Chiang Mai Journal of Science

     A cost-effective strategy for superfine bacterial nanocellulose (BNC) production was successfully developed by the low-nutrient adaptive mutation. Two adapted strains, RC30-15 and RC37-23 were obtained from revertant strain R37-9 of Komagataeibacter oboediens MSKU 3 by a repetitive static cultivation at 30°C and 37°C, respectively. The repetitive cultivation was carried out in coconut water (CW) containing 1% acetic acid and 2% ethanol (CW1A2E), CW1A2E containing 0.5% sucrose (CW1A2E0.5S) and CW1A2E0.5S containing 0.5% ammonium sulfate (CW1A2E0.5S0.5N) for 30 passages (210 days). Strain R37-9 produced relatively low amount of superfine BNC of 0.71, 0.88 and 0.82 g/L dry weight after 7 days static cultivation at 37°C in CW1A2E, CW1A2E0.5S and CW1A2E0.5S0.5N, respectively. Two adapted strains exhibited higher BNC producing ability in coconut water than strain R37-9. Strains RC30-15 and RC37-23 produced the highest BNC yields of 3.63 and 8.22 g/L dry weight in CW1A2E0.5S and CW1A2E0.5S0.5N under static cultivation at 30°C and 37°C, respectively. SEM images of the nanofibrils produced from strain RC37-23 showed the finer nanocellulose fibrils and narrower range (24±0.47-34±0.81 nm) of fibril width compared with other strains. Furthermore, the density, moisture content and porosity of nanocellulose fibrils produced from strain RC37-23 in CW1A2E0.5S0.5N medium at 37°C exhibited the highest density (0.86±0.02 g/cm³) and moisture content (12.51±1.87 %). BNC from strain RC37-23 grown in CW1A2E0.5S0.5N medium at 37°C also possessed the lowest porosity (42.59±1.70%). It could be concluded that low-nutrient adapted strain at 37°C, strain RC37-23, produced not only the highest amount of BNC but also the better physicochemical properties of nanocellulose fibrils.