Environmental diversity of bacteria in a warm monomictic tropical freshwater lake

Diversity and Structure of the Prokaryotic Community in Tropical Monomictic Reservoir

Bacteria and Archaea are microorganisms that play key roles in the biogeochemical transformations that control water quality in freshwater ecosystems, such as in reservoirs. In this study, we characterize the prokaryotic community of a high-relevance tropical eutrophic reservoir using a 16S rRNA gene survey during a low-water level fluctuation period mainly used for storage, associating the distribution of these microorganisms with the hydrogeochemical conditions of the water column. Our findings revealed that diversity and structure of the prokaryotic community exhibited spatio-temporal variations driven by the annual circulation-stratification hydrodynamic cycle and are significantly correlated with the concentrations of dissolved oxygen (DO), soluble reactive phosphorus (SRP), and dissolved inorganic nitrogen (DIN). During the heterotrophic circulation, the breakdown of thermal gradient leads to a homogeneous distribution of the nutrients, where the presence of DO promotes the dominance of aerobic and facultative heterotrophic bacteria such as Bacteroidota, Actinobacteriota, and Verrucomicrobiota. Also, the autotrophic circulation was characterized by an increase of DO and NO3- concentrations, with abundant Cyanobacteria. Finally, during the stratification, the presence of prokaryotes associated with the metabolism of CH4 was detected, mainly in the hypolimnion, as well as others related to sulfate reduction and nitrification. This study shows the diversity of the prokaryotic community in tropical eutrophic reservoirs, and how the continuous monitoring with metabarcoding techniques can provide critical insights for a deeper understanding of the biogeochemical dynamics and improve the water resource management in the future.

Effects of Different River Crab Eriocheir sinensis Polyculture Practices on Bacterial, Fungal and Protist Communities in Pond Water

Microorganisms, including bacteria, fungi, and protists, are key drivers in aquatic ecosystems, maintaining ecological balance and normal material circulation, playing vital roles in ecosystem functions and biogeochemical processes. To evaluate the environmental impact of different river crab polyculture practices, we set up two different river crab (Eriocheir sinensis) polyculture practices: one where river crabs were cultured with mandarin fish (Siniperca chuatsi), silver carp (Hypophthalmichthys molitrix), and freshwater fish stone moroko (Pseudorasbora parva), and another where river crabs were cultured just with mandarin fish and silver carp. These two polyculture practices were referred to as PC and MC, respectively. We analyzed the water bacterial, fungal, and protist communities in the PC and MC groups using 16S, ITS, and 18S ribosomal RNA high-throughput sequencing. We found that the PC group obviously increased the diversity of microbial communities and altered their composition. The bacterial community held the narrowest habitat niche and exhibited the weakest environmental adaption compared to fungal and protist communities. The PC group altered the co-occurrence networks of bacteria, fungi, and protist, leading to more complex and stable communities of fungi and protist. Furthermore, the PC group shifted the assembly mechanism of the bacterial community from being predominantly deterministic to predominantly stochastic processes, with relatively minor impacts on the fungal and protist communities. Environmental factors, especially dissolved oxygen (DO), were significantly associated with the communities of bacteria, fungi, and protists, with DO being the major contributor to changes in the microbial communities. Our results suggest that the polyculture of river crab with mandarin fish, silver carp, and stone moroko was an effective and viable attempt, and it was superior in terms of microbial community diversity and stability.

Metagenomic signatures of a tropical mining-impacted stream reveal complex microbial and metabolic networks

Bacteria from aquatic ecosystems significantly contribute to biogeochemical cycles, but details of their community structure in tropical mining-impacted environments remain unexplored. In this study, we analyzed a bacterial community from circumneutral-pH tropical stream sediment by 16S rRNA and shotgun deep sequencing. Carrapatos stream sediment, which has been exposed to metal stress due to gold and iron mining (21 [g Fe]/kg), revealed a diverse community, with predominance of Proteobacteria (39.4%), Bacteroidetes (12.2%), and Parcubacteria (11.4%). Among Proteobacteria, the most abundant reads were assigned to neutrophilic iron-oxidizing taxa, such as Gallionella, Sideroxydans, and Mariprofundus, which are involved in Fe cycling and harbor several metal resistance genes. Functional analysis revealed a large number of genes participating in nitrogen and methane metabolic pathways despite the low concentrations of inorganic nitrogen in the Carrapatos stream. Our findings provide important insights into bacterial community interactions in a mining-impacted environment.