Characterization of Bacterial Communities from the Surface and Adjacent Bottom Layers of Water in the Billings Reservoir

Abstract

Here, we describe the bacterial diversity and physicochemical properties in freshwater samples from the surface and bottom layers of the Billings Reservoir, the largest open-air storage ecosystem in the São Paulo (Brazil) metropolitan area. Forty-four samples (22 from the surface and 22 from the bottom layers) were characterized based on 16S rRNA gene analysis using Illumina MiSeq. Taxonomical composition revealed an abundance of the Cyanobacteria phylum, followed by Proteobacteria, which were grouped into 1903 and 2689 different genera in the surface and the deep-water layers, respectively. Chroobacteria, Actinobacteria, Betaproteobacteria, and Alphaproteobacteria were the most dominant classes. The Shannon diversity index was in the range of 2.3–5.39 and 4.04–6.86 in the surface and bottom layers, respectively. Flavobacterium was the most predominant pathogenic genus. Temperature and phosphorus concentrations were among the most influential factors in shaping the microbial communities of both layers. Predictive functional analysis suggests that the reservoir is enriched in motility genes involved in flagellar assembly. The overall results provide new information on the diversity composition, ecological function, and health risks of the bacterial community detected in the Billings freshwater reservoir. The broad bacterial diversity indicates that the bacterioplankton communities in the reservoir were involved in multiple essential environmental processes.

Temporal patterns of bacterial communities in the Billings Reservoir system

“…Previous studies primarily focused on physicochemical variables and the presence of bacterial strains using culture-dependent methods 22 , 26 – 29 . Recent culture-independent studies conducted by our group revealed a higher prokaryotic diversity in Billings Reservoir compared to similar water systems and also a high abundance of cyanobacteria 24 , 30 . These bacteria are considered the most widespread photosynthetic organisms due to their global distribution and their significant ecological presence in nutrient-rich habitats, which often lead to the formation of blooms 31 .…”

“…At the beginning of the study, the geographic coordinates of the collection sites were recorded to ensure that subsequent water samples and measurements were taken on water from specific locations. Collected samples were stored in cool boxes at 4 °C in the dark and transported to the laboratory, where they were immediately processed as previously described 24 , 30 . The number of sites on the reservoir and their locations are shown in Fig.…”

“…DNA was extracted from approximately 600 µl of each concentrated water sample by centrifugation of the surface water samples as detailed in our recently published study 24 . The PowerSoil DNA isolation kit (Mobio Laboratories Inc., Carlsbad, CA, USA) was used according to the manufacturer's protocol.…”

“…São Paulo, the largest urban area in Brazil, faces water stress with an annual water availability of less than 1,700 m3 per person in the São Paulo Metropolitan Region (SPMR) 23 . The Billings Reservoir, a significant freshwater source for the SPMR, serves multiple functions, including irrigation and flood control 24 . Despite its importance, the microbial community structure within the Billings Reservoir has been understudied since its construction in 1940 25 .…”