Biohydrogen obtained from purple non sulfur bacteria (PNSB) is an environmentally friendly alternative for hydrogen production. PNSB can be employed in large scale outdoor photobioreactors to produce hydrogen by photofermentation with sunlight as the light source. In external environmental conditions, however, bacteria can experience stress due to high light intensities, which can inhibit or slow down hydrogen production. Previous studies with other PNSB showed varying responses to light intensities (above 4000 lux), in some cases improving, and in others adversely affecting hydrogen production.

In this study, Rhodobacter capsulatus, a PNSB species that produce hydrogen efficiently from dark fermenter effluents containing acetate, was used to investigate the effects of high light intensity stress on the hydrogen production metabolism at the gene expression level. A microarray analysis was carried out using a custom-design Affymetrix GeneChip TR_RCH2a520699F. R. capsulatus DSM1710 was grown under a cyclic illumination of 2000 and 7000 lux (12 h light/12 h dark) in a hydrogen production medium having 30 mM acetate and 2 mM glutamate, and was exposed to a high light intensity (10,000 lux) for 1 h in the middle of a light period. The results reveal that photosynthetic reaction center genes were down-regulated in order to protect the photosynthetic membrane from damage. On the other hand, the expression of nitrogenase and electron transport system genes were enhanced by high light intensity. These results show that a high light intensity stress drives R. capsulatus to direct gene expression towards hydrogen production, which supports the hypothesis that hydrogen production is a way for the disposal of excess reducing equivalents to maintain the internal redox balance.

从紫色非硫细菌（PNSB）获得的生物氢是生产氢气的环保替代品。PNSB可用于大型室外光生物反应器中，以太阳光为光源通过光发酵产生氢。但是，在外部环境条件下，细菌可能会由于高强度的光照而受到压力，从而抑制或减缓氢气的产生。先前与其他PNSB的研究表明，对光强度（4000勒克斯以上）的响应有所不同，在某些情况下有所改善，而在另一些情况下则对制氢产生不利影响。

在这项研究中，使用荚膜红细菌（一种从含乙酸盐的深色发酵液中有效产生氢的PNSB物种）在基因表达水平上研究高光强度胁迫对氢产生代谢的影响。使用定制设计的Affymetrix GeneChip TR_RCH2a520699F进行了微阵列分析。荚膜红球菌DSM1710在2000和7000 lux（12 h亮/ 12 h暗）的循环光照下在具有30 mM乙酸盐和2 mM谷氨酸的制氢介质中生长，并暴露于高光强度（10,000 lux）下1 h在一个光明的时期。结果表明，光合反应中心基因被下调，以保护光合膜不受损害。另一方面，高光照强度增强了固氮酶和电子传输系统基因的表达。这些结果表明，高的光强度胁迫驱使荚膜红球菌将基因表达引导至产氢，这支持以下假设：产氢是处置过量还原当量以维持内部氧化还原平衡的一种方式。