Light-Driven Electron Uptake from Nonfermentative Organic Matter to Expedite Nitrogen Dissimilation by Chemolithotrophic Anammox Consortia

Nonphotosynthetic microorganisms are typically unableto directlyutilize light energy, but light might change the metabolic pathwayof these bacteria indirectly by forming intermediates such as reactiveoxygen species (ROS). This work investigated the role of light onnitrogen conversion by anaerobic ammonium oxidation (anammox) consortia.The results showed that high intensity light (>20000 lx) caused ca. 50% inhibition of anammox activity, and total ROS reached167% at 60,000 lx. Surprisingly, 200 lx light was found to induceunexpected promotion of the nitrogen conversion rate, and ultravioletlight (<420 nm) was identified as the main contributor. Metagenomicand metatranscriptomic analyses revealed that the gene encoding cytochrome c peroxidase was highly expressed only under 200 lx light. N-15 isotope tracing, gene abundance quantification, and externalH(2)O(2) addition experiments showed that photoinducedtrace H2O2 triggered cytochrome c peroxidase expression to take up electrons from extracellular nonfermentativeorganics to synthesize NADH and ATP, thereby expediting nitrogen dissimulationof anammox consortia. External supplying reduced humic acid into alow-intensity light exposure system would result in a maximal 1.7-foldincrease in the nitrogen conversion rate. These interesting findingsmay provide insight into the niche differentiation and widespreadnature of anammox bacteria in natural ecotopes. Ultraviolet light-induced trace H2O2 may trigger another electron transfer chain activity of anammoxconsortia to promote its nitrogen metabolism.

Automated summary

Nonphotosynthetic microorganisms can indirectly utilize light energy to change their metabolic pathways by forming intermediates such as reactive oxygen species (ROS). High intensity light (>20000 lx) inhibits anammox activity, while 200 lx light unexpectedly promotes the nitrogen conversion rate with ultraviolet light (<420 nm) as the main contributor. Photoinduced trace H2O2 triggers cytochrome c peroxidase expression, facilitating electron uptake and nitrogen dissimilation. These findings provide insights into the niche differentiation and widespread nature of anammox bacteria.