Optimized standard conditions for determination of nitrate reduction in propionibacteria

Abstract

Nitrate reduction is currently considered to be a key characteristic for the determinative grouping of strains of the Propionibacterium but many controversies exist regarding nitrate reduction by members of this genus. The aim was thus to determine the influence of different media, nitrate concentrations and pH values under aerobic and anoxic conditions, using the conventional technique and the diazotization coupling method, on the nitrate reducing capability of propionibacteria. The low concentrations of nitrite formed during nitrate reduction by the propionibacteria could not be accurately determined using the conventional technique. This method was found to be reliable only when the initial KNO3 concentration exceeded 1.0 mmol/L. In contrast, with high concentrations of nitrite, the diazotization coupling method was found to be too sensitive. Nitrate reduction in the yeast extract lactate (YEL) medium with added glucose and KNO3, was not effective as only low concentrations of nitrite were produced. Good nitrate reduction was obtained on both the YEL and yeast extract (YE) media with or without the addition of KNO3 (pH 8.0) to the test media. The presence of nitrite in the YEL culture media of the five Propionibacterium type strains, under aerobic conditions (pH 8.0) with 20 mmol/L KNO3, was determined using the diazotization coupling method. The type strains of P. acidipropionici, P. acnes and P. freudenreichii subsp. freudenreichii were able to reduce nitrate. In contrast, the P. jensenii and P. thoenii type strains were not able to reduce nitrate under these conditions. Furthermore, P. acidipropionici and P. acnes were both able to further reduce the formed nitrite to gaseous nitrogen. It was found that nitrate reduction was strongly influenced by environmental factors such as oxygen, nitrate concentration, pH, media composition, incubation period and the presence of glucose. Data are presented which permit a more standardized determination of nitrate reduction of propionibacteria. © Inra/Elsevier, Paris.