Role of contact in bacterial degradation of cellulose

Abstract Bacterial cells can adhere to cellulose fibres, but it is not known if cell-to-fibre contact is necessary for cellulose degradation. This problem was explored using aerobic cellulolytic bacteria, including known species and new isolates from soil. These were tested on plates containing Avicel, Solka floc, CF11 cellulose, carboxymethyl cellulose, or phosphoric acid-treated cellulose. Cellulose degradation was measured both by formation of clearing zones and by growth when cellulose was the only carbon source. The bacteria tested were either inoculated directly on the cellulose-containing agar, or separated from it by a pure agar layer or by membrane filters (not containing cellulose). Even when separated from the cellulose-containing agar all strains grew well. Clearing zones, best seen in phosphoric acid-treated cellulose, were larger under colonies separated from cellulose by an agar layer than under those in direct contact with cellulose. Such zones could also appear under filters. Our results show that bacterial degradation of cellulose does not depend on cell-to-fibre contact and suggest that when cellulose is at a greater distance from the cell, the removal of end products reduces catabolite repression of cellulose formation.