Isolation, screening, and optimization of bacterial strains for novel transglutaminase production

Update of the list of qualified presumption of safety (QPS) recommended microbiological agents intentionally added to food or feed as notified to EFSA 21: Suitability of taxonomic units notified to EFSA until September 2024

The qualified presumption of safety (QPS) process was developed to provide a safety assessment approach for microorganisms intended for use in food or feed chains. In the period covered by this Statement, no new information was found that would change the status of previously recommended QPS taxonomic units (TUs). The TUs in the QPS list were updated based on a verification, against their respective authoritative databases, of the correctness of the names and completeness of synonyms. Of 54 microorganisms notified to EFSA between April and September 2024 (33 as feed additives, 17 as food enzymes or additives, 4 as novel foods), 50 were not evaluated because: 12 were filamentous fungi, 1 was Enterococcus faecium and 8 were Escherichia coli (all excluded from the QPS evaluation), and 29 were TUs that already have a QPS status. One notification (Ensifer adhaerens) was already evaluated in a previous Panel Statement. Another notification (Enterococcus lactis) was already evaluated in the previous 3-year QPS cycle and was reassessed within this document. Two TUs were notified for the first time and were assessed for a possible QPS status: Serratia plymuthica and Lacticaseibacillus huelsenbergensis. Bacillus thuringiensis and Bacillus nakamurai have been assessed for a possible QPS status in response to internal requests. The following was concluded on the five assessed TUs. L. huelsenbergensis can be granted the QPS status based on its close relatedness to several other QPS Lacticaseibacillus species. E. lactis is not recommended for the QPS status due to insufficient information on safety. S. plymuthica and B. thuringiensis are not recommended for the QPS status due to safety concerns. B. nakamurai cannot be recommended for the QPS list due to a lack of body of knowledge for its use in the food and feed chain.

Secretion of Bacillus amyloliquefaciens Transglutaminase from Lactococcus lactis and Its Enhancement of Food Gel Properties

(1) Background: Microbial transglutaminases (MTGase) catalyze protein crosslink. This is useful in the food industry to improve gelation, water holding capacity, and emulsifying capacity during foodstuff manufacturing. The production of MTGase in wild-type strains renders low yield and high costs of downstream purification, limiting its industrial applications. (2) Methods: In this work, MTGase from Bacillus amyloliquefaciens BH072 (BaMTGase) has been heterologously expressed in Lactococcus lactis, using the signal peptide Usp45 to direct the secretion of recombinant BaMTGase out of the cell for easier purification. (3) Results: In these conditions, MTGase was purified with a high yield (48.7 ± 0.2 mg/L) and high enzyme activity (28.6 ± 0.5 U/mg). Next, BaMTGase was tested for industrial applications. Recombinant BaMTGase and commercial MTGase were used for SPI solution crosslinking. BaMTGase formed a harder gel with higher water-holding capacity and a dense and smooth gel microstructure. (4) Conclusions: This work provides an attractive food-grade cell factory for the food industry and offers a suitable chassis for MTGase production.

Effect of key regulators in augmenting transcriptional expression of Transglutaminase in Streptomyces mobaraensis

Transglutaminase forms isopeptide bonds in proteins which are helpful in various industrial applications. However, low productivity and high cost are the major bottlenecks for industrial Transglutaminase production. The present study describes the regulatory mechanism of microbial Transglutaminase (MTGase) biosynthesis from Streptomyces mobaraensis and the effect of key regulators to maximize production. The transcriptional responses under the effect of various key modulators of MTGasebiosynthesis were evaluated. Productivity of MTGase with novel biosynthesis approach by regulators augmentation was correlated by transcriptional profiling. The optimization by key modulators by combinational supplementation led to 2-fold rise in activity. The functional attributes, the copy number of MTGase gene and relative changes were assessed by Real-Time quantitative PCR. Protease, MgCl₂, CTAB induced upregulation, whereas PMSF, NaF and bleomycin sulphate showed inhibitory action on MTGase production and activity. The optimization by combinational supplementation of key modulators led to 4.27-fold increase (6.11 IU/mL) in production.

Expression of Bacillus amyloliquefaciens transglutaminase in recombinant E. coli under the control of a bicistronic plasmid system in DO-stat fed-batch bioreactor cultivations

We studied the expression of Bacillus amyloliquefaciens transglutaminase cloned in Escherichia coli BL21(DE3)pLysS harboring the plasmid pBAD/3C/bTGase, a bicistronic expression system, in bioreactor cultivation. Batch and fed-batch controlled as DO-stat strategies were employed for the production of the recombinant enzyme. In 30 h-batch cultivations using Terrific broth (TB), 6 g/L of biomass and 3.12 U/mg_protein of transglutaminase activity were obtained. DO-stat fed-batch cultivations under the control of oxygen concentration (DO-stat) using TB as medium but fed with glucose allowed the increment in biomass formation (17.5 g/L) and enzyme activity (6.43 U/mg_protein). DO-stat fed-batch using mineral medium (M9) and fed with glucose under the same conditions produced even higher enzymatic activity (9.14 U/mg_protein). The pH effect was investigated, and the best enzymatic activity could be observed at pH 8. In all cultivations, the bicistronic system remained stable, with 100% of plasmid-bearing cells. These results show that E. coli bearing bicistronic plasmid constructs to express recombinant TGase could be cultivated in bioreactors under DO-stat fed-batch using mineral medium and it is a promising strategy in future optimizations to produce this important enzyme.

Heterologous Expression of Recombinant Transglutaminase in Bacillus subtilis SCK6 with Optimized Signal Peptide and Codon, and Its Impact on Gelatin Properties

Microbial transglutaminases (MTGs) are widely used in the food industry. In this study, the MTG gene of Streptomyces sp. TYQ1024 was cloned and expressed in a food-grade bacterial strain, Bacillus subtilis SCK6. Extracellular activity of the MTG after codon and signal peptide (SP Ync M) optimization was 20 times that of the pre-optimized enzyme. After purification, the molecular weight of the MTG was 38 kDa and the specific activity was 63.75 U/mg. The optimal temperature and pH for the recombinant MTG activity were 50°C and 8.0, respectively. MTG activity increased 1.42- fold in the presence of β-ME and 1.6-fold in the presence of DTT. Moreover, 18% sodium chloride still resulted in 83% enzyme activity, which showed good salt tolerance. Cross-linking gelatin with the MTG increased the strength of gelatin 1.67 times and increased the thermal denaturation temperature from 61.8 to 75.8°C. The MTG also significantly increased the strength and thermal stability of gelatin. These characteristics demonstrated the huge commercial potential of MTG, such as for applications in salted protein foods.