The interaction between propionibacteria and lactobacilli in Swiss cheese changes from ______\to ______\when lactic acid is accumulated and lactobacilli starts to benefit from its removal by propionibacteria.
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Initially, only propionibacteria benefit from lactic acid (Commensalism). When lactic acid accumulation threatens lactobacilli, the removal of this acid benefits them too, making the relationship mutually beneficial (Mutualism).