Isolation and antimicrobial activity of a lanosol derivative from Osmundaria serrata (Rhodophyta) and a visual exploration of its biofilm covering

A biologically active compound, lanosol ethyl ether (LEE), was isolated from Osmundaria serrata and its antimicrobial activity was determined against various terrestrial bacteria and fungi, and marine bacteria isolated from the surface of the seaweed. This is the first report of the presence of a lanosol derivative in O. serrata. The mean bacteriostatic and fungistatic activity of LEE was 0.27 ± 0.07 mg ml− 1 and the mean bactericidal and fungicidal activity was 0.69 ± 0.15 mg ml− 1. These values are comparable to the estimated concentration of LEE in the whole plant of 0.20 mg ml− 1. Extracts of O. serrata containing LEE also caused deformities in some bacteria that were tested. Biofilms cause the fouling of surfaces in the marine environment. The use of paints containing highly toxic metals to control their growth are ecologically harmful. Alternatives are required. The biofilm growing on the surface of this red seaweed was studied by light and scanning electron microscopy. A diverse biofilm was seen on O. serrata with bacteria even seen close to the meristematic tips of the plant. Further work is required to determine whether the concentration of the active compound in the tips is bactericidal.