Abstract
We isolated a mutant that produced higher levels of curdlan than the wild strain Agrobacterium sp. ATCC 31750 by chemical mutagenesis using N-methyl-N-nitro-nitrosoguanidine. The mutant strain produced 66 g/L of curdlan in 120 h with a yield of (0.88) while, the wild strain produced 41 g/L in 120 h with a yield of (0.62) in a stirred bioreactor. The mutant could not produce curdlan when the pH was shifted from 7.0 to 5.5 after nitrogen depletion as followed for wild strain. In contrast, pH optimum for cell growth and curdlan production for mutant was found to be 7.0. We optimized the downstream processing of curdlan by varying different volumes of NaOH and HCl for extraction and precipitation of curdlan. The molecular weight of the purified curdlan from the wild and mutant strain was 6.6 × 105 Da and 5.8 × 105 Da respectively. The monosaccharide analyses confirm that curdlan from both wild and mutant strain contains only glucose units. From the NMR and FTIR data, it has been confirmed that curdlan was exclusively composed of β (1 → 3)-D-glucan residues.
Highlights
Curdlan is a high molecular weight, water insoluble extracellular polysaccharide composed only of β-(1!3) glucose residues (Lee et al 1999)
Mutant development and curdlan production using shake flask cultures More than 100 mutants were obtained from Agrobacterium sp
Only curdlan producing colonies appeared blue on the aniline blue agar plates and the interaction of the polymer with the dye was proportional to the concentration of the polymer (Nakanishi et al 1976)
Summary
Curdlan is a high molecular weight, water insoluble (alkali soluble) extracellular polysaccharide composed only of β-(1!3) glucose residues (Lee et al 1999). It acts as a structural macromolecule in the cell wall of yeast, mushrooms and other higher plants (Ko and Lin 2004). Curdlan is extensively used as an ingredient in animal feed since it acts as immune stimulator (Lee et al 1999 & Kumari and Sahoo 2006) It is used as concrete admixture and increases the water absorbing capacity of
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