Effect of blue light on growth and exopolysaccharides production in phototrophic Rhodobacter sp. BT18 isolated from brackish water.

Rhodobacter sp. BT18, a phototrophic salt-resistant bacterium, was isolated from brackish water and screened for the production of exopolysaccharides (EPS). The effect of different light sources on the growth of Rhodobacter sp. BT18 was investigated. The effect on the growth order was found to be blue > white > green > red > yellow > dark. Based on Box-Behnken design, the studied variables (pH 7.0, 35 °C, and 30% of sucrose concentration under 60 h of incubation with blue light illumination) were found to be ideal for the maximum production of EPS (582.5 mg/L). Scanning electron microscopy images revealed the porous nature of EPS. Fourier transform spectroscopy and X-ray diffraction were applied to study the functional groups and the crystalline nature of the EPS, respectively. The emulsification index of the EPS was >75% and the maximum flocculating activity was about 75.4% at 30 mg/L concentration of EPS. In addition, EPS showed effective arsenic (64%) and lead (51%) chelating activities in liquid solutions. The multiple environmental applications of the EPS produced by Rhodobacter sp. BT18 make it be a promising alternative for emulsification, flocculation and metal removal in various industries.

Selective repression of light harvesting complex 2 formation in Rhodobacter azotoformans by light under semiaerobic conditions.

Photosystem formation in anaerobic anoxygenic phototrophic bacteria (APB) is repressed by oxygen but is de-repressed when oxygen tension decreases. Under semiaerobic conditions, the synthesis of photopigments and pigment protein complexes in Rhodobacter (Rba.) sphaeroides are repressed by light. AppA, a blue-light receptor, mediates this regulation. In the present study, it was showed that the synthesis of bacteriochlorophyll, carotenoid, and pigment protein complexes in Rba. azotoformans 134K20 was significantly repressed by oxygen. Oxygen exposure also led to a conversion of spheroidene to spheroidenone. In semiaerobically growing cells, light irradiation resulted in a decrease in the formation of photosystem, and blue light was found to be the most effective light source. Blue light reduced the contents of bacteriochlorophyll and carotenoid slightly, but had negligible effects on light harvesting complex (LH) 1 content, whereas the content of LH2 was significantly decreased indicating that blue light selectively repressed the synthesis of LH2 in semiaerobically growing 134K20. It was concluded that, similar to Rba. sphaeroides, a blue light receptor presented in strain 134K20 played important roles in its light-dependent repression. A possible mechanism involved in controlling the differential inhibitory of blue light on the synthesis of photosystem was discussed.

Prospective technology on bioethanol production from photofermentation.

The most important global demand is the energy supply from alternative source. Ethanol may be considered an environmental friendly fuel that has been produced by feedstock. The production of ethanol by microalgae represent a process with reduced environmental impact with efficient CO2 fixation and requiring less arable land. This work studied the production of ethanol from green alga Chlamydomonas reinhardtii through the cellular metabolism in a light/dark cycle at 25 °C in a TAP medium with sulfur depletion. The parameters evaluated were inoculum concentration and the medium supplementation with mixotrophic carbon sources. The combination of C.reinhardtii and Rhodobacter capsulatus through a hybrid or co-culture systems was also investigated as well. C.reinhardtii maintained in TAP-S produced 19.25±4.16 g/L (ethanol). In addition, in a hybrid system, with medium initially supplemented with milk whey permeated and the algal effluent used by R. capsulatus, the ethanol production achieved 19.94±2.67 g/L.

[Regulation mechanism of photopigments biosynthesis via light and oxygen in Rhodobacter azotoformans 134K20].

OBJECTIVE: To provided a reliable and sensitive method and a series of specific absorption spectra data of different carotenoids and bacteriochlorophylla in anxoygenic phototrophic bacteria, and reveal mechanism of regulation of photosynthetic pigments by light and oxygen in Rhodobacter azotoformans 134K20. METHODS: The metabolic diversity of photopigments regulated by oxygen and light was investigated by means of UV-VIS spectra and thin layer chromatography. RESULTS: The highest cell yield of strain 134K20 was obtained under aerobic conditions in the light. Nine types of photopigments including three yellow pigments, one red pigment, one purple pigment, two green pigments, and two blue pigments were synthesized, and yellow pigments synthetic genes were expressed on the higher level anaerobically in the light. Under aerobic conditions, the synthetic genes of two new red and one new purple pigment were triggered and expressed on the higher level, but the biosynthesis of yellow, blue and green pigments were inhibited by oxygen, another nine pigments including two yellow pigments, three red pigments, two purple pigments, one green pigment, and one blue pigment were synthesized. One yellow pigment was only produced in dark aerobic culture, the other pigments were the same as in dark aerobic cultures. CONCLUSION: PpsR photopigment suppression regulation system regulated expression of photosynthetic genes via light and oxygen in Rhodobacter azotoformans 134K20. The yellow and red pigments belong to carotenoid series. The first yellow pigment belongs to spheroidene series. The other two yellow pigments are new carotenoids. Yellow pigments are capable of dissolving in different organic solvents. Red pigments belong to new spheroidenone series. The three red pigments are different in polarity, peak shape and peak value. Fine structures of red pigments only are appeared in hexane. The purple pigmments with polarity are identified as bacteriopheophytins. The blue and green pigments are four kinds of bacteriochlorophyll a intermediates. Diethylether and methanol is suitable for carotenoids extraction. The identification of bacteriochlorophyll a intermediates can be easily performed by polarity analysis.

Tributyl phosphate degradation by Rhodopseudomonas palustris and other photosynthetic bacteria.

Tributyl phosphate (TBP) is widely used in nuclear fuel processing and other waste generating chemical industries. Although TBP is bacteriostatic, some microbes are resistant to it and may degrade it. Under dark aerobiosis, purple non-sulfur photosynthetic bacteria degraded up to 0.6 mM TBP, initially present at 2 mM, within 3 weeks and under photosynthetic conditions, Rhodopseudomonas palustris degraded 1.6 mM TBP within 3 weeks. The curing of the Rhodopseudomonas palustris endogenous plasmid demonstrated that the genes involved in the TBP degradation are chromosomal.

The light-harvesting complex II (B800-850) of Rhodobacter sulfidophilus: characterization and formation under different growth conditions.

The photosynthetic bacterium Rhodobacter sulfidophilus is able to grow chemotrophically and phototrophically at a broad range of light intensities. In contrast to other facultative phototrophs, R. sulfidophilus synthesizes reaction center and light-harvesting (LH) complexes, B870 (LHI) and B800-850 (LHII) even under full aerobic conditions in the dark. The content of bacteriochlorophyll (BChl) varied from 3.8 micrograms Bchl per mg cell protein when grown at high light intensity (20,000 lux) to 60 micrograms Bchl per mg cell protein when grown at low light intensities (6 lux). After a shift from high light to low light conditions, the size of the photosynthetic unit increased by a factor of 4. Chromatographic analysis of the LHII complex, isolated and purified from cells grown phototrophically (at high and low light intensities) and chemotrophically, could resolve only one type of alpha and one type of beta polypeptide in the purified complex, of which the N-terminal sequences have been determined.