International Journal of Marine Science, 2025, Vol.15, No.4, 209-219 http://www.aquapublisher.com/index.php/ijms 209 Feature Review Open Access Symbiotic and Antagonistic Relationships between Microalgae and Environmental Microorganisms Weihong Liu, Qikun Hang Tropical Microbial Resources Research Center, Cuixi Academy of Biotechnology, Zhuji, 311800, Zhejiang, China Corresponding author: qikun.huang@cuixi.org International Journal of Marine Science, 2025, Vol.15, No.4, doi: 10.5376/ijms.2025.15.0019 Received: 11 Jul., 2025 Accepted: 16 Aug., 2025 Published: 27 Aug., 2025 Copyright © 2025 Liu and Hang, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Liu W.H., and Hang Q.K., 2025, Symbiotic and antagonistic relationships between microalgae and environmental microorganisms, International Journal of Marine Science, 15(4): 209-219 (doi: 10.5376/ijms.2025.15.0019) Abstract There is a complex interaction between microalgae and environmental microorganisms, including two major categories: mutually beneficial symbiosis and hostile antagonism. This interaction not only affects the functions of aquatic ecosystems, but also has great significance for applications such as biomass energy production and sewage treatment. This study outlines the biological characteristics of microalgae and the diversity of environmental microbial communities, elaborates on the symbiotic mechanisms of nutrient complementarity, matter exchange, signaling, etc. of microalgae-microbial interaction, as well as hostile effects such as nutritional competition, allelosensitivity inhibition, viral parasitism and predation. Typical cases such as symbiosis between cyanobacteria and nitrogen-fixing bacteria, co-culture of microalgae-heterotrophic bacteria to improve biofuel yield, and disintegration of algae blooms by viruses, revealing the far-reaching impact of microalgae-microbial interaction on community diversity, water bloom succession and global carbon, nitrogen and phosphorus cycle. On this basis, we look forward to the future research directions in molecular mechanism analysis, multiomics technology application and ecological engineering regulation. Keywords Microalgae; Environmental microorganisms; Symbiosis; Antagonism; Algae interaction 1 Introduction Microalgae are a type of tiny algae that can perform photosynthesis. They are widely distributed in the ocean, freshwater and wetland environments. Their photosynthetic carbon sequestration occupies an important position in the global primary productivity. In nature, a large number of microorganisms such as bacteria, fungi, viruses, and protozoa are found around microalgae, which together constitute the so-called "algaein circle" microenvironment (Zhou et al., 2014; Kuhlisch et al., 2023). The interaction relationship between these microalgae and environmental microorganisms can be roughly divided into two aspects: mutually beneficial symbiotic relationship and mutually inhibited hostile relationship. The symbiotic relationship between microalgae and microorganisms is of great significance to maintaining the function and balance of aquatic ecosystems. On the one hand, microalgae fix CO2 through photosynthesis and release oxygen and organic carbon sources to provide energy and nutrients to heterotrophic microorganisms; on the other hand, bacteria and other microorganisms feed back to microalgae by decomposing organic matter, regenerating nutrients or synthesizing vitamins to promote the growth of algae. This symbiosis mechanism of nutritional complementarity not only improves the community's utilization efficiency of resources, but also shows application value in the fields of sewage treatment, bioenergy, etc. (Morris et al., 2022). At the same time, there are also hostile effects such as competition and antagonism between microalgae and microorganisms. Eutrophication of water bodies often leads to overpropagation of certain microalgae to form "water blooms", which leads to changes in bacterial community structure and nutrient competition. Some bacteria secrete algal soluble substances to inhibit algae growth, while viral infection can lead to lysis of algae cells and accelerate algae bloom decay (Lin et al., 2024). These hostile effects not only affect algae population dynamics, but also may cause ecosystem dysfunction, such as water bloom disintegration, resulting in deterioration of water quality and a decrease in biodiversity.
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