<i>Phyllosticta capitalensis</i>: a novel source of Guignardone A, a high-affinity ligand for penicillin-binding proteins

Endophytic fungi from <i>Pleurolobus gangeticus</i> were isolated, clone purified, identified and subjected to liquid state fermentation. Ethyl acetate extracts of the fermentation product was prepared for antibacterial testing against gram-negative and gram-positive bacteria. Out of the four endophytes isolated, <i>Phyllosticta capitalensis</i> (DLa) showed strong antibacterial activity in the disc diffusion assay with maximum zone of inhibition (27.3 ± 0.6 mm). DLa also had a very low value for Minimum Inhibitory Concentration (10 µg/mL) against all the tested bacteria, indicating its strong broad-spectrum activity. The phytochemical characterisation of DLa showed a meroterpenoid named Guignardone A and three Cyclic dipeptides. <i>In silico</i> studies indicated strong binding affinity between Guignardone A and various penicillin-binding proteins (PBP1, PBP2, PBP2a, PBP3, PBP4 and PBP5) of the above tested bacteria. Further studies are ongoing for optimising the fermentation conditions of <i>P. capitalensis</i> for the enhanced production of Guignardone A.