title: Genetic and biochemical approaches towards unravelling the degradation of gallotannins by Streptococcus gallolyticus.
abstract: BACKGROUND
  Herbivores have developed mechanisms to overcome adverse effects of dietary tannins through the presence of tannin-resistant bacteria. Tannin degradation is an unusual characteristic among bacteria. Streptococcus gallolyticus is a common tannin-degrader inhabitant of the gut of herbivores where plant tannins are abundant. The biochemical pathway for tannin degradation followed by S. gallolyticus implies the action of tannase and gallate decarboxylase enzymes to produce pyrogallol, as final product. From these proteins, only a tannase (TanBSg) has been characterized so far, remaining still unknown relevant proteins involved in the degradation of tannins.
  
  
  RESULTS
  In addition to TanBSg, genome analysis of S. gallolyticus subsp. gallolyticus strains revealed the presence of an additional protein similar to tannases, TanASg (GALLO_0933). Interestingly, this analysis also indicated that only S. gallolyticus strains belonging to the subspecies "gallolyticus" possessed tannase copies. This observation was confirmed by PCR on representative strains from different subspecies. In S. gallolyticus subsp. gallolyticus the genes encoding gallate decarboxylase are clustered together and close to TanBSg, however, TanASg is not located in the vicinity of other genes involved in tannin metabolism. The expression of the genes enconding gallate decarboxylase and the two tannases was induced upon methyl gallate exposure. As TanBSg has been previously characterized, in this work the tannase activity of TanASg was demonstrated in presence of phenolic acid esters. TanASg showed optimum activity at pH 6.0 and 37°C. As compared to the tannin-degrader Lactobacillus plantarum strains, S. gallolyticus presented several advantages for tannin degradation. Most of the L. plantarum strains possessed only one tannase enzyme (TanBLp), whereas all the S. gallolytcius subsp. gallolyticus strains analyzed possesses both TanASg and TanBSg proteins. More interestingly, upon methyl gallate induction, only the tanB Lp gene was induced from the L. plantarum tannases; in contrast, both tannase genes were highly induced in S. gallolyticus. Finally, both S. gallolyticus tannase proteins presented higher activity than their L. plantarum counterparts.
  
  
  CONCLUSIONS
  The specific features showed by S. gallolyticus subsp. gallolyticus in relation to tannin degradation indicated that strains from this subspecies could be considered so far the best bacterial cellular factories for tannin degradation.
authors.affiliation: Laboratorio de Biotecnología Bacteriana, Instituto de Ciencia y Tecnología de Alimentos y Nutrición, ICTAN-CSIC, Juan de la Cierva 3, Madrid, Spain. nataliajm@ictan.csic.es.
authors.forename: Natalia
authors.initials: N
authors.lastname: Jiménez
authors.affiliation: Laboratorio de Biotecnología Bacteriana, Instituto de Ciencia y Tecnología de Alimentos y Nutrición, ICTAN-CSIC, Juan de la Cierva 3, Madrid, Spain. imreveron@ictan.csic.es.
authors.forename: Inés
authors.initials: I
authors.lastname: Reverón
authors.affiliation: Laboratorio de Biotecnología Bacteriana, Instituto de Ciencia y Tecnología de Alimentos y Nutrición, ICTAN-CSIC, Juan de la Cierva 3, Madrid, Spain. mariaet@ictan.csic.es.
authors.forename: María
authors.initials: M
authors.lastname: Esteban-Torres
authors.affiliation: Laboratorio de Biotecnología Bacteriana, Instituto de Ciencia y Tecnología de Alimentos y Nutrición, ICTAN-CSIC, Juan de la Cierva 3, Madrid, Spain. fxlopez@ictan.csic.es.
authors.forename: Félix
authors.initials: F
authors.lastname: López de Felipe
authors.affiliation: Laboratorio de Biotecnología Bacteriana, Instituto de Ciencia y Tecnología de Alimentos y Nutrición, ICTAN-CSIC, Juan de la Cierva 3, Madrid, Spain. blanca.r@csic.es.
authors.forename: Blanca
authors.initials: B
authors.lastname: de Las Rivas
authors.affiliation: Laboratorio de Biotecnología Bacteriana, Instituto de Ciencia y Tecnología de Alimentos y Nutrición, ICTAN-CSIC, Juan de la Cierva 3, Madrid, Spain. r.munoz@csic.es.
authors.forename: Rosario
authors.initials: R
authors.lastname: Muñoz
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002262:Carboxy-Lyases / Q000235:genetics / Q000378:metabolism; D002265:Carboxylic Ester Hydrolases / Q000235:genetics / Q000378:metabolism; D016680:Genome, Bacterial; D047348:Hydrolyzable Tannins / Q000378:metabolism*; D013291:Streptococcus / Q000201:enzymology / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D047348:Hydrolyzable Tannins; D002265:Carboxylic Ester Hydrolases; C022711:tannase; D002262:Carboxy-Lyases