POLYHYDROXYBUTYRATE CONTENTS IN CYANOBACTERIUM Synechocystis sp. PCC 6803 WILD TYPE AND adc1 MUTANT

Abstract

In this study, cyanobacterium Synechocystis sp. PCC 6803 wild type (WT) and adc1 gene mutant cells (Δadc1) were used for PHB production under nutrient deficiencies and carbon source supplementation. Moreover, the effect of ultraviolet (UV) stress on PHB production of WT cells were also investigated. Cell cultures of both strains at late-log phase were harvested and transferred to nitrogen and phosphorus deficient BG11 medium (BG11-N-P). Carbon sources including acetate (A) and glucose (G), was also added in BG11-N-P for treated cells, namely BG11-N-P+A and BG11-N-P+G, respectively. Cell growths of WT and Δadc1 under all nutrient modified conditions were significantly decreased when compared with cells grown under normal BG11 condition. For intracellular pigments of both strains were significantly decreased. However, the addition of acetate in BG11-N-P+A significantly enhanced the intracellular pigments compared with those under BG11-N-P condition, whereas glucose addition did not. Furthermore, cell growth and intracellular pigments were obviously decreased by UV exposure, especially UV-C radiation. Additionally, Nile-red stained cells showed widespread accumulation of PHB granules under BG11-N-P+A in both WT and Δadc1. The highest PHB content of WT was quantitatively obtained under BG11-N-P+A condition at 9 day-treatment with the average value of 24.95 ± 18.3 %PHB/DCW whereas Δadc1 gave the highest amount of about 36.07 ± 9.24 %PHB/DCW at 7 day-treatment. Furthermore, WT cells treated by UV-C radiation significantly increased PHB content at 6 hour-treatment of about 13.69 ± 3.09 %PHB/DCW compared with cells treated by normal light. Moreover, genes related to PHB biosynthetic pathway including phaA, phaB, phaE and phaC were determined by RT-PCR. The phaC transcript level was increased by all nutrient modified conditions of both strains compared to those levels of other pha genes. Altogether, the results indicate that the increased PHB content was mainly induced by N- and P-deficient medium containing 0.4% (w/v) acetate condition in WT and adc1 mutant. The UV stress, in particular, UV-C, also enhanced PHB content in WT cells.