Soil is an environment that is inhabited by many bacteria including Streptomyces coelicolor.  This bacterium is part of the phylum Actinobacteria, the order Actinomycetales, family Streptomycetaceae and domain Bacteria (12).  It has been found in almost all soil types and is the second most isolated bacteria in soil (11). S. coelicolor is an important part of the carbon cycle and is responsible for the breakdown of biopolymers such as chitin, xylan and cellulose using exoenzymes (9).  Therefore, S. coelicolor is a chemoorganoheterotroph that is active at high pH levels (3).

The bacteria S. coelicolor is non-motile, filamentous, and gram-positive (6).  It is usually not found in wet soils because it is aerobic and is usually out-competed by other unicellular bacteria (11).  It is part of a group of bacteria that contains a high G+C base composition.  For S. coelicolor 70-74% of its genome is G+C base pairings, allowing for it to withstand large changes in temperature, pH and salinity.  This is essential for survival in the ever-changing soil environment (5).  The earthy smell of soil is the result of S. coelicolor and the remaining 500 other species of Streptomyces found in soil (6).

In July 2001 the genome of S. coelicolor was successfully sequenced from 325 overlapping clones.  The fragments were assembled, and the software Artemis was used to annotate the information.  The research was conducted because Streptomyces spp. are responsible for over 6000 different chemical products, including antibiotics, anti-cancer drugs, immunosuppressant, pesticides and other pharmaceuticals.  In addition Streptomyces spp. is used to produce over two-thirds of the naturally derived antibiotics on the market.  A fully sequenced genome would open the door for further discoveries by genetically engineering new sequences that code for new chemical products (1).

Figure 2

S. coelicolor in particular has been found to produce four drugs including, Actinorhodin which is seen in Figure 2 as the blue halo around the bacteria, Undecylprodigiosin is the red pigment in Figure 3, Calcium-dependant antibiotic, and Methylenomycin (8).  In addition, Figure 4 shows the formation of an antibiotic droplet by S. coelicolor.  Furthermore, the production of antibiotics allows for S. coelicolor to be resistant to the bacteriophage phiC31 (7).  S. coelicolor's large genome of 7000 genes is being used against superbugs such as MRSA which causes blood poisoning.  Scientists are confident that S. coelicolor contains the tools necessary to fight back (4).

f
Figure 3

                                                                                       
                                                                                                         Figure 4

Figure 6

The filamentous stucture of S. coelicolor resembles that of fungi and so does its complex life cycle.  S. coelicolor form aerial mycelia which give rise to sporophores after the vegetative growth period.  These sporophores release spores called conidia which are dispersed and form new S. coelicolor bacteria (2).  This life cycle can be seen in Figure 5, and Figure 6 shows the spores of a S. coelicolor.  At this point in time it is speculated that the formation of aerial mycelia may be a result of nutritional limitations (10).

Figure 5

Although Streptomyces spp. are able to survive in the ever changing environment of soil, there are microbes that inhabit the harshest conditions found on earth called extremophiles.  These microorganisms are part of the domain Archaea, which have been found to live in deep sea vents, hot springs, and a variety of other conditions thought to be too harsh to support life.  One of these archaeons called Ferroplasma acidarmanus was isolated from deep inside an old mine shaft.

 Not all microorganisms fall under the domains Bacteria and Archaea.  The third domain of microorganisms is called Eukarya.  Perhaps the best known eukaryotic organism is Saccharomyces cerevisae, which we all know better by its common name yeast.  Of course the most commonly known use of yeast is for the production of beer.  *Click on the keg to learn more about this fascinating eukaryote*. 
 

References