Single-phase and two-phase cultivations using different light regimes to improve production of valuable substances in the anoxygenic photosynthetic bacterium Rhodopseudomonas faecalis PA2

This study aimed to improve biomass, carotenoid, bacteriochlorophyll, protein, lipid, and carbohydrate contents of Rhodopseudomonas faecalis PA2 using different light regimes. Light intensity (4000, 6000, 8000, and 10,000 lx), together with photoperiod (24:0, 16:8, 12:12, and 8:16 h light/dark), was assigned as single-phase (SP) cultivation while two-phase (TP) cultivation used two light intensities (using 4000 lx as the first phase), together with the control of phase shift (3, 6, and 9 days) and photoperiod. Biomass, carotenoid, and bacteriochlorophyll contents were maximized by SP cultivation; light at 8000 lx with light-dark cycle of 24:0 was optimal for pigments synthesis. In contrast, TP was useful to enhance storage compounds; protein, lipid, and carbohydrate productivities were significantly increased by 121.69%, 101.69%, and 92.44%, respectively, in TP when compared with SP. This indicates that the novel light strategy proposed in this study was able to manipulate the production of valuable substances in this strain.

The LH2 Complexes (B800-850 and B800-830) Are Assembled in the Cells of the Sulfur Bacterium Thiorhodospira sibirica Strain Kir-3 without Carotenoids

The results of assembling the light-harvesting complexes in the cells of the purple sulfur bacterium Thiorhodospira (T.) sibirica strain Kir-3 while suppressing the biosynthesis of carotenoids with diphenylamine (DPA) were studied. LH2 complexes (B800-850 and B800-830) with different carotenoid composition were isolated from the cells obtained. Maximum inhibition of carotenoid biosynthesis (~90% of the control) was reached at an inhibitor concentration of 53.25 μM (9 mg/L). It was established that changes in the qualitative and quantitative composition of carotenoids do not affect the assembly of B800-830 and B800-850 complexes. It is assumed that, in the population of DPA-LH2 complexes from T. sibirica strain Kir-3, both the carotenoidless complexes and the complexes containing one or two carotenoid molecules can be assembled. These results support the hypothesis that carotenoids are not required for assembling B800-850 and B800-830 complexes.