Inhibiting bacterial biofilm formation by stimulating c-di-GMP regulation using citrus peel extract from Jeju Island.

Biofilms consist of single or multiple species of bacteria embedded in extracellular polymeric substances (EPSs), which affect the increase in antibiotic resistance by restricting the transport of antibiotics to the bacterial cells. An alternative approach to treatment with antimicrobial agents is using biofilm inhibitors that regulate biofilm development without inhibiting bacterial growth. In this study, we found that citrus peel extract from Jeju Island (CPEJ) can inhibit bacterial biofilm formation. According to the results, CPEJ concentration-dependently reduces biofilm formation without affecting bacterial growth. Additionally, CPEJ decreased the production of extracellular polymeric substances but increased bacterial swarming motility. These results led to the hypothesis that CPEJ can reduce intracellular bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) concentration. The results showed that CPEJ significantly reduced the c-di-GMP level through increased phosphodiesterase activity. Altogether, these findings suggest that CPEJ as a biofilm inhibitor has new potential for pharmacological (e.g. drug and medication) and industrial applications (e.g. ship hulls, water pipes, and membrane processes biofouling control).

Synergistic control of membrane biofouling using linoleic acid and sodium hypochlorite.

Biofouling is a major operational problem in the reverse osmosis (RO) process, affecting the membrane performance. Although sodium hypochlorite (NaOCl) is used to chemically clean the biofouled membranes, high concentrations of NaOCl cause morphological and chemical damage to the RO membrane. The objective of this study is to enhance chemical cleaning efficiency by combining with a dispersion agent (linoleic acid, LA) that does not harm the RO membrane, to overcome the disadvantages of NaOCl. Biofilm cells were initially dispersed with LA treatment and biofouled layers were subsequently cleaned using NaOCl at low concentration. The optimized combination resulted in 3.9-4.4 times higher flux recovery efficiency than that with individual treatments. Furthermore, the combination decreased the volume and thickness of the biofilm as well as the amount of extracellular polymeric substances. Taken together, the combined treatment of LA and NaOCl significantly improves RO biofouling control.