Evaluation of PHA production from the invasive macroalga Rugulopteryx okamurae

Resumen

Rugulopteryx okamurae is a brown macroalga listed as one of the most harmful invasive species by the European Union. This seaweed is mainly affecting the coasts of the Strait of Gibraltar but it is being spread to other areas rapidly. From a biorefinery point of view, macroalgae biomass is very interesting, mainly because it contains high amounts of carbohydrates and low lignin content. These characteristics make macroalgae a very interesting feedstock for the value-added compounds production such as polyhydroxyalkanoates (PHA), which are precursors of bioplastics. Herein, R. okamurae was subjected to thermoacid pretreatment and subsequent hydrolysis with a commercial enzyme cocktail Cellic Ctec2 at 50 ºC and 250 rpm. After that, the hydrolysate medium was used for PHA production with a pure culture of microorganisms (Cupriavidus necator). The growth of bacteria, consumption of reducing sugars and PHA production were continuously monitored throughout the process. In order to assess the potential of this macroalgae biomass for the PHA production, the fermentation profile was compared to that obtained using a synthetic standard medium. The results demonstrated that the biomass of R. okamurae shows an enormous potential as a raw material for producing a culture abundant in fermentable sugars and PHA. Specifically, almost 20 g/L of total reducing sugars were achieved after 24 h of enzyme hydrolysis. Furthermore, after 72 h of fermentation of C. necator, more than 61 % of the dry weight of the bacterial cells was PHA, clearly exceeding the 39 % obtained in the synthetic medium.