Evrimsel mühendislik yöntemi ile elde edilen kobalta dirençli Rhodobacter sphaeroides bakterisinin fizyolojik analizi

Rhodobacter sphaeroides is a gram negative purple non-sulfur α-proteobacterium found in soil, mud, deep lakes and stagnate waters. It has metabolic diversity, as it is able to grow under photoheterotrophic, photoautotrophic, chemoheterotrophic and chemoautotrophic conditions. It can alter its metabolism according to the changing environmental conditions and nutrient deficiency. Due to its metabolic versality, sequenced genome and no requirement of unusual conditions for growth, it is commonly used in biotechnological applications. R. sphaeroides is capable of synthesizing and storing biodegradable and biocompatibile polyester polyhydroxybutyrate (PHB) as insoluble inclusion bodies in cytoplasm. Some of the other byproducts of R.sphaeroides in industry are 5-aminolevulinic acid, Coenzyme Q10, carotenoids, vitamin B12, indole terpenoids and plant hormones. Large scale H2 production in a photobioreactor, ZnS nanoparticle production for medical purposes and potential usage in bioremediation are also reasons for biotechnological importance of R. sphaeroides. R. sphaeroides has the ability to survive under changing stress conditions by modifying its cellular and genetic composition. For instance, oxidative stress causes down-regulation of the carotenoid genes, while heavy metal stress increases membrane integrity. In another study, cobalt-resistant R. sphaeroides population was obtained under gradually increasing cobalt stress conditions, using evolutionary engineering approach. The last (64th) population was able to survive 15 mM cobalt stress, with a survival rate of 21%. The last population was spread onto solid Luria Broth plate and eight colonies (called G1-G8) were selected from there. In this study, the selected individual mutants were phenotypically characterized.