Lactic acid bacteria-yeast interactions

Abstract

In complex microbial ecosystems constituted by a mixture of different species and strains, interactions will occur between individual microorganisms determining the final ecology. The general environment from which raw food products originate and the microbiological quality of the products in its processed state admits yeast growth. Only part of the primary microflora survives under the selective pressures exerted by the intrinsic and extrinsic biotic factors present in the ecosystem. Eventually, a particular yeast community will develop, and if the environmental factors permit, a specific association would contribute positively or negatively to the final product. Considering wine production, the habitat presents an ecosystem where yeast-yeast, yeastfilamentous fungi and yeast-bacteria interactions can be produced. The symbiosis of them depend on the yeast strain used providing amino acids, peptides and vitamins available as growth factors for lactic acid bacteria (LAB) development, or by the yeast ability to produce metabolic compounds which can act as inhibitors. The flocculation is a phenomenon wherein the cells adhere in clumps and sediments rapidly from the medium in which they are suspended. This property could modify the metabolic behavior of the interacting cells. It is know that many microbes use extracellular signals to transmit information about population density and environmental conditions. As microbes continually need to respond to varying medium conditions, it is not surprising that quorum-sensing regulation that is modulated by physical factors and nutrients availability affect the interactions produced between microorganisms. Recently the reproducible and simple techniques were formulated to study yeast-LAB interaction in simultaneous (both microorganisms in the same medium) and in sequential (growth of LAB in the supernatant modified by yeast growth) growth.