Adopting a Bacterial Pigment

“Streptomyces coelicolor, a filamentous, high G-C, gram-positive bacteria, was first dubbed Streptothrix coelicolor in 1908 by R. Muller after he found it on a potato. It later became known as Streptomyces coelicolor. They also live in colonies and have structural similarities to fungus. Colonies of Streptomyces coelicolor release pigments that are blue/green in alkali and red in acidic conditions, thereby giving the bacterial colonies those colors under the respective conditions.”

“Streptomycetes are gram-positive, mycelium-forming, soil bacteria that play an important role in mineralization processes in nature and are abundant producers of secondary metabolites. Since the discovery of the ability of these microorganisms to produce clinically useful antibiotics, they have received tremendous scientific attention.”

The blue pigment produced by Streptomyces coelicolor 100 with a yield as high as 3 g/l is a mixture of 10 components. The structure of one of the components was identified and it is a new actinorhodin analogue, named as λ-actinorhodin. The natural pigment can be dissolved in alkaline water solution and a number of organic solvents in common use. The color of a water solution of the pigment changes with pH value. The pigment is stable to light, heat and food additives in common use, and resistant to oxidants and reducers under acidic conditions and to reducers under alkaline conditions. Most inspected metal ions hardly affected pigment stability except for Fe2+ at high concentration and Pb2+. The pigment is nontoxic with LD50 > 15,000 mg/kg in an acute toxicity trial. The good characteristics of the pigment make it potential useful in the food processing industry as an additive.

The properties of the blue pigment produced by Streptomyces sp.ZLT were studied.The results showed that the blue pigment was water-soluble.It was relatively stable at a high temperature.The blue pigment had good resistance against oxidation-reduction at low pH.There was no effect on the blue pigment by most metal ions tested.The blue pigment resisted sunlight under natural conditions and UV ray under alkaline conditions.

Streptomyces coelicolor, a filamentous, high G-C, gram-positive bacteria, was first dubbed Streptothrix coelicolor in 1908 by R. Muller after he found it on a potato(2). Later, it became known as Streptomyces coelicolor. The Streptomyces coelicolor
A3(2) strain studied in depth by David A Hopwood and sequenced by the John Innes Center and the Sanger Institute is actually taxonomically a member of the Streptomyces violaceoruber genus, although it retains the former name, and is not the same strain as the Muller strain(25). Streptomyces coelicolor, like the streptomyces genus in general, live in the soil. Streptomyces are responsible for much of the break down of organic material in the soil as well as the “earthy” smell of soil. They also live in colonies and have structural similarities to fungus. Colonies of Streptomyces coelicolor release pigments that are blue/green in alkali and red in acidic conditions, thereby giving the bacterial colonies those colors under the respective conditions. Other differentiating characteristics of Muller's Streptomyces coelicolor are grayish-yellow aerial mycelium, smooth spores, aerial mycelium lacking spirals, and no melanoid pigment(5). Since the A3(2) strain is actually Streptomyces violaceoruber, it looks a bit different. One distinction is that the A3(2) strain has ash gray aerial mycelium with spirals(5). From this point on, I will refer to Streptomyces coelicolor as the A3(2) strain and not Muller's strain because the A3(2) strain was sequenced, and a great deal of information is available about it. Streptomyces coelicolor are important bacteria and were sequenced because of their “adaptability to environmental stress”, “source of bioactive molecules for medicine and industry”, and “relat[ion] to human pathogens”(3). Streptomyces coelicolor has a very similar core genome to Mycobacterium tuberculosis and Corynebacterium diphtheriae, as well as some similarity to Mycobacterium leprae, so it can be used to study these disease causing bacteria(4). The Streptomyces genus is responsible for producing a majority of the antibiotics in use today, as well as some immunosuppressants and anti-tumor agents. Streptomyces coelicolor also has an interesting life-cycle that includes differentiation into aerial mycelium and spore formation(3).

Scientists have isolated a blue pigment from cultured soil bacteria
that could offer a natural colouring with an excellent stability
and toxicology profile for food.

We recently described a new method to activate antibiotic production in bacteria by introducing a mutation conferring resistance to a drug such as streptomycin, rifampin, paromomycin, or gentamicin. This method, however, enhanced antibiotic production by only up to an order of magnitude. Working with Streptomyces coelicolor A3(2), we established a method for the dramatic activation of antibiotic production by the sequential introduction of multiple drug resistance mutations. Septuple and octuple mutants, C7 and C8, thus obtained by screening for resistance to seven or eight drugs, produced huge amounts (1.63 g/liter) of the polyketide antibiotic actinorhodin, 180-fold higher than the level produced by the wild type. This dramatic overproduction was due to the acquisition of mutant ribosomes, with aberrant protein and ppGpp synthesis activity, as demonstrated by in vitro protein synthesis assays and by the abolition of antibiotic overproduction with relA disruption. This new approach, called “ribosome engineering,” requires less time, cost, and labor than other methods and may be widely utilized for bacterial strain improvement.