Secondary metabolic profiling of Serratia marcescens NP10 reveals new stephensiolides and glucosamine derivatives with bacterial membrane activity

Secondary metabolic profiling, using UPLC-MS E and molecular networking, revealed the secondary metabolites produced by Serratia marcescens NP10. The NP10 strain co-produced cyclic and open-ring stephensiolides (i.e., fatty acyl chain linked to Thr–Ser–Ser–Ile/Leu–Ile/Leu/Val) and glucosamine derivatives (i.e., fatty acyl chain linked to Val–glucose–butyric/oxo-hexanoic acid), with the structures of sixteen new stephensiolides (L–Y) and three new glucosamine derivatives (L–N) proposed. Genome mining identified sphA (stephensiolides) and gcd (glucosamine derivatives) gene clusters within Serratia genomes available on NBCI using antiSMASH, revealing specificity scores of the adenylation-domains within each module that corroborates MS E data. Of the nine RP-HPLC fractions, two stephensiolides and two glucosamine derivatives exhibited activity against Staphylococcus aureus (IC 50 of 25–79 µg/mL). 1 H NMR analysis confirmed the structure of the four active compounds as stephensiolide K, a novel analogue stephensiolide U, and glucosamine derivatives A and C. Stephensiolides K and U were found to cause membrane depolarisation and affect the membrane permeability of S. aureus , while glucosamine derivatives A and C primarily caused membrane depolarisation. New members of the stephensiolide and glucosamine derivative families were thus identified, and results obtained shed light on their antibacterial properties and mode of membrane activity.