Promoting Photosynthetic Bacterial Pigment Production in Chloroflexus aurantiacus Y-400-fl via Enhanced Biological Sulfide Removal: Exploring Light Intensity Effects and Carbon Sources

This study investigates the potential of an extremophile green non-sulfur bacterium (GNSB), Chloroflexus aurantiacus strain Y-400-fl, for producing value-added products, including photosynthetic pigments (total carotenoids and bacteriochlorophylls (BChls)) and biopolymers (polyhydroxyalkanoates, PHAs), while biologically removing sulfide (S 2– ) in a single-stage process at 50 ºC. The impact of varying volumetric light intensities (from 0.8 to 3.9 W L –1 ) was evaluated and C. aurantiacus could accumulate BChl c , total carotenoids, and PHAs of up to 2.9, 2.2, and 1.9% dcw, respectively, at ~3.6 W L –1 while maintaining effective S 2– removal at initial concentration of ~10 mg S 2– L –1 . Glycyl-glycine supplementation enhanced BChl c accumulation and biomass production. Conversely, increasing volumetric light intensity, as a stress condition, had a detrimental effect on PHA accumulation. A robustness test revealed that S 2– concentrations up to 109 mg L –1 , within realistic ranges of industrial emissions, did not inhibit the growth of GNSB or the accumulation of pigments. Therefore, C. aurantiacus can efficiently remove S 2– while simultaneously synthesizing pigments at 50 ºC, thus reducing the cost associated with photobioreactors’ cooling and sterilization. This opens the possibility of developing new and sustainable bioprocesses for simultaneous desulfurization and pigment production.