Microbial Products

Understanding into how the organic products microogranisms make are critical to microbial activities and communities

Environmental biotechnologists usually focus on the microorganisms’ primary metabolism:  oxidation of electron donors (such as BOD and NH4+) and reduction of electron acceptors (such as NO3- to N2 gas and CO2 to CH4 or acetate).  At the same time, all microorganisms also release organic products that affect water quality and microbial ecology in profound ways.  These are called microbial products, and they fall into two general classes.  The first class, called extracellular polymeric substances or EPS, is solid material that the microorganisms excrete for a range of purposes:  attaching them to surfaces as biofilms; aggregating them into suspended flocs or granules protecting them from predation, toxicants, and desiccation; and allowing conductivity for extracellular electron transport.  The second class is called soluble microbial products or SMP.  Some SMP is created by the hydrolysis of EPS, while other SMP is released directly by the microorganisms in parallel with their primary metabolism.  

Swette Center researchers are active in many facets of understanding EPS and SMP.  The research begins with chemical and microscopic characterization of EPS produced by different types of microorganisms.  In parallel, SMP is characterized for its chemical features and biodegradability.  Center modeling always includes SMP and EPS, as it has profound impacts on the flow of electrons and carbon in the microbial communities and effluent quality.  Special attention is given to how the formation of SMP by autotrophic microorganisms provides organic electron donor for heterotrophic bacteria, which often constitute a major fraction of the biomass in systems that receive only inorganic substrates.  Likewise, the generation and distribution of EPS in biofilms affects biofilm-community structure and function. 

Scanning electron microscopy shows copious EPS in an MXC biofilm

Output of a multi-species model of an MBfR biofilm active in nitrate and perchlorate reductions. EPS are almost equal to the perchlorate-reducing bacteria (PRB), and heterotrophic bacteria (B) are significant even though the only electron donor added is H2 gas, since the H2-oxidizing autotrophs provide SMP to support the HB.