Caffeic acid from Desikacharya sp. TPB-4: A sustainable source with antimicrobial potential against Aeromonas caviae

The escalating global threat of antimicrobial resistance necessitates the exploration of sustainable natural sources such as cyanobacteria for antioxidant and antimicrobial compounds. In this study, three hot-spring dwelling cyanobacterial strains- Mastigocladus ambikapurensis TA-9, Desikacharya sp. TPB-4 and Westiellopsis sp. TPR-29 were investigated for their bioactive potential. Among these, TPB-4 exhibited the highest total phenolic and flavonoid contents along with strong free-radical scavenging activity. The methanolic extract of TPB-4 demonstrated antimicrobial effects. TLC-purification followed by HR-LCMS analysis revealed caffeic acid as one of the major active constituents. The mechanistic investigations with caffeic acid showed multiple antimicrobial targets including disruption of bacterial (Aeromonas) outer membranes, cell wall integrity and central dogma as evidenced by FTIR and proteomic analyses. These findings highlight the potentiality of hot-spring isolates as natural repositories of bioactive polyphenols, role of proteomics in elucidating antimicrobial targets and suggested caffeic acid as a promising candidate for developing natural antimicrobial therapeutics.