Bacterial communities from components of freshwater microcosms
Nutrient cycling and organic matter transformations are primarily performed by microorganisms in aquatic systems, but are further facilitated through the mixing of sediment by macroinvertebrates. The impact of macroinvertebrates and their microbiome on the water column of freshwater systems has largely been understudied, but is likely to alter both bacterial community function and composition. A microcosm design was used to study the impact that an invasive freshwater clam, Corbicula fluminea (Corbicula), and the crayfish, Procambarus vioscai paynei (crayfish), have on the microbial community of their water column and how this affects the enzyme activity within the system. Enzymes involved in the breakdown of organic carbon (B-glucosidase), phosphorus (phosphatase), and carbon and nitrogen (N-acetyl-glucosidase; NAGase) were assayed over a four-day duration, and the external microbiome of each invertebrate was characterized using Illumina 16S rRNA gene sequencing. Both crayfish and bivalves significantly altered the structure and function of the bacterial community in the water column of microcosms. Crayfish were found to stimulate enzyme activity more than bivalves, while Corbicula at higher densities were found to increase enzyme activity in systems compared to lower densities. The external microbiomes of macroinvertebrates were not found to be a significant source to the bacterial communities of vegetation or the water column. These results support the significance that macroinvertebrate function and density impact biogeochemical processes in freshwater ecosystems, particularly in the water column of the system. Further research on quantifying biogeochemical processes in freshwater systems should consider all components of the environment and how they impact one another. This study contributes to a deeper understanding of the relationships between macroinvertebrates and the microbial communities of their environment, with specific implications to the water column, a frequently overlooked component of these systems. Understanding the dynamic of all system components is crucial to managing and conserving freshwater ecosystems, especially in the face of escalating environmental pressures.