Interactions of PKS gene expression and antimicrobial and antibiofilm activity levels in the lichen-forming fungus Hypogymnia tubulosa due to light and heat stress

Lichens synthesize a variety of secondary metabolites that enable them to tolerate abiotic stress factors. Many of these metabolites possess significant potential for pharmaceutical and industrial applications, making their enhanced production a desirable goal. This study aimed to investigate the effects of light and heat stress on the expression levels of polyketide synthase (PKS) genes, which are involved in metabolite production, as well as the impact on antimicrobial and antibiofilm activity in the lichen-forming fungus (LFF) cultured from Hypogymnia tubulosa. To achieve this, the LFF H. tubulosa, collected from Turkey, was cultured and grown for 15 and 30 days before being subjected to light and heat stress conditions. The expression levels of PKS genes in the stress-exposed samples were quantified using quantitative polymerase chain reaction (qPCR). Subsequently, the antibacterial and antibiofilm activities of the extracts from these stressed samples against Pseudomonas aeruginosa PAO1 and Staphylococcus aureus were assessed using a microplate reader. The results indicated a significant up-regulation of PKS gene expression in 15-day-old samples under light stress. Additionally, extracts from the natural thalli exhibited the highest inhibition rate (94.14%) against S. aureus at a concentration of 120 mu g/mL, while extracts from 30-day-old samples exposed to 15 degrees C-light demonstrated the highest inhibition rate (53.54%) against P. aeruginosa at a concentration of 480 mu g/mL. Notably, low doses of 15-day-old samples exposed to stress conditions displayed strong antibiofilm activity against both bacterial species. Extracts derived from cultured samples frequently showed greater effectiveness. These findings suggest that altering culture conditions may facilitate the discovery of new, effective metabolites.