The Effects And Mechanism Of Surfactants On The Extracellular Enzymes Of Microorganisms During Composting Process

Composting is considered as a useful process for the disposal of municipal and agricultural solid waste. During the composting, the raw material is transformed through a variety of biological and biochemical processes in which enzymes play an important role. Enzymes that catalyze the degradation of biomacromolecules, such as starch, protein, cellulose, hemicellulose and lignin, are extracellular enzymes since the biomacromolecules are too large to be transported across the cellular membrane. Therefore, it is obvious that the enhancement of the extracellular enzyme activities will promote the degradation of the biomacromolecules, which will in turn speed up the composting process.In the present study, a biosurfactant rhamnolipid and a soft chemical surfactant Tween 80 were added into the composting process. The composting experiment, solid state fermentation, endogenetic fluorescence of enzymes and fluorescence probe were used to investigate the effects and mechanism of the two surfactants on the extracellular enzymes from the microorganism during the composting process.During the composting of waste rich in cellulose content, both rhamnolipid and Tween 80 had the increasing and stabilizing effects on CMCase and xylanase activities to different extents, and accordingly speeded up the decomposition of cellulose and hemicellulose. Therefore, the water soluble carbon (WSC) contents, mainly containing glucose and xylose released from the decomposition of cellulose and hemicellulose, in the treatments with surfactants were higher than that in the control during the whole composting process, which partially contributed to the lager microbial community populations than the control. The comparison between the effects of Tween 80 and rhamnolipid on enzyme activities, WSC contents and decomposition of substrate indicated that rhamnolipid is a little superior to Tween 80 during the composting process. The present study revealed that soft surfactants, such as rhamnolipid and Tween 80, might be used in the composting of waste rich in cellulose in order to speed up the composting process.The effect of surfactants Tweeen 80 and rhamnolipid on extracellular enzymes of fungi Penicillium simplicissimum, actinomycetes Streptomyces badius, bacteria Pseudomonas aeruginosa and Bacillus subtilis were related to the types of surfactants, kinds of microorganisms and classification of enzymes. In the whole, Tween 80 is a stimulatory agent for most of the microorganisms and enzymes, while the stimulatory effects of rhamnolipid is confined to a smaller range but it has a prominent effect on some specific enzymes, such as xylanase. Neither Tween 80 nor rhamnolipid had a prohibitory effect on the growth of microorganism.The stability of enzymes varied with pH values. Cellulase was the most stable between pH 3 and 7 and almost did not lose its activity, while xylanase was the most stable between pH 7 and 9 and the activity decreased slowly. The activity cut-down of enzymes due to adsorption by the substrate straw varied with enzymes and pH values. The adsorption of cellulase on straw increased with pH value going higher, while pH value did not have an obvious effect on the adsorption of xylanase. Both Tween 80 and rhamnolipid decreased the adsorption of enzymes on straw and stabilized the activities of cellulase and xylanase.The stabilities of amylase, protease, cellulase and xylanse in different pH conditions were investigated by endogenetic fluorescence of enzymes. Tween 80 and rhamnolipd increased the stability of amylase, cellulase and xylanase to different extends and widened the pH range in which the enzymes kept their molecule structure, but did not have an obvious effect on protease.The actions between surfactants, Tween 80 and rhamnolipid, and four enzymes, amylase, protease, cellulase and xylanase, were studied by fluorescence probe pyrene. The action between rhamnolipid and xylanase was the most strong, with cellulase taking a second place, but the action between rhamnolipid and amylase and protease was not distinct. The actions between Tween 80 and cellulase and xylanase made them combining together well, but amylase and protease went against the micelle formation of Tween 80. Compared with rhamnolipid, the action force between Tween 80 and enzymes was on the small side, but with the increasing of concentration, the action force increased, especially the concentration going over the critical micelle concentration.In conclusion, surfactants Tween 80 and rhamnolipid promoted and stabilized the extracellular enzymes of microorganism in the composting process, which accelerate the degradation of organic matter and improved the composting efficiency, on the other hand, the promoting and stabiling effects were related to type of surfactants, kind of microorganisms, classification of enzymes, pH values and the substrate. In addition, biosurfactant, with the advantage of diversity, being produced in situ and non-toxicity, has a perspective in composting of solid waste.