Screening of 44 Baltic Sea Cyanobacterial Strains for Antibacterial and Quorum Sensing Inhibitory Potential:...

Background/Objectives: Cyanobacteria represent a diverse group of microorganisms capable of synthesizing a broad array of biologically active metabolites. Some of these compounds, believed to contribute to the ecological and evolutionary success of cyanobacteria, are increasingly being investigated for potential biomedical and biotechnological applications. They also hold promise in combating the growing threat of antimicrobial resistance (AMR). This screening study aimed to identify Baltic cyanobacterial strains with the potential to produce antibacterial compounds active against streptococci and mycobacteria, as well as quorum sensing inhibitors. Methods/Results: Extracts from forty-four cyanobacterial strains were tested using a broth microdilution assay. The most pronounced activity was observed for extracts derived from two Pseudanabaenaceae strains (KUCC C3 and C4), two Anabaena spp. strains (CCNP 1405 and CCNP 1406), and Aphanizomenon sp. KUCC C1. Inhibition of quorum sensing was the most frequently detected activity, with 30% of the tested extracts inhibiting violacein production in Chromobacterium violaceum ATCC 12472. Growth inhibition of Gram-positive bacteria was less common: 16% of cyanobacterial strains inhibited Streptococcus pyogenes ATCC 12344, and 11% inhibited Mycobacterium smegmatis ATCC 14468. Bioassay-guided fractionation of Aphanizomenon sp. KUCC C1, followed by LC-MS/MS analysis, revealed the presence of glycerolipids and glycolipids, including diacylglycerols (DAGs) and galactosyldiacylglycerols (MGDGs and DGDGs), as major constituents of fractions exhibiting quorum quenching activity. Conclusions: These findings highlight the potential of Baltic cyanobacteria as a source of natural compounds capable of disrupting bacterial communication and growth, offering prospects for the development of novel antimicrobial and anti-virulence agents.