Adaptation to Photooxidative Stress: Common and Special Strategies of the Alphaproteobacteria Rhodobacter sphaeroides and Rhodobacter capsulatus

Abstract

Photosynthetic bacteria have to deal with the risk of photooxidative stress that occurs in presence of light and oxygen due to the photosensitizing activity of (bacterio-) chlorophylls. Facultative phototrophs of the genus Rhodobacter adapt the formation of photosynthetic complexes to oxygen and light conditions, but cannot completely avoid this stress if environmental conditions suddenly change. R. capsulatus has a stronger pigmentation and faster switches to phototrophic growth than R. sphaeroides. However, its photooxidative stress response has not been investigated. Here, we compare both species by transcriptomics and proteomics, revealing that proteins involved in oxidation–reduction processes, DNA, and protein damage repair play pivotal roles. These functions are likely universal to many phototrophs. Furthermore, the alternative sigma factors RpoE and RpoHII are induced in both species, even though the genetic localization of the rpoE gene, the RpoE protein itself, and probably its regulon, are different. Despite sharing the same habitats, our findings also suggest individual strategies. The crtIB-tspO operon, encoding proteins for biosynthesis of carotenoid precursors and a regulator of photosynthesis, and cbiX, encoding a putative ferrochelatase, are induced in R. capsulatus. This specific response might support adaptation by maintaining high carotenoid-to-bacteriochlorophyll ratios and preventing the accumulation of porphyrin-derived photosensitizers.

Molecular Profiling and Optimization Studies for Growth and PHB Production Conditions in Rhodobacter sphaeroides

“…ROS are rapidly generated in the cells depending on the levels of light and oxygen, growth stage, and temperature change [26,[42][43][44]. Although ROS mediates adaptative responses to environmental change, high levels of ROS cause oxidative stress such as degradation of proteins and lipid peroxidation [24,25].…”

“…There have also been many reports on oxidative stress signaling in R. sphaeroides. In the microbial cells, oxidative stress is mainly caused by reactive oxygen species (ROS), which are generated from diverse cellular processes and environmental factors such as light, oxygen, and temperature [23][24][25][26]. ROS scavenging mechanisms have been evolutionally developed to combat oxidative stress, which leads to severe cellular damage in R. sphaeroides.…”

Comparative Genome Analysis Provides Molecular Evidence for Reclassification of the Photosynthetic Bacterium Rhodobacter sphaeroides EBL0706 as a Strain of Luteovulum azotoformans

“…The Rhodobacter genus is comprised of heterogenous members showing flexibility in ecophysiology and metabolic capability [ 1 , 2 , 3 ]. Members of the genus can fix atmospheric nitrogen and carry out anoxygenic photosynthesis, thereby allowing them to adapt to various environments and play key roles in global biogeochemical cycles [ 4 , 5 , 6 ].…”

Editorial for the Special Issue: Advances in the Biology of Phototrophic Bacteria

“…This Special Issue highlights recent advances in these aspects. It includes results specifically on green sulfur bacteria (Chlorobi [3]), heliobacteria (Firmicutes [4]), Chloroflexi [5], Cyanobacteria [6,7] and phototrophic purple bacteria (Proteobacteria [8][9][10][11][12][13]). In addition, phylogenetic studies regarding photosynthesis and osmotic adaptation consider representatives of all of these phyla [14,15].…”

“…This Special Issue includes results on identification and genomic characterization of new isolates [9], the adaptation to specific ecological niches in regard to temperature [6], salinity [14] and pH [4]. It also considers aerobic phototrophic purple bacteria and the relations to oxygen and oxidative stress [8][9][10][11]13] as well as environmental interactions [5,7,12] and syntrophic relations [3].…”