Spectral bands of incandescent lamp leading to variable productivity of purple bacteria biomass and microbial protein: Full is better than segmented

Purple non-sulfur bacteria (PNSB) are competent microorganisms capable of producing value-added products from waste streams. Light source is one of the most influential factors determining the efficiency of this process. Previous studies mostly focused on optimizing light intensity, while the impact of spectral bands on PNSB growth is still un-known. To fill the knowledge gap, this study investigated the responses of PNSB (i.e., Rhodobacter sphaeroides) growth, protein content and enzyme activity to various spectral bands of an incandescent lamp for the first time. It was found that the full spectrum of the incandescent lamp was propitious to cultivate PNSB than segmented spectral bands, as demonstrated by the maximum biomass yield of 1.05 g biomass g(-1) CODremoved, specific growth rate of 0.53 d(-1) and protein concentration of 0.48 g L-1. The production of biomass and protein under infrared (IR) spectral band were slightly lower than those under full spectrum, but 3.2 and 1.7 times higher than the average values (0.14 g L-1 and 0.07 g L-1) under visible spectral bands, respectively. The variation trends of enzymatic activities, such as fructose-1,6-bisphosphatase (FBP) and photopigments were consistent with that of PNSB biomass upon varying spectral bands, suggesting that the spectral bands might induce a variable PNSB biomass via affecting the Calvin cycle and photophosphorylation process. These results provide a new perspective that spectrum bands of light sources should be considered in the process optimization.

Automated summary

This study investigated the impact of various spectral bands of an incandescent lamp on the growth, protein content, and enzyme activity of Purple non-sulfur bacteria (PNSB). It was found that the full spectrum of the incandescent lamp was more favorable for PNSB cultivation compared to segmented spectral bands. Biomass and protein production under the infrared (IR) spectral band were slightly lower than the full spectrum, but significantly higher than the visible spectral bands. Enzymatic activities showed consistent trends with PNSB biomass, suggesting that spectral bands can affect PNSB growth through the Calvin cycle and photophosphorylation process.