Catabolism of Serine by Pediococcus acidilactici and Pediococcus pentosaceus

Abstract

The ability to produce diacetyl from pyruvate and L-serine was studied in various strains of Pediococcus pentosaceus and Pediococcus acidilactici isolated from cheese. After being incubated on both substrates, only P. pentosaceus produced significant amounts of diacetyl. This property correlated with measurable serine dehydratase activity in cell extracts. A gene encoding the serine dehydratase (dsdA) was identified in P. pentosaceus, and strains that showed no serine dehydratase activity carried mutations that rendered the gene product inactive. A functional dsdA was cloned from P. pentosaceus FAM19132 and expressed in Escherichia coli. The purified recombinant enzyme catalyzed the formation of pyruvate from L-and D-serine and was active at low pH and elevated NaCl concentrations, environmental conditions usually present in cheese. Analysis of the amino acid profiles of culture supernatants from dsdA wild-type and dsdA mutant strains of P. pentosaceus did not show differences in serine levels. In contrast, P. acidilactici degraded serine. Moreover, this species also catabolized threonine and produced alanine and ␣-aminobutyrate. Pediococcus pentosaceus and Pediococcus acidilactici are homofermentative Gram-positive cocci that produce D-and L-lactate from carbohydrates. These bacteria are regularly found in the nonstarter population of raw milk cheeses at the end of the ripening process. Thus, Pediococcus spp. were isolated from cheddar, ewes' milk cheeses, Comté, AOC Salers, Puzzone di Moena, and various raw milk cheeses traditionally produced in Switzerland, such as Gruyère, Emmentaler, Appenzeller, and Tilsit (1-8).Although several reports have indicated that pediococci alone or combined with lactobacilli can accelerate cheese ripening and enhance flavor development, respectively (9-13), knowledge about metabolic activities affecting the maturation of cheese is limited. Studies on the physiological and biochemical activities of Pediococcus spp. have mainly focused on carbohydrate metabolism and proteolytic and lipolytic activities (14-16). Researchers have also reported that pediococci racemize L-lactate to D-lactate under anaerobic conditions and that pediococci can oxidize lactate to acetate and carbon dioxide under aerobic conditions (17). However, information on the enzymatic degradation of amino acids, important precursors for flavor compounds, is sparse.Diacetyl contributes to desirable flavor in fermented dairy products. A pathway well-known for producing diacetyl is through degradation of citrate (18). In this pathway, pyruvate is formed as an intermediary compound that is then converted via ␣-acetolactate to diacetyl. Although pediococci do not appear to utilize citrate, these species have been reported to form diacetyl (19,20). Pyruvate, which is derived from the metabolism of carbohydrates or amino acids, is likely used for synthesizing diacetyl.In this study, the ability of various strains of P. acidilactici and of P. pentosaceus isolated from cheese to produce diacetyl from pyruvate and serine wa...

The individual contribution of starter and non-starter lactic acid bacteria to the volatile organic compound composition of Caciocavallo Palermitano cheese

“…These compounds have a characteristic odor and a low perception thresholds. Among the ketones identified, 2,3-butanedione (diacetyl), detected at high levels for L. casei and L. rhamnosus, and its reduction product 2-butanone, 3-hydroxy-(acetoin), significantly associated to P. pentosaceus, are mainly associated to pyruvate, lactose or citrate metabolism by some LAB starters (Irmler et al, 2013). In fact, acetoin was not detected in CuBM confirming that this compound is only generated during fermentation.…”

Glucose Consumption and Lactic Acid Formation in Millet Sourdough Fermented With Different Strains of Lactic Acid Bacteria

“…Pediococcus pentosaceus and Pediococcus acidilactici are important LABs involved as starter cultures in meat, vegetable and dairy fermentation and causing characteristic flavor changes, improving hygienic quality and extending the shelf life of several products (Irmler et al 2013). Lactobacillus coryniformis has been recently reported to display a variety of potential probiotic properties, to be characterized by a strong antifungal activity and potential to be used as a biopreservative in feed systems (Magnusson, Schnurer, 2001;Sekwati-Monang et al 2012).…”

Natural Flavours Obtained by Microbiological Pathway

“…Pediococcus acidilactici and P. pentosaceus can convert alanine to pyruvate by α-ketoacid intermediary pyruvate which further is converted to flavour compounds [22]. The diacetyl and acetoin are produced via citrate metabolism by citrate-positive LAB (L. lactis, Lb.…”

“…By oxidative deamination of the serine under the Lb. plantarum UC1001 metabolism, acetic acid is detected [5,12], while P. pentosaceus and P. acidilactici are able to produce diacetyl from pyruvate and L-serine [22].…”