Effects of Some Environmental Factors on Growth Characteristics of Candida utilis on Peat Hydrolysates

Abstract

Samples of peat from Pine Island and Brookston bogs in Minnesota were hydrolyzed with various concentrations of HCl or H 2 SO 4 solutions, before or after debituminization (an extraction process used to remove waxy materials, bitumens, from peat), to produce peak hydrolysates as growth substrates for Candida utilis. Hydrolysates were neutralized with concentrated NaOH solution to pH 3.5, 4.5, 5.0, 5.5, 6.0, and 7.0. The precipitated humates were removed by filtration. The resulting peat hydrolysates were amended with reagent-grade K 2 HPO 4 , K 2 SO 4 , and MgSO 4 , 200, 100, and 50 mg per liter of peat hydrolysate, respectively. The debituminized peat produced more total nitrogen (TN) and reducing substances (RS) than the nondebituminized peat. Peat hydrolysates produced by HCl solutions contained slightly higher RS and TN than those produced by H 2 SO 4 solutions; however, the latter were better growth substrates than the former. The yield coefficients in both H 2 SO 4 and HCl hydrolysates initially decreased at 12 to 24 h and then increased gradually over the remaining incubation period (24 to 96 h). As TN and RS were increased, an increase in cell density, biomass, and productivity was observed. In contrast, a decrease in specific growth rate occurred as the RS and TN were increased. The generation time of C. utilis was affected by the concentrations of RS and TN. A peak substrate yield coefficient was found at pH 5.0 in HCl hydrolysates and at pH 6.0 to 6.5 in H 2 SO 4 hydrolysates. Good linear correlation coefficients were found between RS and biomass of C. utilis. The coefficients of correlation increased as the TN level in hydrolysates was increased.