The role of Fe in the browning of medieval model glasses in the presence of the Pseudomonas putida bacteria strain

The Mn-bearing medieval stained-glass windows are affected by a browning phenomenon that could have a microbiological origin. This study investigates the direct and indirect impact of a model Mn-oxidizing and siderophore productive bacterial strain (Pseudomonas putida) on the alteration of medieval glass. For that, five model glasses with variable contents of Mn and Fe were altered during 1 week at 25degree celsius and pH 6.5 either in the presence of the siderophore desferrioxamine B (DFOB) at 50 mM or with the bacterial strain P. putida with or without external sources of iron. DFOB was shown to accelerate the dissolution of the Mn- and Fe -bearing glasses. By contrast, the presence of bacteria, had no apparent effect on glass dissolution, but led to the formation of a biofilm that was enriched in some elements of the glass, especially Si. The results also underlined the key -role of P of the glass as a nutrient for bacterial growth. Brown Mn oxides phases were only formed either when bacteria were incubated with Mn- and P -bearing glasses and after the production of the siderophore pyoverdine. Conversely, no browning was observed for the glass containing MnO and FeO with bacteria, which highlights that the absence of Fe plays a triggering role in the formation of manganese oxides.