Mixed culture cultivations Natural

In many cases, microbial life in nature develops into zones within which communities are dominated by one or a few functional groups, such as aerobes, sulfate reducers, or methanogens. Distinct zoning is characteristic, for example, of microbial mats (Konhauser, 2007), hot springs (Fouke et al., 2003), marine sediments and freshwater muds (Berner, 1980), contaminated aquifers (Bekins et al., 1999), and pristine groundwater flows (Chapelle and Lovley, 1992). Communities develop as well in laboratory experiments, when microbes are cultivated in pure or mixed culture. 

Doujiang is fermented by naturally occurring or cultivated microorganisms (Kim, Lee, et al., 2010), including Bacillus amyloliquefaciens. Bacillus megaterium, Lactobacillus fermentum and Lactobacillus plantarum, and yeasts such as Candida humilis, Kluyveromyces lactis, Williopsis satumus and Z. rouxii. In industry the natural fermentation can be simulated by using a mixed starter of Z. rouxii and L. plantarum these starter cultures obviously do not fully represent the microbial community in the traditional production (Zhao et al., 2009). 

Several bioreactor designs are used to produce bioproducts, and include, but are not limited to batch reactors, fed-batch reactors, continuous cultivation reactors, plug flow reactors, recycle bioreactor systems, immobilized cell reactors, biofilm reactors, packed bed reactors, fluidized-bed reactors, and dialysis cultivation reactors (Williams 2002). These reactor types can contain either mixed or pure cultures, and can stimulate heterotrophic and/or phototrophic cellular functions depending on the specific reactor design. Additionally, these reactor schemes can be used to produce products directly, or to harvest biomass or other products for downstream processes. Due to the complex nature of bioreactors, particularly anaerobic digesters, the use of metagenomics is helpful to understand the physiology of such systems. 

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