title: Evidence for lignin oxidation by the giant panda fecal microbiome.
abstract: The digestion of lignin and lignin-related phenolic compounds from bamboo by giant pandas has puzzled scientists because of the lack of lignin-degrading genes in the genome of the bamboo-feeding animals. We constructed a 16S rRNA gene library from the microorganisms derived from the giant panda feces to identify the possibility for the presence of potential lignin-degrading bacteria. Phylogenetic analysis showed that the phylotypes of the intestinal bacteria were affiliated with the phyla Proteobacteria (53%) and Firmicutes (47%). Two phylotypes were affiliated with the known lignin-degrading bacterium Pseudomonas putida and the mangrove forest bacteria. To test the hypothesis that microbes in the giant panda gut help degrade lignin, a metagenomic library of the intestinal bacteria was constructed and screened for clones that contained genes encoding laccase, a lignin-degrading related enzyme. A multicopper oxidase gene, designated as lac51, was identified from a metagenomic clone. Sequence analysis and copper content determination indicated that Lac51 is a laccase rather than a metallo-oxidase and may work outside its original host cell because it has a TAT-type signal peptide and a transmembrane segment at its N-terminus. Lac51 oxidizes a variety of lignin-related phenolic compounds, including syringaldazine, 2,6-dimethoxyphenol, ferulic acid, veratryl alcohol, guaiacol, and sinapinic acid at conditions that simulate the physiologic environment in giant panda intestines. Furthermore, in the presence of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), syringic acid, or ferulic acid as mediators, the oxidative ability of Lac51 on lignin was promoted. The absorbance of lignin at 445 nm decreased to 36% for ABTS, 51% for syringic acid, and 51% for ferulic acid after incubation for 10 h. Our findings demonstrate that the intestinal bacteria of giant pandas may facilitate the oxidation of lignin moieties, thereby clarifying the digestion of bamboo lignin by the animal.
authors.affiliation: School of Life Sciences, Anhui University, Hefei, Anhui, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Fang
authors.forename: Zemin
authors.initials: Z
authors.lastname: Fang
authors.forename: Peng
authors.initials: P
authors.lastname: Zhou
authors.forename: Fei
authors.initials: F
authors.lastname: Chang
authors.forename: Yuzhi
authors.initials: Y
authors.lastname: Hong
authors.forename: Xuecheng
authors.initials: X
authors.lastname: Zhang
authors.forename: Hui
authors.initials: H
authors.lastname: Peng
authors.forename: Yazhong
authors.initials: Y
authors.lastname: Xiao
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003300:Copper / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D005243:Feces; D015723:Gene Library; D007422:Intestines / Q000382:microbiology; D042845:Laccase / Q000737:chemistry* / Q000378:metabolism; D008031:Lignin / Q000378:metabolism*; D054892:Metagenome; D056186:Metagenomics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010088:Oxidoreductases / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D019800:Phenol / Q000737:chemistry; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D011549:Pseudomonas / Q000378:metabolism; D012336:RNA, Ribosomal, 16S / Q000378:metabolism; D031787:Sasa; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D001503:Ursidae
chemical_list: D012336:RNA, Ribosomal, 16S; D019800:Phenol; D003300:Copper; D008031:Lignin; D010088:Oxidoreductases; D042845:Laccase; C024748:copper oxidase; D010100:Oxygen