Brian Sogaard Laursen

Antifouling enzymes and the biochemistry of marine settlement.

Antifouling coatings are used extensively on marine vessels and constructions, but unfortunately they are found to pose a threat to the marine environment, notably due to content of metal-based biocides. Enzymes have repeatedly been proposed as an alternative to traditional antifouling compounds. In this review, the enzymes claimed to hold antifouling activity are classified according to catalytic functions. The enzyme functions are juxtaposed with the current knowledge about the chemistry of settlement and adhesion of fouling organisms. Specific focus will be on bacteria, microalgae, invertebrate larvae and macroalgae zoospores. Two main concepts in enzyme-based antifouling are identified: breakdown of adhesive components and catalytic production of repellent compounds in-situ. The validity of the various modes of action is evaluated and the groups of enzymes with the highest potential are highlighted.

Biomimetic silica encapsulation of enzymes for replacement of biocides in antifouling coatings.

Current antifouling technologies for ship hulls are based on metals such as cuprous oxide and co-biocides like zinc pyrithione. Due to the persistent adverse environmental effects of these biocides, enzyme-based antifouling paints are proposed as a bio-based, non-accumulating alternative. Here, a hydrogen peroxide-producing system composed of hexose oxidase (HOX, EC 1.1.3.5), glucoamylase (GA, EC 3.2.1.3) and starch is tested for the chemical and physical functionalities necessary for successful incorporation into a marine coating. The activity and stability of the enzymes in seawater was evaluated at different temperatures, and paint compatibility was assessed by measuring the distribution and activity of the enzymes incorporated into prototype coating formulations. We used a biomimetic encapsulation procedure for HOX through polyethylenimine-templated silica co-precipitation. The co-precipitation and formulation of a powder for mixing into a marine paint was performed in a one-step economical and gentle formulation process, in which silica co-precipitated HOX was combined with GA and starch to form the antifouling system. Silica co-precipitation significantly improved the stability and performance of the antifouling system in marine-like conditions. For example, encapsulation of HOX resulted in 46% higher activity at pH 8, and its stability in artificial seawater increased from retaining only 3.5% activity after 2 weeks to retaining 55% activity after 12 weeks. A coating comprising the full enzyme system released hydrogen peroxide at rates exceeding a target of 36 nmol cm−2 d−1 for 3 months in a laboratory assay, and had potential for prolonged action through incorporation in a self-polishing coating.

Implementation of cross-linked enzyme aggregates of proteases for marine paint applications

Cross-linked enzyme aggregates (CLEAs) of proteases were tested in artificial seawater (ASW) both as it is and as a component of the paint. It is found that all CLEAs have tolerance to xylene and have great stability in dried paint. Moreover, CLEA Bacillus licheniformis shows 900% activation during the storage in ASW in dried paint.