Improving nitrogen source utilization from defatted soybean meal for nisin production by enhancing proteolytic function of Lactococcus lactis F44

Abstract

Nisin, one kind of natural antimicrobial peptide, is produced by certain Lactococcus lactis strains, which generally require expensive high-quality nitrogen sources due to limited ability of amino acids biosynthesis. Here we use defatted soybean meal (DSM) as sole nitrogen source to support L. lactis growth and nisin production. DSM medium composition and fermentation conditions were optimized using the methods of Plackett-Burman design and central composite design. The highest nisin production of 3879.58 IU/ml was obtained in DSM medium, which was 21.3% higher than that of commercial medium. To further increase the utilization ability of nitrogen sources, we enhanced the proteolytic function in L. lactis through rationally expressing the related enzymes, which were selected according to the compositions of amino acids and molecular weight of peptides in DSM medium. Significantly, an artificial proteolytic system consisting of a heterologous protease (NprB), an oligopeptides transporter subunit (OppA) and two peptidases (PepF and PepM) was introduced into L.lactis. The constructed strain BAFM was capable of achieving efficient biomass accumulation and nisin yield with 30% decreased amount of DSM hydrolysates, which further reduced the cost of nisin production. The strategy described here offers opportunities for low-cost L. lactis fermentation and large-scale nisin production in industry.

Quantitative proteomics of Lactococcus lactis F44 under cross-stress of low pH and lactate

“…On the other hand, OptA (oligopeptide ABC transporter substrate binding protein) was increased in L3P4 versus L3P7. Oligopeptides are taken up by a specific transport system and then internally hydrolysed by peptidases into AA (Liu et al, 2017). Overall, these results suggested an increased demand for a nitrogen source under cross-stress.…”

“…A total of 100 μL of diluted samples was spread on seed medium agar plates in triplicate and incubated at 30°C for 48 h. Cell survival numbers were estimated by calculating the average number of colony-forming units per milliliter through the plates with colonies. The seed medium and fermentation medium followed the composition in our previous study (Liu et al, 2017). The mediums were adjusted to the particular pH values with 18% hydrochloric acid or 10 mol/L of sodium hydroxide.…”

Two-stage fermentation for lactic acid production on distillery stillage

“…Usually, renewable and low-cost agro-industrial raw materials contain protein macromolecules which need to be further degraded into small peptide molecules and even amino acid before being utilized by LAB (Liu et al, 2017). Although, acid-based hydrolysis of different nitrogen sources has been frequently investigated in order to improve the utilization efficiency, data about application of proteolytic microbes for substrate treatment are still very limited.…”

Biorefining of protein waste for production of sustainable fuels and chemicals

“…A consolidated platform for production of chemical is appealing without the need of processing proteins into amino acids. An illustrative example employs Lactococcus lactis (naturally secreting proteases) for nisin production based on defatted soybean meal [ 129 ]. Amino acids from intracellular hydrolysis of small peptides were utilized to synthesize nisin.…”