under normal laboratory conditions remains a challenge to large-scale production. This review thus concludes with a comprehensive summary of recent studies aimed at enhancing the productivity of Bacillus-derived AMPs. In addition to medium optimization and genetic manipulation, various molecular strategies have been explored to increase the production of recombinant antimicrobial peptides (AMPs). These include the selection of appropriate expression systems, the engineering of expression promoters, and metabolic engineering. Bacillus-derived AMPs offer great potential as alternative antimicrobial agents, and this review provides valuable insights on the strategies to enhance their production yield, which may have significant implications for combating antibiotic resistance. KEY POINTS: • Bacillus-derived AMP is a potential alternative therapy for resistant pathogens • Bacillus produces two main classes of AMPs: ribosomal and non-ribosomal peptides • AMP yield can be enhanced using culture optimization and molecular approaches.

Metagenome-assembled genomes for biomarkers of bio-functionalities in Laal dahi, an Indian ethnic fermented milk product

Laal dahi is a sweetened and soft pudding-like fermented milk product of the Eastern regions of India, which has not been studied for its microbial community structures and health promoting functionality in terms of 'omics' approaches. We applied metagenomic and metagenomes-assembled genomes (MAGs) tools to decipher the biomarkers for genes encoding for different health promoting functionalities in laal dahi. Abundance of bacterial domains was observed with negligible presence of eukaryotes and viruses. Bacillota was the most abundant phylum with different bacterial species viz., Enterococcus italicus, Lactococcus raffinolactis, Lactobacillus helveticus, Bifidobacterium mongoliense, Hafnia alvei, Lactococcus lactis, Acetobacter okinawensis, Streptococcus thermophilus, Thermus thermophilus, Leuconostoc citreum, Leuconostoc pseudomesenteroides, Acetobacter orientalis, Lactobacillus gallinarum, Lactococcus chungangensis and Lactobacillus delbrueckii. Comparison of laal dahi microbiome with that of similar fermented milk products was also carried out after retrieving the metagenomic datasets from public databases. Significant abundance of Lb. helveticus, E. italicus, Lc. raffinolactis and Lc. lactis in laal dahi. Interestingly, Bifidobacterium mongoliense, Lb. gallinarum, Lc. chungangensis and Acetobacter okinawensis were only detected in laal dahi but Streptococcus infantarius, Lacticaseibacillus rhamnosus and Lb. johnsonii were absent. Reconstruction of putative single environment-specific genomes from metagenomes in addition to subsampling of the abundant species resulted in five high-quality MAGs identified as Lactobacillus delbrueckii, Lactobacillus helveticus, Lactococcus chungangensis, Lactococcus lactis and Streptococcus thermophilus. All MAGs showed the presence of various genes with several putative functions corresponding to different probiotic and prebiotic functions, short-chain fatty acids production, immunomodulation, antitumor genes, essential amino acid and vitamin biosynthesis. Genes for γ-Aminobutyric acid (GABA) production were only detected in MAG of Lactococcus lactis. Gene clusters for secondary metabolites (antimicrobial peptides) were detected in all MAGs except Lc. chungangensis. Additionally, detection of clustered regularly interspaced short palindromic repeats (CRISPR)-associated (Cas) elements was observed only in Lactobacillus delbrueckii and Streptococcus thermophilus. Annotation of several genes with potential health beneficial properties in all five MAGs may support the need to explore the culturability of these MAGs for future use in controlled fermentation of functional dairy products.

In Situ Inactivation of Selected Bacillus Strains in Brewer's Spent Grain during Fermentation by Lactococcus lactis ATCC 11454-The Possibility of Post-Production Residues Management

