Aims: The goal of this study was to identify a marine algae-associated bacterium isolated from Laminaria japonica and investigate this microorganism's growth-promoting effects on plants. \ Methods and Results: The bacterium, identified as Pseudoalteromonas porphyrae, was determined to display a biostimulatory activity for seed germination and shoot growth in several agricultural plants and also for growth in ginseng callus cell culture. This biostimulatory activity was linked to a catalase enzyme that was excreted in the maximal amount during the transition from logarithmic growth phase to stationary growth phase. In addition, selected shifts in growth temperature and medium salinity affected the amount of enzyme excreted. The purified catalase was determined to he composed of identical subunits. The catalase of interest displayed significantly higher biostimulatory activity than the catalase from bovine liver. Conclusions: The catalase investigated in this study is unique in that it promotes growth in and possibly contributes to stress tolerance of Plants. Significance and Impact of the Study: The catalase of interest has the potential for use ill treatments that aim to improve percent seed germination as well as obtaining tall shoots in a shorter time period.