Affiliation:
1. Tuklas Lunas Development Center, University of San Carlos, Cebu City 6000, Philippines
2. Applied Microbiology and Molecular Biology Laboratory, Department of Biology, University of San Carlos, Cebu City 6000, Philippines
Abstract
Halymenia durvillei is a red alga that is commonly utilized in the Philippines as food and as a source of high-value natural products for industrial applications. However, there are no studies regarding the microbial community associated with H. durvillei and its potential applications. This study aimed to isolate and identify the epiphytic bacteria of H. durvillei and determine their antimicrobial and quorum sensing inhibitory (QSI) effects. The thalli of H. durvillei were collected at the shores of Santa Fe, Bantayan, Cebu, Philippines. Bacterial isolates were identified using 16S rRNA, and their ethyl acetate (EtOAc) extracts were subjected to antimicrobial susceptibility tests against representative species of yeast and Gram-negative and Gram-positive bacteria. Their QSI activity against
Chromobacterium violaceum
was also determined. Fourteen distinct bacterial colonies belonging to four genera, namely
Alteromonas
(3),
Bacillus
(5),
Oceanobacillus
(1) and
Vibrio
(5), were successfully isolated and identified. All 14 bacterial isolates exhibited antibacterial effects. EPB9, identified as
Bacillus safensis
, consistently showed the strongest inhibition against
Escherichia coli
,
Staphylococcus aureus
and
Staphylococcus epidermidis
, with minimum inhibitory concentrations (MICs) ranging from 0.0625 to 1.0 mg ml−1. In contrast, all 14 isolates showed weak antifungal effects. Both
B. safensis
(EPB9) and
Bacillus australimaris
(EPB15) exhibited QSI effects at 100 mg ml−1, showing opaque zones of 3.1±0.9 and 3.8±0.4 mm, respectively. This study is the first to isolate and identify the distinct microbial epiphytic bacterial community of H. durvillei and its potential as an abundant resource for new antibacterial and QSI bioactives.
Funder
Philippine Council for Agriculture, Aquatic and Natural Resources Research and Development
Subject
Microbiology (medical),Microbiology