The safety and quality of post-production residues is essential before they can be reused. Both to explore the possibility of reuse as a fermentation medium and the context of pathogens' inactivation, the research aimed to characterize the fermentation system of L. lactis ATCC 11454 and brewer's spent grain, malt and barley, especially to in situ inactivation of selected Bacillus strains during the fermentation and storage. Barley products were milled, autoclaved, hydrated and fermented with L. lactis ATCC 11454. Then, the co-fermentation with Bacillus strains was carried out. The amount of polyphenols in the samples ranged from 483.5 to 718.4 ug GAE g^-1 and increased after 24 h fermentation with L. lactis ATCC 11454. The high viability of LAB in the fermented samples and after 7 days of storage at 4 °C (8 log CFU g^-1) indicates the high nutrients bioavailability during the storage. Also, this co-fermentation on different barley products indicated a high reduction level (2 to 4 logs) of Bacillus due to the biosuppression effect of the LAB strain in this fermentation system. Brewer's spent grain (BSG) fermented with L. lactis ATCC 25 11454 produces a highly effective cell-free supernatant (CFS) for suppressing Bacillus strains. This was evident in both the inhibition zone and fluorescence analysis of bacteria viability. In conclusion, the obtained results justify the use of brewer's spent grain in selected food products, increasing their safety and nutritional value. This finding is highly beneficial in the sustainable management of post-production residues when current waste material can still serve as a source of food.

Culture Age, Growth Medium, Ultrasound Amplitude, and Time of Exposure Influence the Kinetic Growth of Lactobacillus acidophilus

The growth pattern of probiotics can be modified by changing their nutritional factors and their physiological stage. Meanwhile, high intensity ultrasound (HIUS) can be employed to increase probiotics’ biomass. The one-factor-at-a-time (OFAT) approach was employed to investigate the influence of the growth medium (MRS broth, whole milk, and skim milk), culture age (1 day and 7 days old) and ultrasound parameters (time and amplitude) on the kinetic parameters of L. acidophilus. The oldest culture (7 days) had a greater lag phase and time to reach the end of the sigmoidal curve (Tmax) (p < 0.05) as well as a lower rate (maximum growth potential μmax) compared to the youngest culture (1 day). Regarding the growth medium, skim milk presented the greatest L. acidophilus counts (p < 0.05). Meanwhile, sonication times (60 and 90 s) change µmax and Tmax. When 30% amplitude was applied, a greater μmax and a smaller Tmax were observed (p < 0.05). It can be concluded that the growth medium, culture age, and ultrasound parameters (time and amplitude) influence the kinetic parameters of L. acidophilus. Results from this study could be used in the design and optimization of processes to improve the growth of the probiotic L. acidophilus at industrial scale.

Nutritional Supplementation with Amino Acids on Bacterial Cellulose Production by Komagataeibacter intermedius: Effect Analysis and Application of Response Surface Methodology

Bacterial cellulose (BC) is a biopolymer mainly produced by acetic acid bacteria (AAB) that has several applications in the medical, pharmaceutical, and food industries. As other living organisms, AAB require sources of chemical elements and nutrients, which are essential for their multiplication and metabolite production. So, the knowledge of the nutritional needs of microorganisms that have important industrial applications is necessary for the nutrients to be supplied in the appropriate form and amount. Considering that the choice of different nutrients as nitrogen source can result in different metabolic effects, this work aimed to verify the effects of amino acid supplementation in the culture media for BC production by an AAB strain (Komagataeibacter intermedius V-05). For this, nineteen amino acids were tested, selected, and optimized through a Plackett and Burman factorial design and central composite design to determine the optimal concentrations of each required amino acid. Membranes produced under optimal conditions were characterized in relation to chemical structure and properties by X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), infrared spectroscopy (FT-IR), and hydrophilic properties. Three amino acids had a significant positive effect and were required: aspartic acid (1.5 g L^-1), phenylalanine (1.5 g L^-1), and serine (3.0 g L^-1). Conversely, all sulfur and positively charged amino acids had a negative effect and reduced the production yield. After optimization and validation steps, a production level of 3.02 g L^-1 was achieved. Membranes produced from optimized media by this strain presented lower crystallinity index but greater thermal and hydrophilic properties than those produced from standard HS medium.

