No abstract

Arthrospira platensis is one of the most beneficial cyanobacteria due to its high protein content and highvalue compounds such as poly-3-hydroxybutyrate (PHB) and carotenoids which can be used in promoting health in many sectors. A. platensis cultivation can be performed using urban or industrial wastewater as a source of nutrients, including glycerol and phosphorus. The objective of this study was to enhance biomass, pigments, and partial PHB in A. platensis IFRPD1182 grown under different glycerol and phosphorus concentrations. The highest values of biomass, carotenoids, and PHB production were observed in cells grown in the G 3 P 3 medium supplemented with 4.6 g/l glycerol and 356 mg/l phosphorus on the fifth day of cultivation with maximal values of 1.90 ± 0.03 mg/ml, 6.30 ± 0.12 mg/l, and 34.76 ± 2.71 mg/l, respectively. In addition, RT-PCR analysis revealed that the cells grown in G 3 P 3 medium increased crtB and crtP transcripts, encoding phytoene synthase and phytoene desaturase, respectively, and involved in carotenoid biosynthesis with 1.47-and 1.50-fold increases, respectively. This indicates that the increased expression of crtB and crtP genes in the cells can be achieved by a combination of glycerol and phosphorus, where the carotenoids were highly accumulated.

Polyhydroxybutyrate (PHB) is a biocompatible and biodegradable polymer that has the potential to replace fossil-derived polymers. The enzymes involved in the biosynthesis of PHB are β-ketothiolase (PhaA), acetoacetyl-CoA reductase (PhaB), and PHA synthase (PhaC). PhaC in Arthrospira platensis is the key enzyme for PHB production. In this study, the recombinant E. cloni ®10G cells harboring A. platensis phaC (rPhaCAp) was constructed. The overexpressed and purified rPhaCAp with a predicted molecular mass of 69 kDa exhibited Vmax, Km, and kcat values of 24.5 ± 2 μmol/min/mg, 31.3 ± 2 µM and 412.7 ± 2 1/s, respectively. The catalytically active rPhaCAp was a homodimer. The three-dimensional structural model for the asymmetric PhaCAp homodimer was constructed based on Chromobacterium sp. USM2 PhaC (PhaCCs). The obtained model of PhaCAp revealed that the overall fold of one monomer was in the closed, catalytically inactive conformation whereas the other monomer was in the catalytically active, open conformation. In the active conformation, the catalytic triad residues (Cys151-Asp310-His339) were involved in the binding of substrate 3HB-CoA and the CAP domain of PhaCAp involved in the dimerization.