Discovery of antimicrobial activity in chemical extracts derived from unexplored algal-bacterial culture systems and isolates

Abstract

Global health is affected by viral, bacterial, and fungal infections that cause chronic and often fatal diseases. Identifying novel antimicrobials through innovative methods that are active against human pathogens will create a new, necessary pipeline for chemical discovery and therapeutic development. Our goal was to determine whether algal production systems represent fertile ground for discovery of antibiotics and antifungals. To this end, we collected high-biomass algal-bacterial samples from outdoor mass cultivation systems, 18-L outdoor algal open cultures mesocosms, and non-axenic laboratory samples. We also cultivated 33 marine bacterial isolates for chemical extraction. Ultimately, we filtered, concentrated, extracted, and screened 77 chemically-complex mixtures using a conventional agar-based microbial growth inhibition assay against three microbes: Escherichia coli, Bacillus subtilis, and Candida albicans. We discovered that 23 of our chemical extracts (almost one-third of the chemical samples tested) exhibited some degree of growth inhibition toward B. subtilis and/or C. albicans. Our work here demonstrates the feasibility and potential of isolating bioactive natural products from high-biomass algal-bacterial samples from algal mass cultivation systems.

Keywords: Algal mass cultivation systems; Algal production systems; Antifungal; Antimicrobial; Microbial consortia; Natural products.

Fig. 1

Growth sensitivity exhibited by B. subtilis, C. albicans, and E. coli to tested chemical extracts. (A) Representative agar plates for each organism with positive control in upper right quadrant labeled “+” and “Pos con”, empty disk located in the plate center, and three tested extracts per plate with corresponding number labels. Chemical extracts resulting in distinguishable growth sensitivity to each microorganism are shown in (B), (C), and (D). A negative disk, labeled “NEG”, as an example of no exhibited growth sensitivity is shown in (C) for extract 47. Process control (chemical extract 67) results for B. subtilis and E. coli are labeled and shown in (A), (B), and (D).