Alteromonas macleodii Dow02-2 is provided, wherein the Alteromonas macleodii Dow02-2 was deposited at German Collection of Microorganisms and Cell Cultures (Deutsche Sammlung von Mikroorganismen and Zellkulturen, DSMZ) under the accession number DSM33380, and its metabolites comprise 2-hydroxy-3-methylbutyric acid. A method for providing 2-hydroxy-3-methylbutyric acid is also provided, wherein the method comprises isolating the 2-hydroxy-3-methylbutyric acid from metabolites of Alteromonas macleodii Dow02-2 of biologically pure culture. A method for at least one of increasing expression of TGM1 gene, increasing expression of KRT1 gene, increasing expression of KRT10 gene, increasing expression of KRT14 gene, increasing expression of FLG gene, increasing expression of GBA gene, and increasing expression of HAS3 gene is also provided, wherein the method comprises administering to a subject in need thereof an effective amount of 2-hydroxy-3-methylbutyric acid.