Xylanase, an essential enzyme for breaking down xylan, faces limitations in its industrial applications due to the relatively low catalytic activity of the wild type. Directed evolution was used to enhance the catalytic efficiency of xylanase that originated from the Dickeya dadantii DCE-01. A xylanase variant (Xyn-ep) was obtained with improved catalytic activity by random mutant library employing two rounds of error-prone PCR. The results showed that the Xyn-ep demonstrated enzyme activity 1.6 times higher than that of wild-type xylanase. Sequencing analysis pinpointed key mutation sites at S159P, K212N, and N397S, respectively. Homology modeling was used to analyze the location of the mutation sites and to investigate the mechanism of the improved catalytic performance. The mutant Xyn-ep showed improved catalytic performance by error-prone PCR. Additionally, the increased flexibility of the loop of the mutant may contribute to the enhanced activity. These findings indicate that error-prone PCR is an effective method for enhancing enzyme activity and that the mutant Xyn-ep may be a new GH30 xylanase, being a potential candidate for industrial applications such as bast fiber bio-degumming, cotton bio-refinery, paper making, and so on.

This study is aimed at optimizing the extraction of Laminaria japonica polysaccharides (LJPs) and evaluating the in vitro effects of LJPs on the growth and preservation of lactic acid bacteria (LAB) and bifidobacteria strains commonly used in yogurt, including Lactobacillus bulgaricus , Streptococcus thermophilus , and Bifidobacterium lactis . Various extraction methods, such as hot water extraction, microwave, and ultrasonic and enzymatic‐assisted extraction, were employed. Response surface methodology (RSM) was used to optimize the extraction process. LAB and bifidobacteria strains were inoculated into culture media containing different concentrations of LJPs, and microbial counts were measured. The results showed that the highest LJP yield was achieved under the optimized conditions: microwave time of 6.69 min, enzyme addition of 2.77%, and a cellulase‐to‐pectinase ratio of 4:1. Within a certain range, LJPs remarkably promoted the growth of L. bulgaricus, S. thermophilus , and B. lactis by increasing the maximum biomass and prolonging their storage viability. Therefore, RSM was successfully applied to optimize the extraction of LJPs and to improve the extraction yield. Moreover, the application of LJPs enhanced the growth and preservation of LAB and bifidobacteria under in vitro conditions. Notably, LJPs extended the stationary phase and delayed the death phase of all three strains, and significantly improved their viability during refrigerated storage for up to 3 weeks. This study provides new insights and a theoretical basis for the development of LJPs as a potential functional additive to improve probiotic survival in fermented dairy products.