Dynamics of bacterial community in Tonle Sap Lake, a large tropical flood-pulse system in Southeast Asia

doi:10.1016/j.scitotenv.2019.01.351

Science of The Total Environment

Volume 664, 10 May 2019, Pages 414-423

https://doi.org/10.1016/j.scitotenv.2019.01.351 Get rights and content

Highlights

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The Tonle Sap Lake bacterial community differed between the water and sediment.
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The bacterial community abundance varied with location and season.
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Bacterial diversity in the deep-water increased during the transition season.
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The bacterial concentration condensed in the lake water during low-water periods.
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The floating villages' bacterial community differed from that at non-point sources.

Abstract

Tonle Sap Lake, the largest freshwater body in Southeast Asia, plays an important role in lives and environment. The lake is reportedly under anthropogenic pressure and suffers from eutrophication. The floating villagers suffer from waterborne diseases. However, the shift in bacterial community due to human activities in this great lake has not yet been reported. We aimed to determine the dynamics of the bacterial community and their concentration in the lake using 67 surface waters, 53 sub-layer waters and 59 sediment samples by Next Generation Sequencing (NGS). The bacterial communities in the surface water and sub-layer water were similar but they differed from the sediment; however, their abundance showed spatiotemporal variations. The bacterial diversity reached the highest value in the dry season but lowest value in the rainy season in the surface water and sediment. Their diversity in the sub-layer water was highest in the transition from dry to rainy season. The total 16S rRNA gene copy number in the sediment were >100 times higher than that measured in the water. The Cyanobacteria, Actinobacteria, and Proteobacteria concentrations in the lake water increased in the dry season and reached a peak in the transition from dry to rainy season. The concentrations of Proteobacteria and Firmicutes elevated in the lake water and sediment, respectively, in the floating villages which were >10 times higher than the places with non-point sources. The bacterial concentration and its diversity in the Tonle Sap Lake changed based on the lake water volume between rainy and dry season. The bacterial concentration in the Tonle Sap Lake diluted with the water inflow from Mekong River and its tributaries in the rainy season. As influenced by the fecal waste, the bacterial community in the floating villages differed from the places with non-point source.

Graphical abstract

Introduction

The role of the bacterial community in the environment is essential for its well-being. However, the establishment of the bacterial community in the water environment may vary from location to location depending on the community adaptation, environmental factors, and human activities (Guo et al., 2019; Newton et al., 2011; Wang et al., 2018). Many studies investigated the seasonal changes of bacterial community in the temperate aquatic based on the relative abundance of different bacterial groups (Chen et al., 2016; Li et al., 2015; Tang et al., 2017; Wan et al., 2017). The interpretation of the results based on only the relative abundance of each bacterial group may not properly describe its spatiotemporal changes in a flood-pulse system lake. Comparing to the temperate aquatic environment, the tropical aquatic environment was known as a pool supporting a diverse species and play a vital role in the food demands. However, the dynamics of bacterial community in the tropical lake environment, which located in the developing country, are poorly understood (Abia et al., 2018; Pajares et al., 2016). In addition, the common dataset of a bacterial community shifting in the different water depths and sediment in the aquatic water is not well characterized since the studies have been focused on the individual surface water or sediment (Chen et al., 2016; Hengy et al., 2017; Li et al., 2017; Li et al., 2015; Liu et al., 2013; Wan et al., 2017).

Tonle Sap Lake, located in tropical climate in Cambodia, is known as a unique flood-pulse and the largest body of freshwater in Southeast Asia. This lake covers an area of 2500 km² during the dry season and expands up to 16,000 km² during the rainy season, serving the benefits for life and environmental ecosystem. The water in the lake exchange periodically with the Mekong River water. During the rainy season from May to October, the water flows from the swollen Mekong River into the Tonle Sap Lake via Tonle Sap River, while the flow is reversed during the dry season from December to April. Due to this natural phenomenon, the water quality in the Tonle Sap Lake change from season to season (Irvine et al., 2011). The lake is reportedly under-pressure due to the inflow of anthropogenic pollutants (Brooks et al., 2007; Holtgrieve et al., 2013; Lin and Qi, 2017). Over 1.7 million people who live and depend on the Tonle Sap Lake have no choice but to discard their household and human wastes into the lake (Brown et al., 2010; Holtgrieve et al., 2013). Moreover, due to the lack of wastewater treatment facility in the country, the sewages are usually discharging into the water sources without the treatment. Such wastes affect the chemical and biological quality of the water environment greatly (Liao et al., 2019; Price et al., 2018) and paradoxically, have negative impacts on the floating villagers' health since they use the lake water for their daily life activities. Hundred cases of typhoid fever and pediatric bloodstream infections caused by pathogenic bacteria have also been documented in the hospitals in the region (Pham Thanh et al., 2016; Stoesser et al., 2013).

