Analysis of the presence of prtR proteinase gene in natural isolates of Lactobacillus rhamnosus

Characterization of Cell-Envelope Proteinases from Two Lacticaseibacillus casei Strains Isolated from Parmigiano Reggiano Cheese

In the present work, two cell-envelope proteinases (CEPs) from Lacticaseibacillus casei strains PRA205 and 2006 were characterized at both the biochemical and genetic levels. The genomes of both L. casei strains included two putative CEPs genes prtP2 and prtR1, but only prtR1 was transcribed. The extracted PrtR1 proteinases were serine proteinases with optimal activity at 40 °C and pH 7.5, and were activated by Ca²⁺ ions. Interestingly, PrtR1 from L. casei PRA205 exhibited high residual activity at pH 4 and at 5 °C, suggesting its possible exploitation for fermented food production. The caseinolytic activity against αS1- and β-casein indicated that both PrtR1s belonged to the PI/PIII type. These PrtR1s cleaved β-casein peptide bonds preferentially when amino acid M or N was present at the P1 subsite and amino acids A and D were at the P1' subsite. Several bioactive peptides were found to be released from PrtR1 after αs1- and β-casein hydrolysis.

Characteristics of the Proteolytic Enzymes Produced by Lactic Acid Bacteria

Over the past several decades, we have observed a very rapid development in the biotechnological use of lactic acid bacteria (LAB) in various branches of the food industry. All such areas of activity of these bacteria are very important and promise enormous economic and industrial successes. LAB are a numerous group of microorganisms that have the ability to ferment sugars into lactic acid and to produce proteolytic enzymes. LAB proteolytic enzymes play an important role in supplying cells with the nitrogen compounds necessary for their growth. Their nutritional requirements in this regard are very high. Lactic acid bacteria require many free amino acids to grow. The available amount of such compounds in the natural environment is usually small, hence the main function of these enzymes is the hydrolysis of proteins to components absorbed by bacterial cells. Enzymes are synthesized inside bacterial cells and are mostly secreted outside the cell. This type of proteinase remains linked to the cell wall structure by covalent bonds. Thanks to advances in enzymology, it is possible to obtain and design new enzymes and their preparations that can be widely used in various biotechnological processes. This article characterizes the proteolytic activity, describes LAB nitrogen metabolism and details the characteristics of the peptide transport system. Potential applications of proteolytic enzymes in many industries are also presented, including the food industry.

Cell-envelope proteinases from lactic acid bacteria: Biochemical features and biotechnological applications

Proteins displayed on the cell surface of lactic acid bacteria (LAB) perform diverse and important biochemical roles. Among these, the cell-envelope proteinases (CEPs) are one of the most widely studied and most exploited for biotechnological applications. CEPs are important players in the proteolytic system of LAB, because they are required by LAB to degrade proteins in the growth media into peptides and/or amino acids required for the nitrogen nutrition of LAB. The most important area of application of CEPs is therefore in protein hydrolysis, especially in dairy products. Also, the physical location of CEPs (i.e., being cell-envelope anchored) allows for relatively easy downstream processing (e.g., extraction) of CEPs. This review describes the biochemical features and organization of CEPs and how this fits them for the purpose of protein hydrolysis. It begins with a focus on the genetic organization and expression of CEPs. The catalytic behavior and cleavage specificities of CEPs from various LAB are also discussed. Following this, the extraction and purification of most CEPs reported to date is described. The industrial applications of CEPs in food technology, health promotion, as well as in the growing area of water purification are discussed. Techniques for improving the production and catalytic efficiency of CEPs are also given an important place in this review.

