Streptomyces coelicolor colonies with aerial mycelium and spores. The area of the picture represents about 2x3 cm. The blue haloes around the colonies are secreted actinorhodin. Actinorhodin is an antibiotic (not used clinically) which is blue under alkaline conditions and red under acidic conditions. Actinorhodin is a polyketide made by multiple condensations of acetate by a Type II polyketide synthase (John Innes Centre, Photography Department).