Condition-dependent expression of CotA laccase in Bacillus licheniformis reveals sporulation-linked activity and associated pigment formation.

Bacterial laccases remain comparatively undercharacterized, particularly regarding the factors that influence their induction. In contrast, fungal laccases have been considerably researched and are known to be expressed under diverse physiological and environmental conditions. Existing literature provides limited insight into the environmental triggers associated with the expression of bacterial laccase genes. Our study evaluated Bacillus licheniformis CotA laccase activity in the presence of known fungal laccase inducers as well as oxidative stress and found no significant effect on induction. Comparative analysis between nutrient-rich and sporulation-promoting conditions revealed a ~ 4-5-fold increase in CotA activity and a ~ 4-fold increase in cotA gene expression during sporulation. Moreover, CotA was linked to the biosynthesis of a melanin-like pigment, as pigment yield correlated with laccase activity and decreased upon inhibitor treatment. Notably, sodium azide reduced pigment formation without inhibiting sporulation, indicating that CotA contributes to the pigmentation process rather than to spore development itself. These results showcase that CotA expression in B. licheniformis is primarily sporulation dependent.