Effect of the addition of cysteine and phenylalanine on growth of lactic acid nacteria from oranges

M. B. PÉREZ AND F. M. SAGUIR

Tucumán

Congreso; VII Congreso Argentino de Microbiología General “SAMIGE del Bicentenario; 2011

Lactic acid bacteria (LAB) are fastidious microorganisms towards nutritional. Furthermore, they have (in most cases) limited biosynthetic ability, requiring an exogenous source of aminoacids or peptides for optimum growth. In a previous study we isolated and identified LAB from orange juice. Based on their capacity to produce hydrogen sulfide from cysteine added to orange juice strains of <i>Lactobacillus plantarum</i> and <i>Leuconostoc mesenteroides</i> subsp. <i>mesenteroides</i  were saelected. The aim of this study was  to evaluate the effect of cysteine and/or methionine on  the growth of  <i>Lact. plantarum</i> JNB21 y JNB25 and Leuconostoc mesenteroides subsp mesenteroides</i> JNB9 of <i> in a modified MRS medium,  pH 6,5 (MRSM),from which the main sources of nitrogen were omitted. At the same time the hydrogen sulphured production was evaluated from cysteine catabolism. Cysteine and/or penylalanine were added to MRSM at 0,2 and 1g/l. Bacterial cultures were inoculated at a rate of 2%, and incubated at 30°C for 24 h. Growth was determined by counting cfu/ml at 30ºC.  Qualitative hydrogen Sulphured was analyzed under experimental conditions.    In MRSM <i>Lact. plantarum</i> JNB21 y JNB25 multiplied in a significantly more extent than  <i>Leuc. mesenteroides</i> strain, with a growth rate of 0,41 and 1,1 h^-1 and final biomass of 8,33 and 10,04 log cfu/ml, respectively. Addition of 0.2 g/l of Cys or Phe stimulated Lact. plantarum JN21 growth. By contrast, Cys and Phe in concentration of 1 g/l decreased its growth rate of about 19.5 %. For Lact. plantarum JNB25 strain the amino acids to deficient MRSM medium retarded growth under all assayed conditions, reaching in presence of 1 g/l of Cys, the lowest final biomass (9.68 log cfu/ml) and growth rate (0.5 h^-1). Independently of growth conditions a terminal pH drop occurred. When Cyst was included in the MRSM mediun hydrogen sulphide was produced in all cultures, indicating that Cyst was degraded. Considering the growth responses under deficient nutritional condition, we infer that Leuc, mesenteroides</i> subsp. <i>mesenteroides</i> strain could have higher nutritional requirements than Lact. plantarum strains. However, the addition of test amino acids did not modify its behaviour  suggesting that Cys and Phe would not be essentials for growth or that their concentrations in the natural medium would be enough for development. At low concentration Cys or Phe increased Lact. plantarum  growth parameters, but at the highest one they inhibited growth possibly related to a controlling effect of biosynthetic pathways. These results suggest that the Lact. plantarum strains could show the highest possibility to growth in the natural medium orange juice without producing hydrogen sulpide.