The role of the core microorganisms in the microbial interactions in activated sludge

In order to gain a deeper understanding of the microbial interactions in wastewater treatment plants (WWTPs) in China and clarify the role of the core community in the microbial interactions in activated sludge (AS), this study used a molecular ecological network approach based on random matrix theory to construct co-occurrence networks of the core microorganisms (CoreN), the whole AS community (WholeN) and the microbial communities without the core microorganisms (OtherN), respectively. It was shown that the WholeN had more complex and tighter connections compared with the OtherN, because of its higher total number of nodes, higher average clustering coefficient, and shorter average geodesic distance. The proportions of positive links in the CoreN, WholeN and OtherN were gradually decreased, indicating that the core microorganisms promoted cooperation between AS microorganisms. Moreover, higher robustness after random removal of 50% of the nodes of the WholeN (0.2836 & PLUSMN; 0.0311) was observed than the robustness of the OtherN (0.1152 & PLUSMN; 0.0263). In addition, the vulnerability of OtherN (0.0514) is significantly higher than WholeN (0.0225). Meanwhile, the average ratio of negative/positive cohesion, was significantly decreased when the core microorganisms were removed. These results demonstrated that core community could strengthen the stability of the ecological network in AS. By discerning the key factors affecting ecological network, AS temperature was observed to have a strong correlation with all three networks. Moreover, pollutants in wastewater shown stronger correlations with the CoreN and WholeN, supporting the point that core community play a critical role in pollutant removal in WWTPs to a certain extent.

Automated summary

In this study, a molecular ecological network approach was used to construct co-occurrence networks of core microorganisms (CoreN), whole activated sludge community (WholeN), and microbial communities without core microorganisms (OtherN) in wastewater treatment plants in China. The results showed that WholeN had more complex and tighter connections compared to OtherN. The core microorganisms promoted cooperation between AS microorganisms. Moreover, WholeN exhibited higher robustness and lower vulnerability compared to OtherN. These results demonstrate the importance of the core community in enhancing the stability of the ecological network in activated sludge.