Biosynthesis and Production of Class II Bacteriocins of Food-Associated Lactic Acid Bacteria

Bacteriocins are ribosomally synthesized peptides made by bacteria that inhibit the growth of similar or closely related bacterial strains. Class II bacteriocins are a class of bacteriocins that are heat-resistant and do not undergo extensive posttranslational modification. In lactic acid bacteria (LAB), class II bacteriocins are widely distributed, and some of them have been successfully applied as food preservatives or antibiotic alternatives. Class II bacteriocins can be further divided into four subcategories. In the same subcategory, variations were observed in terms of amino acid identity, peptide length, pI, etc. The production of class II bacteriocin is controlled by a dedicated gene cluster located in the plasmid or chromosome. Besides the pre-bacteriocin encoding gene, the gene cluster generally includes various combinations of immunity, transportation, and regulatory genes. Among class II bacteriocin-producing LAB, some strains/species showed low yield. A multitude of fermentation factors including medium composition, temperature, and pH have a strong influence on bacteriocin production which is usually strain-specific. Consequently, scientists are motivated to develop high-yielding strains through the genetic engineering approach. Thus, this review aims to present and discuss the distribution, sequence characteristics, as well as biosynthesis of class II bacteriocins of LAB. Moreover, the integration of modern biotechnology and genetics with conventional fermentation technology to improve bacteriocin production will also be discussed in this review.

Microbial Secondary Metabolism and Biotechnology

In recent decades scientific research has demonstrated that the microbial world is infinitely richer and more surprising than we could have imagined. Every day, new molecules produced by microorganisms are discovered, and their incredible diversity has not yet delivered all of its messages. The current challenge of research is to select from the wide variety of characterized microorganisms and compounds, those which could provide rapid answers to crucial questions about human or animal health or more generally relating to society’s demands for medicine, pharmacology, nutrition or everyday well-being.

Extractive Fermentation for Recovery of Bacteriocin-Like Inhibitory Substances Derived from Lactococcus lactis Gh1 Using PEG2000/Dextran T500 Aqueous Two-Phase System

This work aimed to optimize the parameters affecting partitioning of a bacteriocin-like inhibitory substances (BLIS) from Lactococcus lactis Gh1 in extractive fermentation using polyethylene glycol (PEG)/dextran aqueous two-phase system (ATPS). This system was developed for the simultaneous cell cultivation and downstream processing of BLIS. Results showed that the molecular weight of PEG, PEG concentration, and dextran T500 affect the partition coefficient (K), purification factor (PF), and yield of BLIS partitioning. ATPS composed of 10% (w/w) PEG2000 and 8% (w/w) dextran T500, provided the greatest conditions for the extractive BLIS production. The K (1.00 ± 0.16), PF (2.92 ± 0.37) and yield (77.24 ± 2.81%) were increased at selected orbital speed (200 rpm) and pH (pH 7). Sustainable growth of the cells in the bioreactor and repeated fermentation up to the eighth extractive batch were observed during the scale up process, ensuring a continuous production and purification of BLIS. Hence, the simplicity and effectiveness of ATPS in the purification of BLIS were proven in this study.

Evaluation of the Estimation Capability of Response Surface Methodology and Artificial Neural Network for the Optimization of Bacteriocin-Like Inhibitory Substances Production by Lactococcus lactis Gh1

Bacteriocin-like inhibitory substances (BLIS) produced by Lactococcus lactis Gh1 had shown antimicrobial activity against Listeria monocytogenes ATCC 15313. Brain Heart Infusion (BHI) broth is used for the cultivation and enumeration of lactic acid bacteria, but there is a need to improve the current medium composition for enhancement of BLIS production, and one of the approaches is to model the optimization process and identify the most appropriate medium formulation. Response surface methodology (RSM) and artificial neural network (ANN) models were employed in this study. In medium optimization, ANN (R² = 0.98) methodology provided better estimation point and data fitting as compared to RSM (R² = 0.79). In ANN, the optimal medium consisted of 35.38 g/L soytone, 16 g/L fructose, 3.25 g/L sodium chloride (NaCl) and 5.40 g/L disodium phosphate (Na₂HPO₄). BLIS production in optimal medium (717.13 ± 0.76 AU/mL) was about 1.40-fold higher than that obtained in nonoptimised (520.56 ± 3.37 AU/mL) medium. BLIS production was further improved by about 1.18 times higher in 2 L stirred tank bioreactor (787.40 ± 1.30 AU/mL) as compared to that obtained in 250 mL shake flask (665.28 ± 14.22 AU/mL) using the optimised medium.