Fig. 1

Screening of the L. japonica-decomposing bacterial strain Pseudoalteromonas agarivorans A3. A the degradation of alginate by strain A3. Strain A3 was cultured on the screening plate at 25 °C for 5 days and the plate were dyed with Lugol’s solution to determine the degradation of alginate around the strain colony. B the growth curve of strain A3 cultured in the liquid medium containing 0.5% sodium alginate as the sole carbon source. The growth curve of strain A3 cultured in the liquid medium without sodium alginate was taken as the control. C decomposition of L. japonica by strain A3. Strain A3 was cultured at 25 °C in the medium containing a piece of L. japonica blade and 3% sea salts. The decomposition of L. japonica was observed at 0, 6, 12 and 24 h. The L. japonica blade-containing medium without strain A3 incubated at 25 °C, 180 rpm for 24 h was taken as the control. D the neighbor-joining phylogenetic tree of strain A3 based on the 16S rRNA gene sequences. The bootstrap values of each branch were tested by 1000 repetitions. E transmission electron micrograph of negatively stained cells of strain A3 cultured in 2216E marine broth at 25 °C for 12 h. F LTQ-Orbitrap-MS analysis of the degradation products of the L. japonica piece by the fermentation broth supernatant of strain A3. DP degree of polymerization, AO alginate oligosaccharide