Microarray analysis of the effects of light intensity on hydrogen production metabolism of rhodobacter capsulatus

Gürgan Eser, Muazzez
Biohydrogen generated by purple non-sulfur bacteria is a clean and renewable method of hydrogen production. It can be achieved in outdoor phototobioreactors using the natural sun light in lab to pilot scales. Light is one of the most important parameter affecting hydrogen production in the outdoor condition. Hydrogen productivity may decrease upon light intensity stress by sun light and the diurnal cycle in outdoor conditions. It is important to understand the metabolic response of these bacteria to varying light and dark periods and high light intensity. For this purpose, the transcriptome of Rhodobacter capsulatus was studied using microarray chips. The experiments were carried out with the wild type R. capsulatus (DSM1710) and an uptake hydrogenase deficient mutant of Rhodobacter capsulatus (YO3) on 30/2 acetate/glutamate medium at 30°C with cyclic illumination of 12h light/12h dark periods. Hydrogen production experiments were performed under 2000 lux and 7000 lux, separately. The bacterial growth, pH, hydrogen production, bacteriochlorophyll a and organic acid profiles were followed by taking samples at the end of each light and dark periods. Bacterial growth ceased and even decreased in the dark and recovered in the light. Concurrently, hydrogen production stopped in dark periods but resumed when light was available and enhanced by 7000 lux light intensity. High light intensity enhanced molar yield (25.5% and 34% for wild type and 37.6% and 51.4% for mutant bacteria under low and high light intensities, respectively). Moreover, molar productivities were significantly enhanced (0.26 and 0.61 mmol/(Lc.h) for wild type and 0.75 and 1.44 mmol/(Lc.h) for mutant bacteria under low and high light intensities, respectively). High light intensity also accelerated substrate consumption. In order to understand the metabolic response of R. capsulatus, microarray analyses were completed for the conditions of shift to light after a dark period, and exposure of bacteria to a stress causing high light intensity (10,000 lux). The results revealed that a shift to light after a dark period stimulated expressions of photosynthetic apparatus, nitrogenase system and electron transport system genes. Transcription processes were intense in darkness, which triggered stress response. High light intensity further enhanced expression of nitrogenase and electron transport system genes to dissipate excess electrons for redox balance, while down-regulated the photosystem genes in order to protect the photosynthetic membrane from damage.  


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Citation Formats
M. Gürgan Eser, “Microarray analysis of the effects of light intensity on hydrogen production metabolism of rhodobacter capsulatus,” Ph.D. - Doctoral Program, Middle East Technical University, 2017.