Based on Bacteroides thetaiotaomicron gene BT_4769, a conserved protein found in a conjugate transposon. As seem in gene expression experiments (http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE2231). It appears to be upregulated in the presence of host or other bacterial species vs when in culture [1,2].

1: Glycan foraging in vivo by an intestine-adapted bacterial symbiont. Sonnenburg JL, Xu J, Leip DD, Chen CH et al Science 2005 Mar 25;307(5717):1955-9. PMID:15790854

2: A hybrid two-component system protein of a prominent human gut symbiont couples glycan sensing in vivo to carbohydrate metabolism. Sonnenburg ED, Sonnenburg JL, Manchester JK, Hansen EE et al. Proc Natl Acad Sci U S A 2006 Jun 6;103(23):8834-9. PMID:16735464