Xanthomonas campestris pv. campestris secretes the endoglucanases ENGXCA and ENGXCB: construction of an endoglucanase-deficient mutant for industrialxanthan production

Xanthomonas campestris pv. campestris secretes at least two cellulose-degra ding endoglucanases. One of these endoglucanases is encoded by the engXCA g ene of X. c. pv. campestris 8400 that was previously characterized by Gough et al. [Gene (1990) 89: 53-59]. An additional endoglucanase encoded by the engXCB gene was identified in X. c. pv. campestris 8400 and FC2. The engXC B gene product that was grouped into the endoglucanase family E contains a putative N-terminal signal peptide, suggesting a secretion by the type II s ecretion system. The ENGXCB protein contributed approximately 8% to the cel lulase activity in xanthan preparations. Deletion of engXCA and engXCB resu lted in a fivefold reduction of the cellulose-degrading activity in xanthan preparations. The cellulase activity determined in xanthan preparations of the engXCA-engXCB mutant was only slightly higher than the activity found in preparations that were subjected to heat treatment. Mutations in engXCA and engXCB did not affect the growth rate and xanthan production of X. c. p v. campestris FC2 under several cultivation conditions. The engXCA-engXCB d eletion mutant is markerless, which makes this mutant a valuable strain for xanthan production and approaches aimed at inactivating further genes enco ding extracellular enzymes.