Do carotenoids protect phytodetritus-associated bacteria from oxidative stress?

This study focused on how carotenoid pigments in bacteria attached to phytoplankton protect them from singlet oxygen produced by phytoplankton during senescence, specifically under illumination of the diatom Thalassiosira sp. Its effect was analyzed on bacterial membrane structure (photooxidation of bacterial membrane lipids such as mono-unsaturated fatty acids (MUFAs) and on DNA repair system in two bacterial species, non-pigmented Pseudomonas stutzeri and pigmented Dinoroseobacter shibae. In P. stutzeri cells, ¹O₂ transferred from phytodetritus was not completely scavenged by bacterial membranous MUFAs and reached the cytoplasm, allowing both ¹O₂ and UV radiation to cause a rapid response of DNA repair systems. In D. shibae, scavenging by bacterial membrane MUFAs and quenching by spheroidenone allowed only a small fraction of ¹O₂ to reach the cytoplasm, as shown by a delayed and lower repair system activation. The fact that Rhodobacteriales is the dominant order in bacterioplankton communities associated with algal blooms could thus be partly due to the protective effect of its constituent carotenoids against ¹O₂- and UV-induced damage.