Symbiosis describes specific interactions that cannot be performed alone, and like synergism, are not necessary for survival. One case of mutualism is the action between L. arabinosus and S. faecalis which release phenylalanine and folic acid respectively. There are numerous cases of symbiosis involving plant and animals and microbes, e.g., the interaction of insects with yeast. Association which is detrimental to one species and neutral to the other. In amensalism, the unaffected population releases agents such as antibiotics that restrict the the growth of the other population.
Amensalistic interactions can induce dormancy or morphogenesis in the antagonized population.
One case with relevance to the milk fermentation process is the interaction between the nisin-producing S. lactis and the restricted L. casei. Non-specific amensalism can result from the lowering of the system pH or the production of oxygen or hydrogen peroxide. There is some overlap between amensalism and competition, although the latter must be a two-way process. Association in which one organism is benefitted and the other organism is neither benefitted nor harmed. Commensalism is common and is a significant factor in organism succession within microbial communities.