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Cell-associated -amylases of butyrate-producing Firmicute bacteria from the human colon

Alan G. Ramsay

Rowett Research Institute, Greenburn Road, Bucksburn, Aberdeen AB21 9SB, UK

Correspondence
Karen P. Scott
k.scott{at}rri.sari.ac.uk

Selected butyrate-producing bacteria from the human colon that are related to Roseburia spp. and Butyrivibrio fibrisolvens showed a good ability to utilize a variety of starches for growth when compared with the Gram-negative amylolytic anaerobe Bacteroides thetaiotaomicron. A major cell-associated amylase of high molecular mass (140–210 kDa) was detected in each strain by SDS-PAGE zymogram analysis, and genes corresponding to these enzymes were analysed for two representative strains. Amy13B from But. fibrisolvens 16/4 is a multi-domain enzyme of 144.6 kDa that includes a family 13 glycoside hydrolase domain, and duplicated family 26 carbohydrate-binding modules. Amy13A (182.4 kDa), from Roseburia inulinivorans A2-194, also includes a family 13 domain, which is preceded by two repeat units of 116 aa rich in aromatic residues, an isoamylase N-terminal domain, a pullulanase-associated domain, and an additional unidentified domain. Both Amy13A and Amy13B have N-terminal signal peptides and C-terminal cell-wall sorting signals, including a modified LPXTG motif similar to that involved in interactions with the cell surface in other Gram-positive bacteria, a hydrophobic transmembrane segment, and a basic C terminus. The overexpressed family 13 domains showed an absolute requirement for Mg²⁺ or Ca²⁺ for activity, and functioned as 1,4--glucanohydrolases (-amylases; EC 3.2.1.1). These major starch-degrading enzymes thus appear to be anchored to the cell wall in this important group of human gut bacteria.

The GenBank/EMBL/DDBJ accession numbers for the nucleotide sequences encoding the -amylases of Butyrivibrio fibrisolvens and Roseburia inulinivorans are AJ578026 and AM055811, respectively.

Present address: Centre for Tumour Biology, Institute of Cancer and CR-UK Clinical Centre, Bart's and The London Queen Mary's School of Medicine and Dentistry, John Vane Science Centre, Charterhouse Square, London EC1M 6BQ, UK.

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