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Journal of Bacteriology, November 1998, p. 5921-5927, Vol. 180, No. 22
Department of Animal
Sciences1 and
School of Biological
Sciences,2 University of Nebraska, Lincoln,
Nebraska 68583-0908
Received 15 June 1998/Accepted 10 September 1998
The adherence of Ruminococcus albus 8 to crystalline
cellulose was studied, and an affinity-based assay was also used to
identify candidate cellulose-binding protein(s). Bacterial adherence in cellulose-binding assays was significantly increased by the inclusion of either ruminal fluid or micromolar concentrations of both
phenylacetic and phenylpropionic acids in the growth medium, and the
addition of carboxymethylcellulose (CMC) to assays decreased the
adherence of the bacterium to cellulose. A cellulose-binding protein
with an estimated molecular mass following sodium dodecyl
sulfate-polyacrylamide gel electrophoresis of ~21 kDa, designated
CbpC, was present in both cellobiose- and cellulose-grown cultures, and
the relative abundance of this protein increased in response to growth
on cellulose. Addition of 0.1% (wt/vol) CMC to the binding assays had
an inhibitory effect on CbpC binding to cellulose, consistent with the
notion that CbpC plays a role in bacterial attachment to cellulose. The nucleotide sequence of the cbpC gene was determined by a
combination of reverse genetics and genomic walking procedures. The
cbpC gene encodes a protein of 169 amino acids with a
calculated molecular mass of 17,655 Da. The amino-terminal third of the
CbpC protein possesses the motif characteristic of the Pil family of
proteins, which are most commonly involved with the formation of type 4 fimbriae and other surface-associated protein complexes in
gram-negative, pathogenic bacteria. The remainder of the predicted CbpC
sequence was found to have significant identity with 72- and
75-amino-acid motifs tandemly repeated in the 190-kDa surface antigen
protein of Rickettsia spp., as well as one of the major
capsid glycoproteins of the Chlorella virus PBCV-1.
Northern blot analysis showed that phenylpropionic acid and ruminal
fluid increase cbpC mRNA abundance in cellobiose-grown
cells. These results suggest that CbpC is a novel cellulose-binding
protein that may be involved in adherence of R. albus to
substrate and extends understanding of the distribution of the Pil
family of proteins in gram-positive bacteria.
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Adherence of the Gram-Positive Bacterium
Ruminococcus albus to Cellulose and Identification of a
Novel Form of Cellulose-Binding Protein Which Belongs to the Pil Family
of Proteins
*
Corresponding author. Mailing address: C220 AnS, Marvel
Baker Hall, East Campus, University of Nebraska
Lincoln, NE
68583-0908. Phone: (402) 472-9382. Fax: (402) 472-6362. E-mail:
ansc802{at}unlvm.unl.edu.
Journal series no. 11973, Agricultural Research Division,
University of Nebraska.
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