Puf operon sequences and inferred structures of light-harvesting complexes of three closely related Chromatiaceae exhibiting different absorption characteristics

Whole cells of the purple sulfur bacterium strain 970 exhibit an unusual absorption peak at 963 nm. Its closest relatives, Thiorhodovibrio (Trv.) winogradskyi DSM6702(T) and strain 06511 display a bacteriochlorophyll (BChl) a absorption peak at 867 nm that is characteristic for most light-harvesting complexes 1 (LHC1) of proteobacteria. The puf operons encoding the LHC1 and reaction center proteins were amplified, cloned, and sequenced, and for the Trv. winogradskyi, strains show the common pufBALMC gene arrangement, whereas strain 970 contains a second pufBA copy downstream of pufC. Only pufB(1)A(1) is transcribed, and the corresponding mRNA fragment had an increased stability. Alignments of the deduced protein sequences showed that the LHC1 polypeptides are closely related to those of Thermochromatium (Tch.) tepidum. A deletion between αHis(0) and αTrp(+11), thought to be responsible for the redshifted Q(y) absorption in Tch. tepidum, was also detected in strain 970 and Trv. winogradskyi, whereas αLys(+12) is replaced by histidine only in strain 970. Based on our structural modeling, the side chain of this αHis is predicted to be in close proximity to the BChl a, suggesting that it exerts a modulating effect on the spectral properties of the highly unusual LHC1 complex of strain 970.