Screening of Antibacterial Activity from Bacteria Associated with the Seaweeds Ulva sp. and Chaetomorpha sp. from Gunungkidul Coast, Indonesia

Abstract

Seaweed is a strategic multi-industry commodity for food, pharmaceuticals, and cosmetics. The multifunctional properties of seaweed are influenced not only by its nutritional and bioactive content but also by microbes associated with it, both on the surface and as endophytes within its tissues, thus forming a functional holobiont unit. These microbes actively affect the metabolism, morphology, and bioactive compound content which determine seaweed quality for food, medicine, and cosmetics. This study explored bacteria associated with seaweed from Gunungkidul Coast, Indonesia, such as Ulva sp. and Chaetomorpha sp. The aim of this research was to obtain bacteria associated with Ulva sp. and Chaetomorpha sp. that possess antibacterial activity against the pathogenic Escherichia coli and Staphylococcus aureus. Bacterial isolation was performed using the pour plate technique on de Man Rogosa Sharpe Agar (MRSA), Potato Dextrose Agar (PDA), Tryptic Soy Agar (TSA), Zobbel Marine Agar (ZMA), International Streptomyces Project-2 (ISP-2), and International Streptomyces Project-4 (ISP-4) media. Based on the number of colonies that grew, TSA medium was the most optimal, yielding 192 and 357 colonies from Ulva sp. and Chaetomorpha sp., respectively. Antibacterial testing showed that isolates U1 and U2 from Ulva sp. produced the largest inhibition zones, namely 12.71 mm and 5.27 mm against E. coli and 2 mm and 3.07 mm against S. aureus. Further testing of the cell-free supernatant (CFS) showed that these isolates were only active in inhibiting the growth of E. coli. Further genomic and metabolomic studies are needed to reveal more of the potential of bacteria from Ulva sp. as antibacterial agents in the food and pharmaceutical fields..