Novel utilization of the seaweed-based deoxy sugars rhamnose and fucose by engineered Corynebacterium glutamicum.

Seaweed represents a potential sustainable carbon source for industrial biotechnology, yet the workhorse bacterium Corynebacterium glutamicum cannot naturally metabolize the deoxy sugars L-rhamnose and L-fucose, abundant in green and brown seaweed, respectively. Expanding its substrate range is crucial for sustainable bioprocessing, by enabling utilization of the available biomass. In this study, we engineered C. glutamicum to utilize L-rhamnose and L-fucose by introducing the Escherichia coli operons rhaBADM and fucIKUA, enabling growth on these sugars as sole carbon sources. To enhance growth, we evaluated various transport systems and identified the non-native fucose permease (FucP) as the most efficient for L-rhamnose uptake, and the native myo-inositol transporter 2 (IolT2) as optimal for L-fucose uptake. During L-rhamnose and L-fucose utilization, L-lactaldehyde is formed as a byproduct. We demonstrate that the native acetaldehyde dehydrogenase encoded by ald also exhibits lactaldehyde dehydrogenase activity, and that its overexpression enhances L-lactaldehyde utilization. Finally, cultivation on green and brown seaweed hydrolysates enabled the engineered strains to achieve increased biomass formation through consumption of the targeted deoxy sugars. This study expands the substrate spectrum of C. glutamicum through pathway engineering, transport optimization, and functional identification of a native lactaldehyde dehydrogenase. Growth and L-lysine production on seaweed hydrolysates highlights the potential of this approach for sustainable marine biomass valorization and bioproduction of value-added compounds.