Sustainable Production of Biocompatible Antifouling Compounds

Abstract

Within this investigation a more environmentally friendly strategy was pursued to obtain antifouling compounds with higher biocompatibility based on the chemical defenses of sessile marine organisms. Marine algae and cyanobacteria have shown to be a good example of them representing actually a rich source of potential natural high value antifouling compounds. During this work, it was desired to evaluate or demonstrate the technical feasibility to obatain natural antifouling compounds using an approach through the development of a bioprocess. To achieve this goal it was necessary to aboard several involved aspects from the perspective of different disciplines such as microbiology, chemistry, and biochemical engineering. The brown alga Sargassum muticum and cyanobacteria Geitlerinema sp. were evaluated as producers of bioactive natural antibiofouling compounds and extractions methods were developed to get a preconcentration of these compounds into crude extracts. These experiments comprised a comparison of antimicrobial activity of culture medium extracts (from the cyanobacterial strain Flo1) obtained using two polymeric resins (AmberliteTM XAD-16 and XAD-1180) for pre-concentration of exometabolites as well as physiological studies relating growth with excretion of these bioactive compounds. Concerning to the first point, the yield of extraction of crude medium extract (mg of crude extract mL-1 of supernatant) was calculated for cultures of different ages and the two mentioned resins. In all the cases, it was found that the obtained culture media extracts of Geitlerinema sp. exhibited antimicrobial activity after one week of cultivation. The potential of these crude extracts as potential antifouling agent was demonstrated by the determination of their antimicrofouling activity upon a number of bacteria and fungi, using microdilution methods and taking as reference the chemical biocides TBTO (bis (tributyltin) oxide) and zinc pyrithione. The task to develop antifouling compounds from natural sources were supported by the establishment of analytical methods-(ESI) MS/MS, GC-FID, GC-MS) which enabled the identification and quantification of bioactive substances present in the crude extracts. Several exometabolites produced by Geitlerinema sp could be identified (harmane, norharmane and 4,4 -dihydroxybiphenyl). The synthesis of bioactive compounds with antimicrobial activity, excreted by marine organisms, strongly depends on their growth conditions, therefore also the effect of cultivation conditions of microorganisms on the production and excretion of antimicrobial metabolites have been investigated. To improve the light uptake rate from the photosyntetic cells a flat-photo bioreactor module for the cultivation of filamentous cyanobacteria was designed. It was evaluated the production of antimicrobial compounds using cyanobacterial cells forming a biofilm on the surface of a flat-fotobioreactor operating in batch-modus under different conditions of illumination. From these results, it can be concluded that the technical feasibility (basic design) for the continuous production of antifouling compounds from the culture of marine bacteria is possible, but it needs to be improved with respect to: (i) the stability on the production and excretion of the metabolites by the microorganisms, (ii) a better understanding the mechanisms that regulate their expression and (iii) the yield and grade of recovery during the separation of the compounds.