Competition-Exclusion for Manganese Is Involved in Antifungal Activity of Two Lactic Acid Bacteria Against Various Dairy Spoilage Fungi

Biopreservation using lactic acid bacteria has gained a growing interest as an alternative to chemical preservatives and/or as a complementary tool to prevent fungal spoilage in dairy products. Among the action mechanisms of antifungal LAB, competitionexclusion for trace elements has recently been highlighted. To further investigate this mechanism, two antifungal LAB strains, <i>Lactiplantibacillus plantarum</i> L244 and <i>Lactobacillus rhamnosus</i> CIRM-BIA1759, were studied in a yogurt model. Firstly, the antifungal activity of these strains against four main dairy spoilage fungi (<i>Penicillium biforme</i>, <i>Mucor racemosus</i>, <i>Galactomyces geotrichum</i> and <i>Yarrowia lipolytica</i>) was evaluated with or without trace element (6 metals and 12 vitamins) supplementation. Only manganese supplementation led to a suppression of the antifungal activity of both <i>L. plantarum</i> L244 and <i>L. rhamnosus</i> CIRM-BIA1759 against <i>P. biforme</i> and/or <i>Y. lipolytica</i>. The scavenging of trace elements was then measured using HR-ICP-MS in both cell-free yogurt whey and fungal biomass. HR-ICP-MS results showed a significant scavenging of Mn in <i>L. plantarum</i> L244 and <i>L. rhamnosus</i> CIRM-BIA1759 whey, as well as Cu for <i>L. rhamnosus</i> CIRM-BIA1759. Moreover, element uptake profiles, including metal and non-metal elements, for each of the target fungi were affected by the use of antifungal cultures. Finally, the role of competitionexclusion for manganese in the inhibition of 25 fungal spoilers was evaluated via oCelloScope growth follow-up. Growth inhibition by antifungal LAB strains was suppressed after Mn supplementation in cell-free whey for the 16 (out of 25) fungi initially inhibited without Mn supplementation. The nine other fungi were not inhibited or were poorly inhibited in the different tested conditions. This study confirmed the role of competitionexclusion for Mn in the antifungal activity of <i>L. plantarum</i> L244 and <i>L. rhamnosus</i> CIRM-BIA1759 strains but also revealed that this mechanism is not generic among fungal species, as the growth behavior of several tested species was not impacted by Mn scavenging.