Abstract
Biohydrogen is a clean and renewable form of hydrogen, which can be produced by photosynthetic bacteria in outdoor large-scale photobioreactors using sunlight. In this study, the transcriptional response of Rhodobacter capsulatus to cold (4 °C) and heat (42 °C) stress was studied using microarrays. Bacteria were grown in 30/2 acetate/glutamate medium at 30 °C for 48 h under continuous illumination. Then, cold and heat stresses were applied for two and six hours. Growth and hydrogen production were impaired under both stress conditions. Microarray chips for R. capsulatus were custom designed by Affymetrix (GeneChip®. TR_RCH2a520699F). The numbers of significantly changed genes were 328 and 293 out of 3685 genes under cold and heat stress, respectively. Our results indicate that temperature stress greatly affects the hydrogen production metabolisms of R. capsulatus. Specifically, the expression of genes that participate in nitrogen metabolism, photosynthesis and the electron transport system were induced by cold stress, while decreased by heat stress. Heat stress also resulted in down regulation of genes related to cell envelope, transporter and binding proteins. Transcriptome analysis and physiological results were consistent with each other. The results presented here may aid clarification of the genetic mechanisms for hydrogen production in purple non-sulfur (PNS) bacteria under temperature stress.
Highlights
The increasing demand for energy leads to search for alternative energy sources
The Gram-negative Purple non-sulfur (PNS) bacterium R. capsulatus has long been studied for its versatile metabolism, nitrogen fixation and hydrogen production
In this study we investigated the effects of temperature stress on hydrogen production metabolism of
Summary
The increasing demand for energy leads to search for alternative energy sources. Hydrogen is a renewable and environmentally safe alternative to fossil fuels, which cause global warming. Özgür et al [7] studied the effect of fluctuating temperatures on hydrogen production of an R. capsulatus hup− mutant in outdoor photobioreactors. They showed a decrease in hydrogen production in daily fluctuations of temperature (15–40 °C) and light/dark cycle. Androga et al [8] investigated the factors affecting hydrogen production of R. capsulatus hup− strain under outdoor conditions and showed the decrease in hydrogen yield during the winter (October–December) in Ankara, Turkey where night temperatures were less than 5 °C. Avcioğlu et al [9] reported that the temperature in the four-liter outdoor photobioreactor could increase above 45 °C, causing decrease of hydrogen productivity and yield. Production metabolism of R. capsulatus were investigated at the transcriptome level and reported here for the first time
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