Evaluation of a quantitative screening method for hydrogen sulfide production by cheese-ripening microorganisms: the first step towards l-cysteine catabolism

A practical adaptation of the methylene blue reaction for hydrogen sulfide quantification was developed to perform microbial selection. Closed plate flasks containing a zinc-agar layer above the liquid microbial culture are proposed as a trap system where the H(2)S can be retained and then quantified by the methylene blue reaction. Using this quantitative method, the ability to produce H(2)S was studied in several cheese-ripening microorganisms. Our aim was to select strains that produce the highest quantities of H(2)S as the main product of L-cysteine catabolism. Thirty seven yeast and bacteria strains were cultivated with or without L-cysteine. The separation between the growth medium and the H(2)S trapping layer displayed good performance: all the studied strains grew efficiently and only negligible loss of H(2)S was observed during culturing. The strains displayed large differences in their H(2)S production capabilities: yeast strains were greater producers of H(2)S than bacteria with production strain-related in both cases. Furthermore, the relationship between H(2)S production and L-cysteine consumption was analyzed, which made it possible for us to select microorganisms with high capacity in L-cysteine degradation. The production of volatile sulfur compounds was also studied and the possible effect of culture pH and metabolic differences between strains are discussed.