Metagenomic and metabolomic analysis of a bryozoan-associated microbial complex from the Hanjiang River, China

BACKGROUND: Bryozoans are ancient colonial animals that have existed for over 470 million years and are widely distributed across aquatic environments. Recently, many spherical colloids (average diameter≈1 meter in diameter), containing bryozoans and diverse microorganisms, were found in the Hanjiang river in China. In this study, we investigated these bryozoan-dominated microbial complexes using metagenomic sequencing, metabolomic profiling, and complementary approaches. RESULTS: The results revealed that the microbial structure dominated by bryozoans included eukaryotes such as fungi, microalgae, as well as prokaryotes such as bacteria, and acellular entities such as viruses. All members form a highly integrated consortium that collaboratively maintains community function and stability, which displayed the shape and structure of a regular microbial complex and increased in size. Additionally, the results suggested the predominately presence of Proteobacteria were particularly abundant and are known to produce bryozoans in response to bryozoan signals. Interesting, it was implied that a decrease or even a loss in virulence occurs when pathogenic microorganisms become members of the complex. This is the first study focusing on the composition and metabolites of the unusual microorganism complex. The results discovered the close and intriguing connections within the microbial communities dominated by the ancient organism bryozoan through multi-omics technologies. It showed that both eukaryotes and prokaryotes can coordinate, thereby forming a stable composite structure.