This chapter presents a representative choice of examples illustrating the use of continuous culture as a tool for the study of mixed microbial populations. Microorganisms possess a wide variety of mechanisms for structural and functional phenotypic adaptation to their environment. In natural environments, microorganisms often grow in the presence of low concentrations of a diversity of compounds, several of which may make up combinations of homologous substrates, that is, substrates that serve a similar metabolic function, for instance, carbon sources, and nitrogen sources. Chemostat enrichment is probably the best method for selectively isolating microbial communities. The danger with laboratory model systems is undoubtedly that they may be identified with the natural system itself. Many studies have dealt with the responses of bacterial populations, growing in continuous cultures under steady state conditions, to a nutritional shift-up, either by increasing the concentration of the growth-limiting substrate or by increasing dilution rate.

To understand the role played by microorganisms in the formation of cold seep carbonates, we conducted an integrated microbial, mineralogical and organic geochemical study of methane-related authigenic carbonate crusts formed on eastern Mediterranean mud volcanoes. We show that supersaturation with respect to carbonate minerals is induced by microbial anaerobic oxidation of methane. Combined lipid biomarker analysis and 16S rRNA gene surveys identified a highly diversified methane-consuming archaeal community possibly comprising novel species, implying that the anaerobic oxidation of methane is phylogenetically widespread and directly implicating these organisms in the process of crust precipitation. Moreover, pore-water sulphate gradients produced by co-occurring methane-based sulphate reduction exert the main control on aragonite versus magnesian calcite precipitation. We propose that this may be the dominant mode of carbonate crust formation at cold seeps world-wide, in agreement with aquatic chemistry predictions and explaining carbonate mineralogy.

Fresh forage crops such as maize, grasses, legumes, wheatand lucerne can be preserved by ensiling. In many countries ensiledforages are highly valued as animal feed. In European countriessuch as The Netherlands, Germany and Denmark more than 90%of the forages locally produced are stored as silage. Even incountries with generally good weather conditions for hay makingsuch as France and Italy approx. 50% of the forages are ensiled(Wilkinson

In 1590 a Dutch craftsman named Zacharias Janssen who specialized in making spectacles produced the first compound microscope. At first such microscopes had lenses of poor quality and could not be used to see microbial life. By 1630, however, single-lens microscopes came into existence. The oldest records in English referring to microscopic examinations are those of Nathaniel Highmore in 1651, who described his observations on the development of the chicken embryo with the help of “Glasses” and “this Glasse,” probably referring to a compound microscope and a single-lens instrument, respectively (Bardell, 1982).