Two Distinct crt Gene Clusters for Two Different Functional Classes of Carotenoid in Bradyrhizobium

Abstract

Aerobic photosynthetic bacteria possess the unusual characteristic of producing different classes of carotenoids. In this study, we demonstrate the presence of two distinct crt gene clusters involved in the synthesis of spirilloxanthin and canthaxanthin in a Bradyrhizobium strain. Each cluster contains the genes crtE, crtB, and crtI leading to the common precursor lycopene. We show that spirilloxanthin is associated with the photosynthetic complexes, while canthaxanthin protects the bacteria from oxidative stress. Only the spirilloxanthin crt genes are regulated by light via the control of a bacteriophytochrome. Despite this difference in regulation, the biosyntheses of both carotenoids are strongly interconnected at the level of the common precursors. Phylogenetic analysis suggests that the canthaxanthin crt gene cluster has been acquired by a lateral gene transfer. This acquisition may constitute a major selective advantage for this class of bacteria, which photosynthesize only under conditions where harmful reactive oxygen species are generated.

Isorenieratene Biosynthesis in Green Sulfur Bacteria Requires the Cooperative Actions of Two Carotenoid Cyclases

“…However, this level of enzymatic complexity is reminiscent of the complexity seen in converting phytoene to lycopene. Although a single enzyme, CrtI, can perform the same suite of reactions (22,25,34,46,50), two desaturases and at least one isomerase are required to convert phytoene into lycopene in GSB and most cyanobacteria (1,3,4,6,7,19,21,34,40,43).…”

Complete Biosynthetic Pathway of the C50Carotenoid Bacterioruberin from Lycopene in the Extremely Halophilic Archaeon Haloarcula japonica

“…We reached that conclusion because, in a Bradyrhizobium strain, two distinct crt gene clusters are involved in the synthesis of its carotenoids (spirilloxanthin and canthaxanthin). Each cluster contains the genes crtE (GGPP synthase), crtB, and crtI, leading to the common precursor lycopene (39). In addition, the main products of the ⌬c0507 strain, TH-BABR and DH-IDR, lacked the double bonds at C-3,4 and C-3=,4=.…”

“…2A), and RT-PCR analysis revealed that those genes were cotranscribed. Since carotenoid synthesis-related genes in some bacteria are assembled in clusters or in neighborhoods (34,39), these genes were predicted to be involved in the carotenoid synthesis of Ha. japonica.…”

Evolution of cyanobacterial and plant phytochromes

“…Molecular studies and database searches identified also quite a number of phytochrome-like proteins, which contain one or several GAF domains and various signaltransmitting domains or domains with unknown function [4][5][6][7][8][9]. Bacterial phytochromes and phytochrome-like proteins control diverse effects, such as chromatic adaptation [4], carotinoid synthesis [10,11], chlorophyll synthesis [12], circadian rhythm [6] or phototaxis [7]. Because the first prokaryotic phytochromes and phytochrome-like proteins were discovered in cyanobacteria [4,5,[13][14][15], it was proposed that phytochrome evolution began in this group of prokaryotes [16,17].…”