Functional heterologous expression of the biosynthetic genes for the cyanobacterial sulfated polysaccharide synechan in Synechococcus elongatus PCC 7942

Many sulfated polysaccharides (SPSs) possess useful physicochemical properties and biological activities and are widely used in industry. Currently, major SPSs are derived from livestock and marine organisms. To contribute to both the achievement of the Sustainable Development Goals and the development of diverse SPSs, microbial production systems are therefore needed. Nevertheless, bacteria capable of producing SPSs are limited. In contrast, many cyanobacteria synthesize diverse SPSs, making them promising hosts for the production of valuable SPSs, sources for novel SPSs, and genetic resources for SPS biosynthesis. However, no study has introduced an entire heterologous SPS biosynthetic system into cyanobacteria to produce a heterologous SPS. We recently identified a novel SPS, synechan, and elucidated the genetic basis for the biosynthesis and regulation of cyanobacterial SPSs. Here, we heterologously expressed the gene set responsible for synechan biosynthesis and its regulation in the non-SPS-producing cyanobacterium Synechococcus elongatus PCC 7942 and successfully induced the production of an SPS. Although the composition of the heterologously produced SPS differed from that of synechan and further optimization of the biosynthetic system is required, this work provides a foundation for engineering cyanobacteria to produce useful SPSs and for synthetic-biology-based functional analysis of previously uncharacterized SPS biosynthetic gene clusters.