Although strictly anaerobic, P. gingivalis, which is phylogenetically close to B. fragilis, can also survive in the presence

of atmospheric oxygen [29]. Significantly, two known virulence factors encoded by this organism, haemolysin (hem) and the cysteine protease gingipain A (rgpA), display elevated expression levels, 3.66-fold and 2-fold respectively, in the presence of atmospheric oxygen [30]. Thus it appears find protocol that cysteine protease gene expression in a related Bacteroidetes P. gingivalis is sensitive to environmental cues including oxygen. This study investigates how the expression of B. fragilis C10 protease genes responds to key changes in environmental stimuli, and thus indicates their potential involvement in pathogenesis and survival in the non-gut environs. In addition, expression analysis data is presented for a set of genes encoding newly identified and described C10 paralogues in B. thetaiotaomicron. Results Identification of a family of paralogous C10 protease genes in B. thetaiotaomicron By a combination of global Rucaparib homology-based approaches, supplemented by searching for active site motifs associated with cysteine protease activity, we identified 4 genes encoding homologues of the streptococcal C10 protease SpeB in the genome sequence of B. thetaiotaomicron strain VPI-5482. The genes were named btpA (BT2450), btpB (BT2219), btpC (BT2217)

and btpZ (BT2220) for B acteroides t hetaiotaomicron protease. Unlike btpA, the btpB

btpC and btpZ genes were found clustered together in the genome (Figure 1). The btp gene products ranged from 20.0% to 22.6% residue identity to SpeB, and 38.4% to 42.3% similarity (Table 1). The btp gene products were also found to share significant homology with the recently described [9] Bfp proteases of B. fragilis (18.3% to 27.6% identity and 38.4% to 49.8% similarity) (Table 1). Among the protein set, BtpA displayed the highest level of residue identity to Bfp1 and Bfp2, while BtpB, BtpC and BtpZ formed a separate cluster of related proteins (Figure 2(a)). Within this cluster, the most similar pair-wise alignment was between BtpB and BtpC, which were 54.3% identical and 2.5% similar (Figure 2(a) and Table 1). Figure 1 Schematic Tideglusib diagram of two C10 protease loci in B. thetaiotaomicron VPI-5482. The upper diagram represents the genomic region that includes btpA, the lower diagram the genomic region associated with the btp cluster. The proteases are represented by the larger open arrows. The propeptide region is represented by pale grey shading and the mature protease region by the darker grey. The white open arrows represent the stapostatin-like inhibitors. The black region at the 5’ end of each gene corresponds to the leader peptide encoding region of the gene. The co-ordinates for the region of the VPI-5482 are given by the numbers in italics above the DNA, the numbers in italics below the DNA are the intergenic distances.