Impact of Phosphate, Potassium, Yeast Extract, and Trace Metals on Chitosan and Metabolite Production by Mucor indicus

Abstract

In this study the effects of phosphate, potassium, yeast extract, and trace metals on the growth of Mucor indicus and chitosan, chitin, and metabolite production by the fungus were investigated. Maximum yield of chitosan (0.32 g/g cell wall) was obtained in a phosphate-free medium. Reversely, cell growth and ethanol formation by the fungus were positively affected in the presence of phosphate. In a phosphate-free medium, the highest chitosan content (0.42 g/g cell wall) and cell growth (0.66 g/g sugar) were obtained at 2.5 g/L of KOH. Potassium concentration had no significant effect on ethanol and glycerol yields. The presence of trace metals significantly increased the chitosan yield at an optimal phosphate and potassium concentration (0.50 g/g cell wall). By contrast, production of ethanol by the fungus was negatively affected (0.33 g/g sugars). A remarkable increase in chitin and decrease in chitosan were observed in the absence of yeast extract and concentrations lower than 2 g/L. The maximum chitosan yield of 51% cell wall was obtained at 5 g/L of yeast extract when the medium contained no phosphate, 2.5 g/L KOH, and 1 mL/L trace metal solution.

Keywords: Mucor indicus; chitosan; ethanol; phosphate; potassium; trace metals; yeast extract.

Figure 1

Effect of different phosphate concentration on glucosamine (GlcN) yield (g/g alkali-insoluble material (AIM)) (black bars) and N-acetyl glucosamine (GlcNAc) yield (g/g AIM) (white bars). Error bars represent the ± standard deviation (SD) of values obtained from independent experiments performed in triplicate. Average SD: p = 0.00 (black bars); p < 0.02 (white bars).

Figure 2

Effect of different potassium hydroxide concentrations on GlcN yield (g/g AIM) (black bars) and GlcNAc yield (g/g AIM) (white bars). Error bars represent the ± standard deviation (SD) of values obtained from independent experiments performed in triplicate. Average SD: p <0.02.

Figure 3

Effect of trace metals at different levels of KOH (without H₃PO₄) on GlcN (g/g AIM) (black bars) and GlcNAc yields (g/g AIM) (white bars): (a) cultures without trace metals; (b) cultures including trace metals. Error bars represent the ± standard deviation (SD) of values obtained from independent experiments performed in triplicate. Average SD: p < 0.015.

Figure 4

Effect of different concentrations of yeast extract on GlcN yield (g/g AIM) (black bars) and GlcNAc yield (white bars) (g/g AIM). Error bars represent the ± standard deviation (SD) of values obtained from independent experiments performed in triplicate. Average SD: p <0.03 (black bars); p <0.015 (white bars).