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.

Keywords: 16S rRNA gene; Illumina MiSeq; bacterial composition; bacterial diversity; billings reservoir.

Figure 1

Map showing sampling site locations in the Billings Reservoir in São Paulo. The map was generated using QGIS 3.22.0 (Redlands, CA, USA).

Figure 2

Bootstrap observation biplots derived from the principal component analysis (PCA) of the Billings water physicochemical properties and α bacterial diversities represented by the chao1 and Shannon indices based on 100 resamples of the data. The two principal components (PC1 and PC2) explained 46.3% of the total variation in the environmental data. Temperature (Temp), dissolved oxygen (DO), phosphorus (P), ammonia (NH³⁺), and nitrate (NO^3-). Green lines represent the correlation coefficient between the PC scores and each environmental parameter. Black dots represent sampling points from the bottom layers, and blue squares represent sampling points from the surface water.

Figure 3

Bacterial community alpha diversity as calculated by the phylogenetic diversity index of water samples from the surface and bottom layers. The error bars indicate the mean with standard error.

Figure 4

The relative abundance of (A) Proteobacteria and (B) Bacteroidetes, and (C) relative abundance of bacterial composition at the phylum level of the surface and bottom layers.

Figure 5

Relative abundance of bacterial composition at the genus level of the surface and bottom layers.