Performance and Mechanism of Protein Production by Photosynthetic Bacteria Utilizing Food Waste: Influence of Light Intensity and Light Cycle.

Photosynthetic bacteria (PSB) are protein-rich and a high-quality producer of microbial proteins. In this study, PSB were cultivated using self-fermented kitchen waste fermentation broth under controlled light intensity and light cycle conditions. Biomass and protein concentrations were measured daily, and microbial community composition and functional succession were analyzed using high-throughput sequencing and bioinformatic tools to investigate the effects of photoperiod on PSB growth and protein synthesis. The results showed that PSB had the highest biomass and protein production of 1356.5 mg/L and 564.3 mg/L at 4000 lx and 24 h light/0 h dark, respectively. Organic pollutant removal was also the highest, with 89.7% chemical oxygen demand (COD) removal and 65.8% ammonia nitrogen removal. Microbiological analysis indicated that the selected light intensity and light/dark cycles were highly favorable for PSB growth. Under these conditions, the dominance of Rhodopseudomonas was further strengthened. During the cultivation process, PSB adjusted its metabolic pathway and shifted its metabolic focus from carbon metabolism to nitrogen metabolism. In addition, the activities of ribulose bisphosphate carboxylase (Rubisco), a key enzyme for photosynthesis, and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and succinate dehydrogenase (SDH), key enzymes of the tricarboxylic acid (TCA) cycle, were enhanced in PSB. These findings provide an important reference for an in-depth understanding of the growth characteristics, metabolic responses, and protein biosynthesis of PSB in the treatment of kitchen waste fermentation broth.