Strain improvement and statistical optimization as a combined strategy for improving fructosyltransferase production by NAC8.

Strain improvement of a low fructosyltransferase-producing NAC8 (Accession No. KX023301) was carried out using chemical mutagens such as ethidium bromide and ethyl methane sulfonate. The wild-type and mutant strain were distinguished using Random amplified polymorphic DNA PCR and DNA fingerprinting analysis. Plackett-Burman and Box Behnken design were statistical tools used to determine important media parameters and optimization, respectively. Phenotypically and genetically, the new improved strain was different from the wild-type. The most important media parameters from PDB influencing fructosyltransferase production were ammonium chloride, sucrose and yeast extract at  < 0.05. Some significant parameters obtained with the BBD exhibited quadratic effects on FTase. The values (35.37 and 32.11), correlation coefficient (0.98 and 0.97) and the percent coefficient of variation (2.53% and 2.40%) were obtained for extracellular and intracellular FTase respectively. The validation of the model in the improved strain resulted in an overall 6.0 and 2.0-fold increase in extracellular and intracellular FTase respectively compared to the wild-type. A relatively low FTase-producing strain of NAC8 was enhanced for optimum production using a two-pronged approach involving mutagenesis and statistical optimization. The improved mutant strain also had remarkable biotechnological properties that make it a suitable alternative than the wild-type.