Thermostable and alkaline-or acid-stable xylanases are more advantageous in agricultural and industrial fields. In this study, a rational structure-based design was conducted based on a thermostable GH11 xylanase TlXynA from Thermomyces lanuginosus to improved pH-tolerance. Four mutant enzymes (P1, P2, P3, and P4) and five variants (N1, N2, N3, N4, and N5) were constructed by substituting surface charged residue combinations using site-directed mutagenesis. Compared to the native enzyme, two mutants P1 and P2 showed higher acid tolerance, especially at pH 3.0, presented 50 and 40% of their maximum activity, respectively. In addition, four mutants N1, N2, N3 and N4 had higher tolerance than the native enzyme to alkaline environments (pH 7.0-9.0). At pH 9.0, the residual activities of N1, N2, N3, and N4 were 86, 78, 77, and 66%, respectively. In summary, an improved pH-tolerance design principle is being reported.

Brown macroalgae have attracted great attention as an alternative feedstock for biorefining. Although direct conversion of ethanol from alginates (major components of brown macroalgae cell walls) is not amenable for industrial production, significant progress has been made not only on enzymes involved in alginate degradation, but also on metabolic pathways for biorefining at the laboratory level. In this article, we summarise recent advances on four aspects: alginate, alginate lyases, different alginate-degrading systems, and application of alginate lyases and associated pathways. This knowledge will likely inspire sustainable solutions for further application of both alginate lyases and their associated pathways.

Strains J15B81-2T and J15B91T were isolated from a sediment sample collected from the South China Sea. Cells of both strains were observed to be rod-shaped, non-gliding, Gram-stain-negative, yellow-pigmented, facultatively anaerobic, catalase-positive, oxidase-negative and showing optimum growth at 30 °C. Strains J15B81-2T and J15B91T could tolerate up to 9 and 10  % (w/v) NaCl concentration and grow at pH 6.5–9.5 and 6.0–9.0, respectively. The strains shared 97.4 % 16S rRNA gene sequence similarity to each other but were identified as two distinct species based on 81.1–85.8 % ANIb and 31.5 % dDDH values calculated using whole genome sequences. Strains J15B81-2T and J15B91T shared highest 16S rRNA gene sequence similarity to Salinimicrobium xinjiangense CGMCC 1.12522T (98.4 %) and Salinimicrobium sediminis CGMCC 1.12641T (98.0 %), respectively. Among species with validly published names, S. sediminis CGMCC 1.12641T shared close genetic relatedness with strains J15B81-2T [85.1–85.3% average nucleotide identity based on blastBlast+ (ANIb) and 30.6 % digital DNA–DNA hybridization (dDDH)] and J15B91T (76.6–79.1 % ANIb and 21.5 % dDDH). The major fatty acid of strains J15B81-2T and J15B91T were identified as iso-C15 : 0 and iso-C16 : 0, respectively, and the major polar lipids of the two strains consisted of phosphatidylethanolamine, one unidentified phospholipid, one unidentified aminolipid and one unidentified lipid. The strains contained MK-6 as their predominant menaquinone. The genomic G+C contents of strains J15B81-2T and J15B91T were determined to be 41.7 and 41.8 mol %, respectively. Both strains are considered to represent two novel species of the genus Salinimicrobium and the names Salinimicrobium nanhaiense sp. nov. and Salinimicrobium oceani sp. nov. are proposed for strains J15B81-2T (=KCTC 72867T=MCCC 1H00410T) and J15B91T (=KCTC 72869T=MCCC 1H00411T), respectively.