Towards a cyanobacterial biorefinery: Carbohydrate fingerprint, biocomposition and enzymatic hydrolysis of Nostoc biomass

Abstract

High investment costs have switched the perspective of cyanobacterial biorefinery concepts from biofuels towards approaches with multiple high-value products including residual biomass utilization. For the purpose of residual biomass utilization, this study investigated the biomass of several Nostoc strains. The saccharide profiles of the highly complex heteroglycans in seven Nostoc strains was elucidated. Besides neutral sugars, uronic acids, amino sugars, other substituted sugars as well as different methylated sugars and their methylation patterns were identified. Also, the biocomposition of the exemplary strains Nostoc sp. De1, Nostoc sp. Cc3, and Nostoc muscorum I was investigated totaling 77.4%, 91.8%, and 71.4% biomass, respectively. Ash and moisture made up 11–15%, lipids 2–2.7%, starch 1.4–8.4%, structural saccharides 12.6–16.8%, and protein 37.7–49.3%. While overall the detected masses were 28.6%–8.2% short to full recovery, many identified sugars could not be quantified. Further, different industry enzymes were tested on these three Nostoc strains for saccharification and solubilization. The highest saccharification results for all three strains were 36 mg g−1, 73 mg g−1, and 75 mg g−1 for Nostoc sp. De1, Nostoc sp. Cc3 and N. muscorum I, respectively. The obtained results demonstrate the extremely complex heteroglycans in Nostoc biomass as well as the difficulty for industrial utilization of these saccharides. Yet, the achieved biomass solubilization of 57%, 49%, and 56% for Nostoc sp. De1, Nostoc sp. Cc3, N. muscorum I, respectively could still allow for efficient biomass utilization.