Characterization of alginate-degrading bacteria isolated from seaweed-producing areas of South Korean territory and verification of the bacteria as plant growth-promoting biofertilizer

Alginate, a carbohydrate polymer produced by seaweed and some bacteria, is widely used in the food and medicine industries. Alginate oligosaccharides, produced by depolymerizing alginate, exhibit diverse biological functions, such as plant protection and growth promotion, enhancement of microbial metabolic activity, and potential applications in biofuel production. This study isolated 13 alginate-degrading bacterial strains from over a thousand seaside soil bacteria in South Korea and investigated their alginate-degrading characteristics. Through 16S rDNA sequencing, <i>Marinomonas sp</i>., <i>Zobellella sp</i>., and <i>Pseudomonas sp</i>. were newly identified at the subspecies level. Notably, this study is the first to report the alginate-degrading capability of <i>Zobellella sp</i>. The substrate specificity of each bacterial strain was analyzed toward poly-α-L-guluronate and poly-β-D-mannuronate, the two major alginate polymeric components. Furthermore, 3 of the 13 isolated strains were demonstrated to synthesize auxin, and their application to <i>Arabidopsis thaliana</i> confirmed enhanced vegetative growth. These findings advance our understanding of alginate degradation and highlight the potential of these bacteria and their alginate lyases as valuable resources in biotechnology applications. In addition, the potential of these bacteria as biofertilizers for promoting plant growth and the production of functional alginate oligosaccharides underscores the need for further exploration and development in this field.IMPORTANCEThis study aimed to isolate alginate-degrading bacteria from the soil samples collected in South Korea's major seaweed production areas and evaluate their potential as biofertilizers. Alginate, a primary component of brown algae, breaks down into alginate oligosaccharides, which are known to enhance plant growth. In this study, 13 strains of alginate-degrading bacteria were isolated, and some of them showed the potential for plant growth promotion and stress defense through strong biofilm formation and auxin production. Importantly, these bacterial strains exhibited plant growth-promoting potential, demonstrating their applicability in combination with seaweed-based fertilizers. These findings provide valuable insights that could broaden the industrial utilization of seaweed-derived fertilizers, contributing to enhanced agricultural productivity and sustainability.