Vermeulen Nicoline, Pavlovic Melanie, Ehrmann Matthias A, Gänzle Michael G, Vogel Rudi F
Food Microbiology and Probiotics, Department of Agricultural, Food and Nutritional Science, 4-10 Ag/For Centre, University of Alberta, Edmonton, AB T6G 2P5, Canada.
Appl Environ Microbiol. 2005 Oct;71(10):6260-6. doi: 10.1128/AEM.71.10.6260-6266.2005.
Protein hydrolysis and amino acid metabolism contribute to the beneficial effects of sourdough fermentation on bread quality. In this work, genes of Lactobacillus sanfranciscensis strain DSM 20451 involved in peptide uptake and hydrolysis were identified and their expression during growth in sourdough was determined. Screening of the L. sanfranciscensis genome with degenerate primers targeting prt and analysis of proteolytic activity in vitro provided no indication for proteolytic activity. Proteolysis in aseptic doughs and sourdoughs fermented with L. sanfranciscensis was inhibited upon the addition of an aspartic protease inhibitor. These results indicate that proteolysis was not linked to the presence of L. sanfranciscensis DSM 20451 and that this strain does not harbor a proteinase. Genes encoding the peptide transport systems Opp and DtpT and the intracellular peptidases PepT, PepR, PepC, PepN, and PepX were identified. Both peptide uptake systems and the genes pepN, pepX, pepC, and pepT were expressed by L. sanfranciscensis growing exponentially in sourdough, whereas pepX was not transcribed. The regulation of the expression of Opp, DtpT, and PepT during growth of L. sanfranciscensis in sourdough was investigated. Expression of Opp and DtpT was reduced approximately 17-fold when the peptide supply in dough was increased. The expression of PepT was dependent on the peptide supply to a lesser extent. Thus, the accumulation of amino nitrogen by L. sanfranciscensis in dough is attributable to peptide hydrolysis rather than proteolysis and amino acid metabolism by L. sanfranciscensis during growth in sourdough is limited by the peptide availability.
蛋白质水解和氨基酸代谢有助于酸面团发酵对面包品质产生有益影响。在本研究中，鉴定了旧金山乳杆菌DSM 20451菌株中参与肽摄取和水解的基因，并测定了其在酸面团生长过程中的表达。用靶向prt的简并引物筛选旧金山乳杆菌基因组并分析体外蛋白水解活性，未发现蛋白水解活性的迹象。在无菌面团和用旧金山乳杆菌发酵的酸面团中添加天冬氨酸蛋白酶抑制剂后，蛋白水解受到抑制。这些结果表明，蛋白水解与旧金山乳杆菌DSM 20451的存在无关，且该菌株不含有蛋白酶。鉴定了编码肽转运系统Opp和DtpT以及细胞内肽酶PepT、PepR、PepC、PepN和PepX的基因。肽摄取系统以及pepN、pepX、pepC和pepT基因在酸面团中指数生长的旧金山乳杆菌中均有表达，而pepX未转录。研究了旧金山乳杆菌在酸面团生长过程中Opp、DtpT和PepT表达的调控。当面团中的肽供应增加时，Opp和DtpT的表达降低了约17倍。PepT的表达在较小程度上依赖于肽供应。因此，旧金山乳杆菌在面团中积累氨基氮归因于肽水解，并且旧金山乳杆菌在酸面团生长过程中的氨基酸代谢受肽可用性的限制。
