Physicochemical and geroprotective comparison of Nostoc sphaeroides polysaccharides across colony growth stages and with derived oligosaccharides

Nostoc sphaeroides is a cyanobacterium traditionally used as food and medicine in the form of macrocolonies, the main supporting matrix of which is polysaccharides. Despite recent success in industrial-scale culture of colonial N. sphaeroides, biochemical and biofunctional information on the polysaccharides during colony production is lacking. Using a size-based colony growth profiling strategy, we show here that the high/low molecular weight ratio of the polysaccharides is significantly decreased while their Fourier-transform infrared absorptions remain unchanged. Importantly, monosaccharide compositions of all polysaccharides are similar to that of field colonies, indicating a comparable quality of the cultured colony products in terms of sugar composition. Subsequent experiments using free radical scavenging and Caenorhabditis elegans survival assays demonstrate both in vitro and in vivo antioxidant activities of the polysaccharides. Furthermore, the oligosaccharides prepared by partial acid hydrolysis are, like the polysaccharides, confirmed to increase oxidative survival and lifespan of C. elegans. The oligosaccharides, but not the polysaccharides, are further shown to ameliorate polyglutamine-mediated neurotoxicity and behavioral decline in a C. elegans model of proteotoxic stress, revealing their neuroprotective activity not shown by the polysaccharides. Consistently, several stress and proteostasis-associated genes are also found to be upregulated only by the oligosaccharides. Taken together, our results reveal distinct but also shared physicochemical and biofunctional properties of N. sphaeroides polysaccharides across colony growth stages and with derived oligosaccharides and also demonstrate the potentials of Nostoc oligosaccharides and thereby their parent polysaccharides as novel geroprotectors, including their beneficial effects on stress, lifespan, and age-related symptoms.

Automated summary

This study revealed distinct physicochemical and biofunctional properties of N. sphaeroides polysaccharides during colony growth stages, with a significant decrease in high/low molecular weight ratio. Both polysaccharides and oligosaccharides demonstrated antioxidant activities, while only oligosaccharides showed neuroprotective effects, suggesting their potential as novel geroprotectors. Additionally, oligosaccharides were found to upregulate stress and proteostasis-associated genes in C. elegans.