A bacteriophytochrome regulates the synthesis of LH4 complexesin Rhodopseudomonas palustris

Abstract

The non-sulphur purple bacterium Rhodopseudomonas palustris contains five pucAB genes for peripheral light-harvesting complexes. Bacteria grown under high-light conditions absorb at 800 and 850 nm but in low-light the 850 nm peak is almost absent and LH2 complexes are replaced by LH4. The genome contains six bacteriophytochromes (Bph). Bphs sense light in the red/far-red through a reversible Pr to Pfr transformation that controls gene expression. Bph3 (RPA1537) controls the expression of a cluster of photosynthetic genes, however most of the peripheral light harvesting complex genes are outside of this region. The pucAB-d genes encode LH4 peptides and are near two Bphs (RPA3015, RPA3016). We have characterised three Bphs and show that Bph4 RPA3015 and Bph3 RPA1537 have different dark stable states. It is known that Bph3 is active in its red absorbing Pr form and suggests a working hypothesis that Bph4 is active in the Pfr state. We show that LH4 expression can be induced with red light at the Pr absorption maximum (708 nm) of Bph4. The property of light transmission of water maybe an important factor in understanding this adaptation. Bph4 can sense the reduction in light intensity indirectly through an increase in ratio of transmitted red/far-red light. The red right activated Bph4 regulates the synthesis of LH4 which concentrates bacteriochlorophyll a pigment absorption at 800 nm to exploit a recovery in water light transmission in this region.

Abundance and Diversity of the Phototrophic Microbial Mat Communities of Sulphur Mountain Banff Springs and Their Significance to the Endangered Snail, <i>Physella johnsoni</i>

“…palustris; Figure 2(M)) isolated from both PS agar deeps and PMS-containing Balch tubes. On PMS plates, these strains anaerobically produce large amounts of Bchl relative to carotenoids (ratio 1:1.7) where, as previously observed by Evans et al [45], the photosynthetic RC was the dominant complex with Bchl a peak maxima near 808 nm at absorbance values over four times those of the LHI peak at 878 nm (Figure 4(J)). The LHII peak appeared as a subtle shoulder to the left of LHI near 860 nm.…”

Apo-bacteriophytochromes modulate bacterial photosynthesis in response to low light

“…We created in-frame deletion mutants of RpBphP2 or RpBphP3 and assayed LH4 expression in cells by measuring the ratio of whole-cell absorbance at 800 nm to absorbance at 860 nm. The LH4 complex predominates when this ratio is >1, and the LH2 complex predominates when the ratio is <1 (16,19). We found that deletion of either one of the RpBphP genes disrupted LH4 synthesis in response to low light intensity, similar to previous reports (7,8) (Fig.…”

“…An increase in LH4 synthesis is seen in R. palustris cells grown in red light under semiaerobic conditions (7,16). This finding is consistent with the conclusion that under semiaerobic conditions, BV is synthesized and incorporated into RpBphPs, allowing them to respond to red light.…”

“…This finding is consistent with the conclusion that under semiaerobic conditions, BV is synthesized and incorporated into RpBphPs, allowing them to respond to red light. R. palustris also increases the synthesis of its LH4 complexes in response to a decrease in white light intensity when grown anaerobically, and both RpBphP2 and RpBphP3 are required for this response (7,8,16). In plants and cyanobacteria, phytochromes have been implicated in the sensing of light intensity, for which their ability to bind a chromophore and carry out photoconversion is essential (17,18).…”

Tracking energy transfer between light harvesting complex 2 and 1 in photosynthetic membranes grown under high and low illumination

“…In the PSU, LH2 complexes surround the LH1/RC complexes in a two-dimensional network, the size and composition of which is controlled by a range of environmental conditions, including oxygen tension, incident light intensity, and light quality (8)(9)(10). In the case of the most studied purple photosynthetic bacterium Rhodobacter sphaeroides, the LH complexes and RCs are only synthesized when the oxygen tension is below a critical value (11,12).…”