Cellulose-1-4-β- cellobiosidase activity in soils
Abstract
Soil management practices such as crop rotation, tillage, organic matter input, and cover crops can greatly affect physical, chemical, and biological properties that affect soil microbial communities and extracellular enzyme activities through the alteration in soil organic carbon. There is an increasing demand for large scale biomass production, making the relationship between crop production and soil health more important. For sustainable healthy soils, the extracellular enzymes are of great importance because they play vital role in nutrient cycling through the ecomposition of carbon compounds of plant cell wall and cellulose is the most abundant carbon molecule in the plant cell wall. As the most abundant biopolymer on earth, cellulose is broken down by an array of enzymes that have varied specificities and act in synergism. An assay protocol was developed to detect and quantify activity of a cellulose degrading enzyme, cellulose 1,4-β-cellobiosidase (EC 3.2.1.91) in soil. In addition to developing an assay method to quantify activities of cellobiosidase in soil, series of experiments were conducted to determine the effect of pH, storage temperature and time, and trace elements on stability and activity of cellobiosidase in soil. Moreover, the relationships among several cellulosic and carbon-transforming enzymes, and between their activities and microbial biomass and activities in soil cultivatedwith switchgrass. Data shown that the optimum β-cellobiosidase activity in soil were approximately pH 5.5 and 60°C, respectively. The Michaelis constants (Km) and maximum
velocity (Vmax) in the tested six soils ranged from 0.08 to 0.51 mM for Km and from 71.5 to 318.1 µmol kg soil-1h-1for Vmax. The temperature coefficient (Q10) ranged from 1.72 to 1.99, and the activation energy (Ea) ranged from 42.5 to 53.7 kJ mol-1. Soil pH, sample storage temperature and time, trace elements, and management practice affected stability and/or activity of cellobiosidase in soil. The tested enzyme activities had mostly positively correlated each other and with microbial biomass carbon content, with the exception of urease activities which was negatively correlated with microbial biomass. Enzyme activities were not significantly correlated with microbial respiration, suggesting that the detected activities are mostly originated from cell-free enzymes that have been stabilized by soil.
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- OSU Dissertations [11222]