| Soil can be considered as a multicomponent,forming an open biochemical system where several physical,chemical and biological reactions may occur.In this system,both matter and energy can also be exchanged with the surroundings,which are composed of a conglomerate of solids,liquids and gases.Soil microorganisms play an essential role in the environment due to their role in many reactions,such as in cycling nutrients,decomposing organic materials, promoting/suppressing plant growth and various soil biophysical processes.Microcalorimetry has been extensively used in recent years,to study the interaction between heavy metals and microorganisms.Being a universal,integral,non-destructive,and highly sensitive tool for a variety of biological investigations,the isothermal microcalorimetric technique can directly measure the biological activity and continuously monitor heat production of a living system,thereby providing both qualitative and quantitative information beyond that obtained from traditional methods.Arsenic is of increasing concern due to its high toxicity and widespread existence in the environment,while polycyclic aromatic hydrocarbons(PAHs) are one class of toxic environmental pollutants that have accumulated in the environment due to a variety of sources.In this paper,a Thermal Activity Monitor-TAMⅢmulti-channel microcalorimetric system was used to monitor the toxic action of inorganic arsenite[As(Ⅲ)]on metabolic activity of Bacillus subtilis and that of pyrene on growth of PAHs-degrading bacteria Acinetobacter junii,respectively.This research consists of two main parts:1.Microcalorimetry and measurement of culture turbidity were applied to evaluate As(Ⅲ) toxic effect on the metabolic growth of B.subtilis.The power-time curves of the matabolic activity of B.subtilis during growth were obtained and studied using a multi-channel thermal activity monitor at different concentrations of As(Ⅲ).The turbidity changes during B.subtilis growth with As(Ⅲ) measured with UV-VIS spectrophotometry agree with the results obtained by microcalorimetry.Low and high concentrations of As(Ⅲ) affect the metabolic growth of B. subtilis in a biphasic dose-response way(hormesis),i.e.stimulation at low-concentration(10μg mL-1) and inhibition at high-concentration(20-160μg mL-1).A typical J-shaped relationship exist between the growth rate constant(k) and c,and the half inhibitory concentration(IC50) was 98.82±7.32μg mL-1.The agreement of the response between the two methods demostrates the validity and sensitivity of microcalorimetric technique to study the toxic effect of As(Ⅲ) on the metabolic growth of soil mircoorganisms.2.A multi-channel thermal activity microcalorimeter was used to study the effect of pyrene on the metabolic activity of PAHs-degrading bacteria A.junii.The power-time curves of microorganism metabolism at different concentrations of pyrene indicate that the bacteria has the potential to degrade pyrene and its capability depends on the concentrations of pyrene in the system.The entire doses of pyrene(50-200μg mL-1) used in this study were able to,to different extent,stimulate the metabolic growth of the tested bacteria.However,the low concentration of pyrene(50μg mL-1) stimulate the growth of A.junii more than higher concentrations of pyrene(100-200μg mL-1),i.e.the stimulation decreased with the increase of the concentrations of pyrene(100-200μg mL-1).The biomass of this bacteria growth obtained was consistent with the results obtained by the microcalorimetric method.The results obtained by the two methods also illustrated microcalorimetric technique is convient and efficient to investigate the action of various concentrations of pyrene on soil microorganisms.
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