The genetic manipulation of rumen bacteria with special reference to fibre digestion

Expression of a cloned cellulase/xylanase gene from Prevotella ruminicola in Bacteroides vulgatus, Bacteroides uniformis and Prevotella ruminicola

A new shuttle vector, pRH3 (8.7 kb), was constructed for use in Prevotella/Bacteroides host strains. This vector combines the pRRI2 replicon from P. ruminicola, pBluescript sequences and a tetQ marker gene for selection in Prevotella/Bacteroides hosts. Following insertion of a fragment carrying an endoglucanase/xylanase gene from P. ruminicola 23 into the multiple cloning site, the resulting construct, pRH3X, was introduced into B. vulgatus 1447, B. uniformis 1100 and P. ruminicola 2202. This resulted in increases of between 4 and 50-fold in CM-cellulase and xylanase activities in cells grown with glucose. In contrast activities were barely detectable for the same construct in E. coli DH5 alpha. Most of the total xylanase activity produced was found within the cell in P. ruminicola 2202 and B. vulgatus 1447 transformed with pRH3X, and in P. ruminicola 23. An osmotic shock experiment indicated that a significant proportion of the xylanase activity in B. vulgatus 1447 cells carrying pRH3X was periplasmic.

DNA sequence and transcription of an endoglucanase gene from Prevotella (Bacteroides) ruminicola AR20

The endoglucanase gene was sequenced from Prevotella ruminicola AR20, isolated as clone pJW4. The endoglucanase (BrEND) is encoded by an open reading frame (ORF1) of 501 codons, corresponding to a protein of calculated molecular weight 55.7 kDa. Analysis of proteins on SDS-PAGE revealed a protein corresponding to the calculated molecular weight of the processed BrEND. The protein showed substantial homology to members of the A4 sub-family cellulases. Primer extension studies revealed that transcription of celA is initiated at different sites in Escherichia coli and Prevotella ruminicola. E. coli sigma 70 recognition sequences were identified, which were located upstream from the transcription initiation site (TIS) functional in E. coli. A longer extension product was identified using RNA from P. ruminicola, indicating that the gene may normally be transcribed as part of a polycistronic message. The end of the primer extension product corresponded to a site beyond the 5' boundary of the cloned fragment, thus preventing identification of native promoter sequences. A second ORF of 110 codons (ORF2) was identified on the antisense strand, and primer extension indicated that transcription through ORF2 was initiated at an identical site in both E. coli and P. ruminicola. E. coli-like consensus sequences were located at positions -10 and -35 upstream from this site, suggesting that some promoter sequences in P. ruminicola are similar to E. coli consensus sequences, although others recognized by E. coli are non-functional in P. ruminicola.(ABSTRACT TRUNCATED AT 250 WORDS)