Characterization of three biofilm-forming cyanobacteria and their potential in biotechnological applications.

Biofilms are complex-surface attached communities of both phototrophic (mainly cyanobacteria and microalgae) and heterotrophic microorganisms. There is an increasing interest in understanding how these communities operate, thanks not only to their ecological importance but also to their potential for biotechnological applications (Abed et al. 2009). Microalgae and cyanobacteria in fact, offer the possibility to couple sewage post-treatment with intensive production of biomass, suitable for the extraction of valuable compounds: microalgae, and recently cyanobacteria (Bruno et al. 2012) are considered to be promising feedstock for biofuels, being the productivity of these photosynthetic microorganisms in converting carbon dioxide into carbon-rich lipids highly competitive and sustainable respect to agricultural oleaginous crops (Mata et al. 2010). In addition there is an increasing interest in algal and cyanobacterial polysaccharides from food, pharmaceutical and biomedical industrial sectors. The majority of studies on algal mass cultures for wastewater treatment and bio-product purposes is focused on suspended microalgae, mainly grown in open or enclosed systems, where harvesting or removal of biomass can account for up to 30% of total costs (Wiffels and Barbosa 2010). In this study, three biofilm-forming cyanobacteria, isolated from a dystrophic (iper-eutrophic) coastal lagoon of Cabras (Oristano, Sardinia), were isolated and characterized by a polyphasic approach, involving microscopy observations, ecological investigation and gene sequencing. The isolates were grown in batch systems and in a semi-continuous flow incubator, specifically designed for biofilms development. The biomass produced by each isolate was then used to extract, quantify and characterize exopolysaccharides and lipids. Data obtained from the flow-lane incubator system would support a more economical and sustainable use of the benthic microorganisms for biomass production. All strains produced exopolysaccharides with differing ratios of hydrophobic and hydrophilic moieties depending on the species and the polysaccharide fraction (i.e., whether capsular or released). The produced lipids contained fatty acids suitable for a high-quality biodiesel production, showing high proportions of saturated and monounsaturated fatty acids. In this microcosm it was also possible to monitor the nutrient stripping ability of phototrophic benthic biofilms and in particular, their ability of nitrogen and phosphorus removal.