Modification of nitrogenous compounds by lactic acid bacteria interactions

Abstract

The microorganisms are members of larger environmental communities. Each one has an effect on its environment and influences all the other residents of the community. The effect of one population on another can be detrimental to either or both, neutralistic or beneficial to both. Physical conditions and chemical composition of the niche are crucial determinants of which species can develop. Protein is an important carbon and nitrogen source for bacterial communities. This compound is only available for growth when proteolytic enzymes are present in the extracellular medium because only small peptides and free amino acids can be transported across the bacterial cell membrane. Mixed or co-culture system have been recognized to be effective for certain fermentations. In yogurt, Lactobacillus bulgaricus that has high proteolytic activity supply free amino acids to Streptococcus thermophilus growth establishing cooperation between both bacteria. In the symbiosis between lactic acid bacteria (LAB) on natural kefir starter, the Lact. helveticus strain produces amino acids that are utilized to create a symbiotic bioconsortium with the other LAB. This interaction enhanced lactic acid production and intensified cell growth activity compared to individual cultures. The accumulation of free amino acids including essential amino acids in the final kefir is greater than that of yogurt. It was determined that in a mixed culture of a proteolytic Oenococcus oeni strain with a non-proteolytic Pediococcus pentosaceus strain from wine, the former develop higher proteolytic activity than in pure culture. Consequently the cell growth and the amount of free essential amino acids increase for both microorganisms.