Study On Microbial Secondary Metabolites

Soluble microbial products (SMP) and extracellular polymeric substances (EPS) are the main matters of microbial secondary metabolites,which are released largely by microorganisms while organic pollutants are utilized in biological wastewater treatment. They are mainly excreted during substrate metabolism process and biomass decay process, and the majority components of them are polysaccharides,proteins,DNA and humic substances,which are affected by the process parameters. Both of them can be biodegraded in some degree,and act as ligands and complex with heavy metals commonly found in wastewaters and sludges.In addition to effect on the effluent,they can also influence the kinetic activity and the flocculating and settling properties of activated sludge microorganisms.Except for these,each other has its own physical state,composition,characteristics and emphasis of study.And there are contradictions about the relationships of SMP and EPS all the times.Upon the former researches,the formation,characteristics of microbial secondary metabolites and the relationships of SMP and EPS are studied.In the experiment of the formation of microbial secondary metabolites excreted by different microorganisms in each decay process,it's found that the formation process of SMP can be divided four main phases:excreting;biodegrading;excreting and autolyzing;biodegrading and autolyzing process, and it's associated with the type of microorganisms,the species contained in the microorganisms and the activity of microorganisms.Through the experiment of biodegradation of SMP by P.putida,it discovers that SMP produced by activated sludge in MBR are biodegradable by other (not their own) microorganisms,and that humic substances and aromatic substances etc,as part compounds of SMP , are readily degraded by P.putida.The molecular weight distribution of SMP exhibited a bimodal style.The degradation ability of the bacteria renews more faster in the higher concentration of original SMP,and SMP inhibits P.putida from respiration more lightly in the lower concentration of original SMP in the whole process.Comparing with the high MW materials(>30kDa),the low MW matters(<1kDa) are more readily degraded,and its inhibition is more lightly to bacteria.In the beginning of the experiment of activated sludge decay process,bound EPS are hydrolyzed to biomass associated products(BAP),and the cell lysis products also constitute part of SMP.In the phase of SMP biodegradation,part of SMP,being biodegradable,are utilized by active biomass as recycled electron donors.At the same time,bound EPS and utilization associated products(UAP) are produced,and there exists cell lysis faintly.Later,the dominating processes are bound EPS hydrolyzing to BAP and bacteria'autolysis.The most products of cell autolysis are adsorbed by bound EPS at first,and then dissolved into the SMP system.And there exists adsorption-desorption between bound EPS and the high MW fractions of SMP.When degraded for some time,the toxicity of SMP enhances,starting to restrain the activity of biomass.While in the presence of toxic materials,more SMP are released by microorganisms.