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Cylindrospermopsis raciborskii- dominated harmful algae blooms have been reported globally in recent years. However, our understanding of the ecology of C. raciborskii in natural conditions is still poor. In this study, we collected the water samples from a C. raciborskii -blooming lake, Yilong Lake, in Yunnan province, China, and used both culture-dependent and culture-independent approaches to investigate their microbial communities and the interactions between C. raciborskii and the other bacteria. The composition and diversity of microbial communities were revealed with 16S rRNA gene high-throughput sequencing data analysis. Microbial co-occurrences analysis suggests C. raciborskii may have complex associations with other bacteria. Based on co-inoculation tests, we obtained 14 strains of bacterial strains from the water samples that exhibited either algicidal or promoting effects on a strain of C. raciborskii. Two bacterial isolates exhibited a consistent performance between co-occurrence analysis and experimental results. Effects of these bacteria-algae interspecies interactions on the bloom event are discussed. All these results may provide new insights into the C. raciborskii -dominated blooms and how its interspecies relationships with other bacteria may influence the bloom events in eutrophic waters throughout the world. [ABSTRACT FROM AUTHOR]

• The PSR indicator system for Yunnan's ecological security (ES) was developed. • Yunnan's ES had an overall improvement during 2000–2020. • Yunnan's ES had risen at a slower rate than other southwest provinces since 2011. • Scientific theoretical guidance was for Yunnan's ES sustainable development. Yunnan Province is part of the Yun-Gun Plateau in southwest China with rich ecological resources and special geographic features, resulting in considerable ecological security. This study used the pressure-state-response (PSR) model to vertically evaluate Yunnan's ecological security and horizontally compare ecological security between Yunnan and other four neighbouring provinces (Sichuan, Chongqing, Guizhou, Guangxi) during 2000–2020. We also elaborated on the ecological security of Yunnan's unique geographical features, such as plateau lakes, karst mountains, and tropical rainforest areas. The results show that the ecological security in Yunnan Province improved overall, with a slow increase (2000–2006), a fluctuating decline (2007–2012), and a sharp jump (2013–2020). The ecological security level climbed from 'critical safe' to 'comparative safety'. The pressure layer was the largest contributor to the increase from 2000 to 2011, whereas the response layer was the main determinant of the upward trend since 2012. Despite its better performance early in the study period, Yunnan's ecological security index (ESI) rose at a lower rate since 2011 than ESIs of neighbouring provinces in the southwest. Within Yunnan, unique geographical regions have roughly consistent ESIs as the entire province. The exception was the tropical rainforest area, with lower ESI than in other parts of Yunnan. We then discussed implications for enhancing ecological security in Yunnan, including real-time monitoring platforms, green innovations and different environmental regulations. The results provide insight beneficial to the improvement of ecological-security evaluation and the ecological sustainable development of Yunnan. [ABSTRACT FROM AUTHOR]