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This study has thoroughly uncovered the characteristics of the marine euphotic zone system in the Beibu Gulf, featuring adjacent semiconducting minerals and electrochemically active microbes, via mineralogical characterization, photoelectrochemical measurements, and microbiological analysis techniques. Notably, results of Raman and ESEM with EDS indicated that anatase, the semiconducting mineral with prominent photocatalytic performance, exists in large quantities in the Beibu Gulf. Photoelectrochemical measurements tested photoelectric response and redox activity of suspended particulate minerals, demonstrating the suspended particulates dominated by titanium and iron oxide semiconducting minerals presented excellent photo-response property and distinct photoelectric catalytic potential under visible light irradiation. Its significant property of photoelectric response with 110.483% increment ratio of the average photocurrent density relative to the dark current density. 16S amplicon sequence analysis revealed that the euphotic zone was dominated by Proteobacteria, Actinobacteria, and Cyanobacteria at the phylum level, and by Synechococcus CC9902, Cyanobium PCC-6307 and unclassified Ilumatobacteraceae at the genus level. Halomonas (0.2–1.2%), Vibrio (0.7–1.8%), and Nautella (0.1–1.1%), closely related to semiconducting minerals reduction reaction, were also presented in YL and RGS samples of the Beibu Gulf. This work firstly revealed that the neglected characteristics of the marine euphotic zone system in the Beibu Gulf of the South China Sea, which is an important natural ecosystem for microorganisms to uptake energy sources. It will provide a new perspective for further research on novel ways for microorganisms to acquire energy sources through semiconducting minerals in the marine euphotic zone system. [ABSTRACT FROM AUTHOR]

Dolomite exhibits a wide distribution in geological strata. The metabolic activities of microorganisms in marine sediments play a crucial role in the formation of dolomite. Semiconducting minerals, such as hematite, goethite, and rutile, generate photoelectrons when exposed to sunlight, which can impact the community structure and metabolic activities of microorganisms. In this study, a simulated photoelectron system was conducted to investigate the response of the microbial community, as well as the regulation of sulfate reduction, to photoelectrons using high-throughput sequencing of the 16S rRNA gene. The regulatory effect of semiconducting mineral photoelectrons on the induction of carbonate precipitation by sulfate-reducing bacteria was explored. X-ray diffraction and Raman spectroscopy were used to characterize carbonate precipitation. During cultivation, the pH values of the system increased from 8.0 to approximately 8.5 and the rate of sulfate reduction was significantly enhanced under the influence of simulated photoelectrons. The alpha diversity of the microbial community decreased, and the semiconducting mineral photoelectronic system had a promoting effect on the enrichment of sulfate-reducing bacteria, mainly Desulfovibrio. Under the regulation of photoelectrons, sulfate-reducing bacteria can effectively oxidize organic matter and reduce sulfate in the environment, and proto-dolomite can be formed at a low Mg/Ca ratio. This process has important implications for carbon and sulfur element cycling in estuarine and oceanic photic zones, and provides a new explanation for the formation of large amounts of dolomite in geological history. [ABSTRACT FROM AUTHOR]