Microbial Physiology

 

The Microbial Physiology group 

For more information about microbial physiology or education/graduation projects mail to: fons.stams@wur.nl Some MSc Thesis projects can be found here , for more detailed questions please ask the responsible person mentioned with the project description, Also BSc, MSc minor and Bachelor (Van Hall Larenstein) students are welcome to do a thesis or practical period in the lab of Microbial Physiology.

Introduction

The research carried out by the members of the Microbial Physiology Group focuses on anaerobic bacteria that play an important role in biotechnological processes such as wastewater treatment and soil bioremediation. Senior researchers in the group are Fons Stams, Caroline Plugge and Gosse Schraa.

The research deals mainly with the following subjects:

Microbial production of methane and hydrogen
The use of the sulfur cycle for the removal of metals and S-compounds
Anaerobic oxidation of methane
Bioelectricity
Oxidative and reductive conversions of xenobiotics
Utilization of uncommon electron acceptors by microorganisms

Research is generally carried out in multidisciplinary projects with the Molecular Ecology group, the Bacterial Genetics group and/or the sub-department of Environmental Technology. Graduation research projects can be found here.

Production of methane and hydrogen - Syntrophic interactions

Hydrogen, seen as a promising clean fuel, may ultimately be derived from renewable energy sources. The microbiological production of hydrogen from sugars or via the conversion of CO is studied. Syntrophic interactions play an important role in the formation of methane in anaerobic wastewater treatment systems. Methane is the useful end product, while here hydrogen is an intermediate in the anaerobic degradation process. The concentration of hydrogen (and also formate) has to be extremely low in order to make oxidations of volatile fatty acids (VFAs) such as propionate energetically feasible. Presumably, syntrophic interactions also play an important role in the transformation of several xenobiotic compounds.

The use of the sulfur cycle for the removal of metals and S-compounds

The competition between sulfate-reducing bacteria and methanogenic archaea has been studied previously in different ecosystems, e.g. anaerobic wastewater systems, sediments and pure cultures. However, these interactions are still not completely understood.Biological desulfurisation of hydrocarbon waste streams with sulfate and elemental sulfur as end product is an interesting alternative for physicochemical removal. The possibilities for anaerobic biodegradation of volatile organic sulfur compounds are investigated.Different techniques, e.g., pure culture studies, (mixed population) fermentor studies, and molecular ecological methods, are used to study the interactions between different groups of bacteria.

Example of the sulfur cycle at the Everglades, Terms that are italicized (for example, Diffusion) are processes; bold type indicates interfaces.
 (Public information by the US geological Survey)

Anaerobic oxidation of methane (AOM)

Atmospheric methane (CH₄) is the second most important greenhouse gas after CO₂. Anaerobic oxidation of methane (AOM) plays a major role in the sub-seafloor methane flux and in marine sediments. The main sources for methane production in ocean sediments are thermogenic methane formation and microbial methane formation in past and present. Also methane hydrates at the seafloor are releasing methane to the seawater and consequently to the atmosphere. Methane can be degraded by means of microbial oxidation under both aerobic and anaerobic conditions. Current research revealed that methane diffusing upwards from deep sites of sediments often disappears before any contact with oxygen is possible and microorganisms are thought to consume methane in such anoxic zones. The amount of methane consumed by anaerobic methane oxidation each year is approximately equivalent to 5 to 20% of the total annual methane flux to the atmosphere. However, the microorganisms responsible for this process have not yet been isolated. Only quite recently, it was found that the process might be catalyzed by a consortium of organisms. In our laboratory we carry out research to get detailed insight into bacterial AOM at both moderate and high temperature conditions. Isolation efforts are performed under different conditions like micro-aerophillic and high pressure (100 bar). highly enriched sludge in a membrane bioreactor is used for developing molecular tools for detecting these very slow growing organisms.

Bioelectricity

In microbial fuel cells (MFCs) microorganisms conserve chemical energy as electricity. In these microbial fuel cells microorganisms use inert electrodes as terminal electron acceptor for growth on organic compounds. By using molecular biological techniques we study which microorganisms are active at the cathode and the anode sides of the MFC. Also, we aim to get insight into the molecular mechanism of exocellular electron transfer. Several organic electron mediating compounds like quinones and riboflavin, have been described that can mediate exocellular electron transfer. Recently, research carried out in the US has suggested that redox proteins organized in so-called conductive nanowires may be involved in exocellular electron transfer. In microbial fuels cells electricity may also be used to drive reactions that are energetically difficult. One of these conversions is the electricity-mediated electrolysis of organic acids for the production of hydrogen.

Oxidative and reductive conversions of xenobiotics
(chlorinated hydrocarbons and aromatic compounds)
 

 


Utilization of uncommon electron acceptors by microorganisms

Some microorganisms use oxidized metal(loid(s)) or chlorate as electron acceptor.

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