Diversity of non-starter lactic acid bacteria in autochthonous dairy products from Western Balkan Countries - Technological and probiotic properties

The aim of this review was to summarize the data regarding diversity of non-starter lactic acid bacteria (NSLAB) isolated from various artisanal dairy products manufactured in Western Balkan Countries. The dairy products examined were manufactured from raw cow's, sheep's or goat's milk or mixed milk, in the traditional way without the addition of commercial starter cultures. Dairy products such as white brined cheese, fresh cheese, hard cheese, yogurt, sour cream and kajmak were sampled in the households of Serbia, Croatia, Slovenia, Bosnia and Herzegovina, Montenegro, and North Macedonia. It has been established that the diversity of lactic acid bacteria (LAB) from raw milk artisanal dairy products is extensive. In the reviewed literature, 28 LAB species and a large number of strains belonging to the Lactobacillus, Lactococcus, Enterococcus, Streptococcus, Pediococcus, Leuconostoc and Weissella genera were isolated from various dairy products. Over 3000 LAB strains were obtained and characterized for their technological and probiotic properties including: acidification and coagulation of milk, production of aromatic compounds, proteolytic activity, bacteriocins production and competitive exclusion of pathogens, production of exopolysaccharides, aggregation ability and immunomodulatory effect. Results show that many of the isolated NSLAB strains had one, two or more of the properties mentioned. The data presented emphasize the importance of artisanal products as a valuable source of NSLAB with unique technological and probiotic features important both as a base for scientific research as well as for designing novel starter cultures for functional dairy food.

Evaluation of antibacterial activity of Stenotrophomonas maltophilia against Ralstonia solanacearum under different application conditions

AIM

The aim of this study was the monitoring of different mechanisms involved in the antibacterial activity of the biocontrol agent, Stenotrophomonas maltophilia (PD4560), against Ralstonia solanacearum in vitro and in vivo. Optimization of conditions that favour these mechanisms was the second target of this study.

METHODS AND RESULTS

Proteolytic activity of Sten. maltophilia (PD 4560), was tested on skimmed milk medium. The biocontrol agent was able to produce an alkaline serine protease enzyme with a molecular weight of 40 KDa as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses. Spraying of salicylic acid (SA) led to an increase in the efficacy of Sten. maltophilia in controlling the Ralstonia potato wilt while spraying of ammonium sulphate (AmS) did not affect the biocontrol efficacy. The efficacy was correlated with the expression of protease enzyme genes; Prt genes (mainly PrtP and Prt4) and PR genes (mainly PR-1 and PRQ) as evaluated using real-time polymerase chain reaction analysis.

CONCLUSIONS

The biocontrol activity of Sten. maltophilia can be attributed to the direct mechanism alkaline serine proteolytic enzyme production and through induction of host systemic acquired resistance as indirect mechanism. Tuber bulking was the most suitable physiological growth stage to apply either SA or the biocontrol agent.

SIGNIFICANCE AND IMPACT OF THE STUDY

Both SA and peat-moss as an organic carrier enhanced the antibacterial efficiency of the biocontrol agent. Application of Sten. maltophilia is more suitable under alkaline soil conditions.

Characterization of the mature cell surface proteinase of Lactobacillus delbrueckii subsp. lactis CRL 581

The cell envelope-associated proteinase (CEP) of Lactobacillus delbrueckii subsp. lactis CRL 581 (PrtL) has an essential role in bacterial growth, contributes to the flavor and texture development of fermented products, and can release bioactive health-beneficial peptides during milk fermentation. The genome of L. delbrueckii subsp. lactis CRL 581 possesses only one gene that encodes PrtL, which consists of 1924 amino acids and is a multidomain protein anchored to the cell via its W domain. PrtL was extracted from the cell under high ionic strength conditions using NaCl, suggesting an electrostatic interaction between the proteinase and the cell envelope. The released PrtL was purified and biochemically characterized; its activity was maximal at temperatures between 37 and 40 °C and at pH between 7 and 8. Under optimal conditions, PrtL exhibited higher affinity for succinyl-alanyl-alanyl-prolyl-phenylalanine-p-nitroanilide than for succinyl-alanyl-glutamyl-prolyl-phenylalanine-p-nitroanilide, while methoxy-succinyl-arginyl-prolyl-tyrosyl-p-nitroanilide was not degraded. A similar α- and β-casein degradation pattern was observed with the purified and the cell envelope-bound proteinase. Finally, on the basis of its specificity towards caseins and the unique combination of amino acids at residues thought to be involved in substrate specificity, PrtL can be classified as a representative of a new group of CEP.