Microbial diversity

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The diversity of a microbial consortium can vary and change with environmental factors (operating parameters) like for example temperature, ammonium concentration and CO2 concentration. Different types of microbes can sometimes perform different functions and sometimes complement each other.

Bacteria are the most diverse and abundant group of organisms on Earth. Attempts to describe bacterial diversity and abundance often yield impressive numbers. For example, there are reports that there is one billion times more individual bacteria on earth than stars in the universe, that the number of prokaryotic species exceeds that of all other species, that prokaryotic cells comprise the majority of all biomass, and that even the most hostile habitats are inhabited by bacteria.

Before the introduction of phylogenetic information by Carl Woese in 1987, microbiologists used morphological and physiological properties to differentiate between bacterial species (see: [http://home.earthlink.net/~douglaspage/id30.html A Tale of Woese). This led to the description of for example Pseudomonas (from Greek: pseudes: false and monas: unit) which in fact comprised at least five different groups of bacteria. However, the advances of molecular methods, despite their limitations and biases, have led to an increased understanding of bacterial diversity. Today there exist numerous molecular tools, for example 16S rRNA clone libraries ,followed by Temperature - or Denaturation Gradient Gel Electrophoresis (DGGE), Fluorescence In Situ Hybridization (FISH), and Quantitative Dot Blot Hybridization. The use of molecular tools led to a rapidly increasing number of publications (see Figure).


Image:record_count.jpg

Record count for "microbial diversity" using ISI Web of Knowledge, March 2008.


Nevertheless, methodological constraints hinder the ability to measure biodiversity, for example the widely used community fingerprinting techniques detect only app. 10% of the most common bacterial species that coexist in freshwater habitats. Furthermore, a consistent bacterial species concept, following the principles of polyphasic taxonomy, which comprises phenotypic, genotypic, and phylogenetic information, is still under consideration. However, the most commonly used bacterial species definition reads as follows: “a category that circumscribes a (preferably) genomically coherent group of individual isolates/strains sharing a high degree of similarity in (many) independent features, comparatively tested under highly standardized conditions”. Estimates of bacterial diversity diverge significantly. For example, a rather low number (1,117) was calculated based on the number of new sequences in GenBank [1] to calculate the number of marine bacterial species found in the ocean. On the other hand, scientists found 1,800 species alone in samples from the Sargasso Sea.

Bioleaching and microbial diversity

Leaching is more effective in mixed communities with certain team-members. Therefore microbe cultures used in bioleaching are usually not pure but have some diversity.

See also

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