Efficient preparation of alginate oligosaccharides by using two thermostable alginate lyases and evaluation of the development promoting effects on Brassica napus L. in saline-alkali environment

Enzymatic degradation of alginate for the preparation of alginate oligosaccharides (AOS) is currently receiving significant attention in the field. AOS has been shown to promote crop growth and improve plant resistance to abiotic stresses. In this study, two novel PL6 family alginate lyases, AlyRm1 and AlyRm2, from Rhodothermus marinus DSM 4252, were expressed and characterized. These enzymes demonstrate exceptional activity and stable thermophilicity compared to other known alginate lyases. AlyRm1 (8855.34 U/mg) and AlyRm2 (7879.44 U/mg) exhibited excellent degradation activity towards sodium alginate even at high temperatures (70 °C). The AlyRm1 and AlyRm2 were characterized and utilized to efficiently produce AOS. The study investigated the promotional effect of AOS on the growth of Brassica napus L. seedlings in a saline-alkaline environment. The results of this study demonstrate the high activity and thermal stability of AlyRm1 and AlyRm2, highlighting their potential in the preparation of AOS. Moreover, the application of AOS prepared by AlyRm2 could enhance the resistance of Brassica napus L. to saline-alkali environments, thereby broadening the potential applications of AOS.