Identification of nitrogen-fixing bacteria on green tide-causing species and evaluation of their nitrogen-fixing...

Different algae host distinct phycosphere microenvironments, where mutualistic relationships between algae and symbiotic and epiphytic bacteria are common. Ulva prolifera (U. prolifera) harbors a diverse microbial community that plays a crucial role in its morphogenesis and growth. In this study, 28 bacterial strains were isolated from U. prolifera using 2216E medium. Molecular identification via the nifH gene (nitrogenase coding gene) revealed that three of these strains harbored the nifH gene, all belonging to the genus Cobetia. When co-cultured with sterile U. prolifera for 31 days, the results indicated that these nitrogen-fixing bacteria significantly enhanced the growth of U. prolifera. Nitrogenase activity was quantified, which demonstrated that these bacteria supplied nitrogen to U. prolifera through biological nitrogen fixation, thus promoting its growth. This study demonstrates that there are indeed microorganisms with nitrogen-fixing ability on the U. prolifera, which provide nitrogen for U. prolifera and significantly promote its growth.