The exposure of lactic acid bacteria (LAB) to stressful conditions during fermentation involves a broad transcriptional response with many induced or repressed genes. The complex network of such responses will reflect upon the composition and organoleptic properties of the dough and final products. The over-production of 2-methylbutyric (2MetBut) and 3-methylbutyric (3MetBut) acids, by LAB, has been detected following exposure to different sublethal stress conditions. Serrazanetti et al. (2011) reported the over-production of these two compounds in Lactobacillus sanfranciscensis during acidic stress when the cells were grown in the presence of leucine (Leu) as the only branched chain amino acids (BCAAs) source. Metabolites coming from BCAAs catabolism increased up to seven times under acid stress (pH 3.6 and 5.8). Moreover, the gene expression analysis confirmed that some genes associated with BCAAs catabolism were overexpressed under acid conditions. The experiment with labelled Leu showed that 2MetBut originated also from Leu. While the overproduction of 3MetBut under acid stress can be attributed to the need to maintain a redox balance, the rationale for the production of 2MetBut from Leu can be found in a newly proposed biosynthesis pathway leading to 2MetBut and 3 mol of ATP per mol of Leu. But why do LAB need to catabolize in excess BCAAs in the presence of sublethal stress if they do not generate energy? A possible answer, suggested by Goffin et al. (2010), lies in the end products of BCAAs catabolism, a number of which could serve as signalling molecules for the interaction of Lactobacillus plantarum with its environment and maybe itself. In order to support this hypothesis the possible signalling-effect of 2MetBut and 3MetBut on the growth and the metabolism of some strains of LAB has been investigated. In particular, L. plantarum, L. sanfranciscensis and Lactobacillus brevis were exposed to BCAAs catabolism end products for 2 and 24 hours after which the volatile metabolites and the expression of some genes involved in Leu catabolism were analysed by GC-MS-SPME and RT-PCR, respectively.
2-methyibutyric and 3-methylbutyric acids: possible components of a feed back loop under stress conditions? / Serrazanetti, D; Gottardi, D; Montanari, C; Vannini, L. - STAMPA. - (2011), pp. 37-40. (Intervento presentato al convegno FIRST INTERNATIONAL CONFERENCE ON MICROBIAL DIVERSITY 2011 - ENVIRONMENTAL STRESS AND ADAPTATION, MD 2011 tenutosi a MILAN, ITALY nel 26- 28 OCTOBER 2011).
2-methyibutyric and 3-methylbutyric acids: possible components of a feed back loop under stress conditions?
SERRAZANETTI, DIANA ISABELLA;GOTTARDI, DAVIDE;MONTANARI, CHIARA;VANNINI, LUCIA
2011
Abstract
The exposure of lactic acid bacteria (LAB) to stressful conditions during fermentation involves a broad transcriptional response with many induced or repressed genes. The complex network of such responses will reflect upon the composition and organoleptic properties of the dough and final products. The over-production of 2-methylbutyric (2MetBut) and 3-methylbutyric (3MetBut) acids, by LAB, has been detected following exposure to different sublethal stress conditions. Serrazanetti et al. (2011) reported the over-production of these two compounds in Lactobacillus sanfranciscensis during acidic stress when the cells were grown in the presence of leucine (Leu) as the only branched chain amino acids (BCAAs) source. Metabolites coming from BCAAs catabolism increased up to seven times under acid stress (pH 3.6 and 5.8). Moreover, the gene expression analysis confirmed that some genes associated with BCAAs catabolism were overexpressed under acid conditions. The experiment with labelled Leu showed that 2MetBut originated also from Leu. While the overproduction of 3MetBut under acid stress can be attributed to the need to maintain a redox balance, the rationale for the production of 2MetBut from Leu can be found in a newly proposed biosynthesis pathway leading to 2MetBut and 3 mol of ATP per mol of Leu. But why do LAB need to catabolize in excess BCAAs in the presence of sublethal stress if they do not generate energy? A possible answer, suggested by Goffin et al. (2010), lies in the end products of BCAAs catabolism, a number of which could serve as signalling molecules for the interaction of Lactobacillus plantarum with its environment and maybe itself. In order to support this hypothesis the possible signalling-effect of 2MetBut and 3MetBut on the growth and the metabolism of some strains of LAB has been investigated. In particular, L. plantarum, L. sanfranciscensis and Lactobacillus brevis were exposed to BCAAs catabolism end products for 2 and 24 hours after which the volatile metabolites and the expression of some genes involved in Leu catabolism were analysed by GC-MS-SPME and RT-PCR, respectively.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
