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Isolation of a halotolerant poly(ε-caprolactone)-depolymerizing strain of Bacillus gibsonii from seaside soil
Summary
Researchers isolated Bacillus gibsonii strain KRICT-1 from seaside soil and demonstrated it can depolymerize poly(ε-caprolactone) plastic—a biodegradable polymer—even at 10% salinity, representing the first known PCL-degrading strain of this species capable of functioning in marine-like conditions. Halotolerant plastic-degrading bacteria like KRICT-1 could form the basis of bioremediation strategies targeting biodegradable microplastics that persist in saline coastal and marine environments.
Few studies have investigated the biodegradation of microplastics in marine environments. Microorganisms that can degrade microplastics in high-salinity conditions are sought after. Therefore, we aimed to isolate a halotolerant poly(ε-caprolactone) (PCL)-degrading bacterium for applications in biotechnology. The bacterium isolated from seaside soil was identified as Bacillus gibsonii via phylogenetic analysis based on 16S rRNA gene sequences and designated as KRICT-1. We tested whether the KRICT-1 strain showed halotolerance by determining the sodium chloride (NaCl) tolerance at various concentrations. The KRICT-1 strain showed growth at up to 10% NaCl on Luria–Bertani (LB) medium agar plates and 10% NaCl in liquid LB medium, indicating that KRICT-1 can grow and produce a PCL-depolymerizing enzyme under high-salt conditions. The KRICT-1 strain could depolymerize PCL with a PCL film weight loss of 2.82% at up to 10% NaCl concentration after cultivation of 7 weeks. KRICT-1 is the first strain of B. gibsonii which shows PCL-depolymerizing activity. Scanning electron microscopy and water contact angle results confirmed the degradation of PCL by the KRICT-1 strain. The extracellular enzyme produced by the KRICT-1 strain was stable over a wide range of temperatures (15–40 °C) and pH (7.0–9.5). This halotolerant PCL-degrading bacterium can be used in the degradation of biodegradable plastics present in saline soils, saline water, and wastewater.