The ulvanolytic capacity of the seaweed associated bacterium Aliiglaciecola sp. SL4

Polysaccharide utilization loci (PULs) enable marine heterotrophic bacteria to access the complex carbohydrates that constitute a major reservoir of fixed carbon in seaweed biomass. Here, we identify and characterize two enzymes from a novel ulvan utilization locus (uPUL) from the genome of Aliiglaciecola sp. SL4 ( Gla SL4), an epiphytic bacterium isolated from an Ulva species of green macroalgae. Genome analysis revealed a dedicated ulvan degradation system encoding a suite of carbohydrate-active enzymes (CAZymes) and auxiliary enzymes predicted to carry out ulvan depolymerisation and downstream oligosaccharide processing. Biochemical validation of the polysaccharide lyase Gla PL25a and the unsaturated glycoside hydrolase Gla GH105 confirmed their activities and broader roles as key initiating enzymes in the ulvan utilization pathway. These findings provide experimental evidence linking a previously uncharacterized uPUL to ulvan degradation, advancing our understanding of marine carbon cycling and expanding the repertoire of enzymes available for algal biomass conversion and the generation of value-added ulvan oligosaccharides.