BcsAB synthesized cellulose on nickel surface: polymerization of monolignols during cellulose synthesis alters cellulose morphology

The bacterial BcsA-B cellulose synthase synthesizes cellulose II when immobilized on nickel surfaces. To explore how lignin interacts with cellulose, lignin was polymerized either during or after cellulose formation from surface immobilized BcsA-B, leading to significant alterations in cellulose and lignin morphology. To facilitate lignin detection, polymerized coniferyl alcohol monolignols were detected by lignin autofluorescence. This compound was previously demonstrated as a suitable lignin monolignol exhibiting autofluorescence that enables lignin detection even at low concentrations. Cellulose and lignin coated nickel surfaces were studied under confocal microscopy, as well as by atomic force microscopy and X-ray diffractometry (XRD). As a consequence of simultaneous lignin and cellulose deposition on the surface, cellulose microfibril morphology was altered. XRD data indicated that cellulose crystal size was significantly decreased by polymerized lignin incorporation, suggesting that simultaneous lignin polymerization prevents the proper assembly of cellulose microfibrils. In contrast, polymerizing lignin after cellulose synthesis yielded a cellulose that was very similar in character to control (lignin-free) samples in terms of crystal morphology.