Spectrum of action of C16-C17 fengycins, cyclic lipopeptides with promising antibacterial activity produced by Bacillus velezensis MEP218

MEDEOT, DANIELA; BASSO, VANESA; FERNANDEZ, MARILINA; BOSCH, ALEJANDRA; ESTRELLA, MARIA JULIA; SANNAZZARO, ANALIA INÉS; TORRES TEJERIZO, GONZALO; PISTORIO, MARIANO; JOFRÉ, EDGARDO

Congreso; XVIII Congreso de la Sociedad Argentina de Microbiología General; 2023

The WHO warns that antimicrobial resistance (AMR) is one of the greatest threats to global health, food security, and development. The increase in AMR exacerbates the demand for new antimicrobial agents. To contribute to the mitigation of this problem, the challenge is the discovery of new antimicrobials for the control of pathogenic bacteria. Our laboratory studies cyclic lipopeptides (CLPs) produced by Bacillus velezensis MEP2 18, a plant growth-promoting bacterium with high potential as a producer of bioactive molecules. Under optimized culture conditions MEP2 18 produces mostly C16-C17 fengycin (FENG) with well-characterized antibacterial activity against phytopathogens. The complete genome of MEP2 18 was sequenced and deposited on GenBank (CP042864). The antibacterial activity of CLPs and the FENG fraction produced by MEP2 18 was tested on Mueller-Hinton agar plates, by using the disk diffusion method, against clinically relevant bacteria including isolates from cystic fibrosis (CF) affected patients. To detect rapid changes in relative viability following exposure to FENG we employed the LIVE/DEAD® BacLightTM kit (Invitrogen) in combination with flow cytometry. The stability of FENG was evaluated under different pH and temperature conditions. The core genome of MEP2 18 consisted of 2659 CDS, while the pan-genome comprised 6291 CDS. Twentynine singletons specific to MEP2 18 were found in comparison with close related strains. The fengycin biosynthetic gene cluster (BGC) identified in MEP2 18 showed significant similarity to previously characterized fengycin BGC. This finding suggests a conserved genetic architecture and functional importance of the fengycin biosynthetic pathway. However, we observed frameshifts in the CDS of fenA and fenD within the fengycin BGC of MEP2 18. FENG was active against antibiotic-resistant hospital pathogenic bacteria (MDR) and its the antimicrobial activity was heat-stable and resistant to a wide range of pH. At the tested concentrations CLPs from MEP2 18 inhibited the growth of Acinetobacter baumannii Ab242, a clinical MDR strain, and FENG was identified as the active fraction. Other HPLC eluted fractions containing fengycins or other CLPs did not show antibacterial activity. The growth inhibition zones observed for FENG were comparable to those obtained with the hospitalused antibiotics Tobramycin and Ceftazidime. Growth inhibition zones produced by FENG were also observed for other MDR hospital pathogens such as Burkholderia spp. and Achromobacter spp. Flow cytometry assays showed an increase of dead cells stained with propidium iodide when A. xylosoxidans CAMPA 1650 was exposed to 20 µg/ml of FENG. In summary, the exclusive antibacterial property observed for FENG produced by MEP2 18, along with the frameshifts detected in fenA and fenD CDS, suggests a potential relationship between these genetic variations and the antimicrobial properties of FENG.