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Gerard H Markx

Publications and source records attributed to Gerard H Markx.

7 recordsLinked to original sources
PubMed2005

Construction of artificially structured microbial consortia (ASMC) using dielectrophoresis: examining bacterial interactions via metabolic intermediates within environmental biofilms.

The construction of artificial biofilms with defined internal architectures is described. Bacterial cells are suspended in a low conductivity medium, guided to specific areas in a microelectrode array by dielectrophoresis (DEP), and then immobilised using the flocculating agent poly(ethylenimine). Multispecies biofilms can be constructed by introducing different species at different times. The rapid construction of such biofilms with defined internal architectures provides, when combined with visual reporters of gene activity, a powerful new method for the investigation of the effects of the spatial organisation on interactions between bacterial species in biofilms. To demonstrate the utility of the technique as a method for investigating metabolic interactions in biofilms, aggregates were constructed from Acinetobacter sp. C6 and Pseudomonas putida::gfp. The Acinetobacter degrades benzyl alcohol, overproducing benzoate, which in turn is consumed by the Pseudomonas strain. The P. putida has a chromosomally expressed cassette encoding a gfp downstream of the promoter which controls degradation of benzoate, making the interaction between the two strains in the metabolism of benzyl alcohol visible by the production of green fluorescent protein (GFP). Microscopic observation of the biofilms, including the use of confocal laser scanning microscopy (CLSM), confirmed that metabolic exchange occurred. In addition, it was observed that the bacteria appear to have a preferred biofilm architecture, with P. putida in the bottom layer, and Acinetobacter at the top.

Acinetobacter↗
PubMed2005

Colonial architecture in mixed species assemblages affects AHL mediated gene expression.

Many bacterial species produce metabolites that accumulate in the extracellular environment and induce specific transcriptional responses in producing cells. This phenomenon, most often referred to as quorum sensing, is thought to constitute a self-cell-density sensing mechanism allowing bacterial populations to alter gene expression in response to increases in their own density. Quorum sensing systems involving N-acyl-L-homoserine lactone (AHL) production and response are the most intensively investigated example. In this study we have employed a novel technique, known as dielectrophoresis, to investigate the impact of colonial architecture on the induction of AHL mediated gene expression. Using dielectrophoresis, we constructed artificial mixed species microcolonies with specific architectures. In this way, we were able to show that approximately 1000 Escherichia coli cells layered over an immobilised cluster of approximately 500 AHL responsive cells alters the response of this cluster to AHLs supplied either exogenously or endogenously. These findings lend credence to the hypothesis that the accumulation of extracellular metabolites signifies generic crowding in mixed species assemblages.

4-Butyrolactone↗
PubMed2004

Towards microbial tissue engineering?

Tissue engineering involves the creation of multicellular tissues from individual cells. It was previously perceived that tissues were only formed by higher organisms such as plants and animals. However, it is now known that multicellular systems of microorganisms, such as microbial colonies, biofilms, flocs and aggregates, can also show extensive spatial organization. Here, we discuss methods that can be used to spatially organize microorganisms--bacteria, in particular--into tissue-like materials with defined internal architectures. Some potential uses of such "microbial tissues" are covered.

Animals↗
PubMed2003

Construction of biofilms with defined internal architecture using dielectrophoresis and flocculation.

A novel approach was developed for the construction of biofilms with defined internal architecture using AC electrokinetics and flocculation. Artificial structured microbial consortia (ASMC) consisting of localized layered microcolonies of different cell types were formed by sequentially attracting different cell types to high field regions near microelectrodes using dielectrophoresis. Stabilization of the microbial consortia on the electrode surface was achieved by crosslinking the cells using the flocculant polyethyleneimine (PEI). Consortia of Escherichia coli, Micrococcus luteus, and Saccharomyces cerevisiae were made as model systems. Also, more natural consortia were made of the bacteria Pseudomonas putida, Clavibacter michiganense, and Methylobacterium mesophilum, which are found together in consortia during biodegradation of metal-cutting waste fluids.

Actinomycetales↗
PubMed2002

Electro-orientation of Schizosaccharomyces pombe in high conductivity media.

The orientation of microbial cells may be important in cell-cell interactions within microbial consortia. As part of our research programme aimed at the construction of Artificial Structured Microbial Consortia (ASMC), we have investigated the electro-orientation of Schizosaccharomyces pombe in AC electric fields, and studied the effects of the applied frequency, voltage, and distance between the electrodes, at different medium conductivities. It is shown that the electro-orientation of S. pombe in media with conductivities similar to that of growth media is feasible using microelectrodes. Oriented growth of S. pombe can be obtained when continuously exposed to AC electric fields in growth medium over extended periods.

Culture Media↗
PubMed2002

A simple method for the measurement of bacterial particle conductivities.

A method was developed for the measurement of the bacterial particle conductivity, based on the measurement of the conductivity of a bacterial cell suspension sigma(s) and the suspending medium sigma(m). A line plotted through sigma(s) - sigma(m) versus sigma(m) crosses the x-axis at sigma(m) = sigma(p), independent of the bacterial cell concentration. The method does not require anything more complex than a centrifuge and a conductivity meter. Knowledge of the bacterial particle conductivity is of importance in, for example, the dielectrophoretic separation, manipulation and trapping of bacterial cells, as well as the study of their physiological state.

Bacteria↗