International Journal of Marine Science, 2025, Vol.15, No.6, 313-319 http://www.aquapublisher.com/index.php/ijms 135 sulfate aerosols in the atmosphere, thereby affecting cloud formation and even potentially fine-tuning the climate (Jackson and Gabric, 2022). But not all DMS can escape from the sea surface - most of them have actually been "eaten" by other microorganisms long ago or disintegrated in the sunlight. Therefore, the actual release of DMS in the ocean largely depends on this delicate balance between transformation and consumption. This balance is controlled by factors such as temperature, light and changes in microbial populations. Moreover, it is very likely to be reshuffled by climate change (Qian et al., 2024). 6 Case Studies: Microbial Contributions to Elemental Cycles in Specific Marine Regions 6.1 Community structure and functions of sulfur-oxidizing bacteria in the black sea anoxic zone The Black Sea, a large oxygen-deficient sea area without seasonal improvement, has long attracted the attention of researchers for its unique features. Near its chemical stratosphere, there lives a type of sulfur-oxidizing bacteria (SOB) that rely on an anaerobic environment. Among them, the most common ones are the SUP05 branch of γ - Proteobacteria, as well as thiomonas and Microspira vulcanis (Vliet et al., 2020). They do not rely on oxygen but use nitrates or manganese oxides to oxidize sulfides. These microorganisms not only participate in carbon fixation, but also support a part of the main productivity at the bottom of the Black Sea - contributing up to nearly half of the primary production (Henkel et al., 2022). The microbial community in the Black Sea is not uniform but rather layered: SOAs are mainly concentrated in the transitional zone of the REDOX cascade, forming complex interactions with the surrounding sulfate-reducing bacteria, methane-oxidizing bacteria and denitrifying bacteria, jointly promoting the cycle among sulfur, carbon and nitrogen. 6.2 Microbial nitrogen cycling characteristics in the pacific thermocline layer The thermocline of the Pacific Ocean serves as a dividing line, where oxygen and nutrients show significant differences between the upper and lower layers, and this precisely provides their respective positions for various nitrogen cycle microorganisms. Archaea like Thaumarchaeota dominate the upper layer of ammonia oxidation, while Nitrospinae are the "experts" in the downstream treatment of nitrite. Further down, in the area where oxygen is nearly depleted, anaerobic ammonia-oxidizing bacteria such as Scalindua and denitrifying bacteria come into play (Pajares and Ramos, 2019). Metagenomic data show that water depth almost determines who stays - the frequent occurrence of certain genes among different populations suggests possible functional redundancy, but ecological selection remains obvious (Figure 2) (Song et al., 2022). The balance between nitrogen supply and loss is quietly achieved among these microorganisms and also affects the primary productivity of the entire sea area. 6.3 Empirical study of carbon uptake by photosynthetic plankton in polar oceans The polar regions are not deserts for life. On the contrary, small photosynthetic phytoplankton thrive there quite vividly. Their ability to absorb carbon largely depends on light, nutrient concentration and ice coverage. In some insitu experiments in the Arctic and subarctic, researchers, using isotope labeling and fluorescence assays, found that these small phytoplankton sometimes contribute more than 80% of total carbon and nitrogen fixation. However, the efficiency of carbon fixation fluctuates greatly in different years and even under different ice conditions. For instance, microphytoplankton and micro-phytoplankton take turns to "take the center stage", which is closely related to light conditions, nitrate consumption rate and phytoplankton size (Zhu et al., 2019). In other words, whether polar phytoplankton communities can adapt to global warming may depend on whether they can flexibly respond to these constantly changing factors. 7 Application of Advanced Techniques in Marine Microbial Research 7.1 Use of metagenomics and metatranscriptomics in functional analysis In the context where many Marine microorganisms cannot yet be cultivated, metagenomic and metatranscriptomic technologies have become shortcuts to directly understand them without culturating them. Researchers have used these techniques to reconstruct the transcriptome of Marine plankton eukaryotes. Some key metabolic processes, such as DMSP synthesis or nitrogen fixation, have thus identified the core "behind-the-scenes players" (Xu et al., 2024). In deep-sea hydrothermal environments, some species, although having similar functions, clearly divide their roles through metabolic differences. Such niche division and collaboration mechanisms have gradually emerged in
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