Even, the water cycle in this great lake is unique between rainy and dry season and the lake was reportedly under anthropogenic pressure, the dynamics of bacterial community in this great lake are unknown. We therefore conducted this study to investigate on the dynamics of the bacterial community in the Tonle Sap Lake based on their relative abundance and absolute concentration at the different water depths and sediment. To determine the bacterial community structure and community similarity within the lake, we used next-generation sequencing (NGS) analysis and non-metric multidimensional scaling (NMDS), respectively. Total 16S rRNA gene copy number was determined using real-time quantitative polymerase chain reaction (qPCR).

Section snippets

Study sites and sample collection

We designed the sampling sites at seven cross-sections (CS) from the northwestern to the southeastern part of Tonle Sap Lake and in three floating villages [Kampong Plouk (KP), Kampong Luong (KL), and Chhnok Tru (CT)] (Fig. 1). We collected samples on four sampling dates for one year, beginning in December 2016 (Dec-16, transition from rainy to dry season), March 2017 (Mar-17, dry season), June 2017 (Jun-17, transition from dry to rainy season), and August 2017 (Aug-17, rainy season). The

Sample characteristics

The depth and water quality of Tonle Sap Lake varied based on the locations and seasons (Table 1). During our sampling, the water depth of the lake ranged from 0.56 m in the dry reason to 9.85 m in the rainy season. The water temperature, EC, DO, and pH were increased in the low-water period (Mar-17 and Jun-17) while they were decreased in the high-water period (Dec-16 and Aug-17). In contrast, during the high-water period, ORP was higher than during the low-water period. The ORP was measured

Discussion

Under anthropogenic pressure, the Tonle Sap Lake bacterial community experienced in the eutrophication and stressors from the biological and chemical pollutants. However, the natural phenomenon of the water cycle in this great lake serves many benefits for the lake water quality. A high abundance of Actinobacteria, Proteobacteria, and Cyanobacteria were found in the water samples in the Tonle Sap Lake and their concentration varied spatiotemporally. Based on the relative abundance value,

Conclusions

The dynamics of bacterial community in the largest tropical flood-pulse system in Southeast-Asia, such as Tonle Sap Lake, were quantified by NGS and qPCR in this study. The concentration of bacteria and its diversity in the lake changed seasonally based on the water volume of the lake. The bacterial community in the lake water differed from the lake sediment. As a unique hydrologic condition, the bacterial diversity in the sub-layer water reached the highest value in the transition from dry to

Conflict of interest statement

The authors declare that they have no conflict of interest.

Acknowledgments

This research was supported by the Science and Technology Research Partnership for Sustainable Development (SATREPS), the Japan Science and Technology Agency (JST)/Japan International Cooperation Agency (JICA), and the ASEAN University Network-Southeast Asia Engineering Education Development Network (AUN/SEED-Net).

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Dynamics of bacterial community in Tonle Sap Lake, a large tropical flood-pulse system in Southeast Asia

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Study sites and sample collection

Sample characteristics

Discussion

Conclusions

Conflict of interest statement

Acknowledgments

Sci. Total Environ.

Biol. Conserv.

J. Environ. Sci.

Water Res.

Water Res.

Sci. Total Environ.

Sci. Total Environ.

Water Res.

Sci. Total Environ.

Environ. Res.

Sci. Total Environ.

Microbiology

Sci. Total Environ.

Environ. Pollut.

Competitive survival of Escherichia coli, Vibrio cholerae, Salmonella typhimurium and Shigella dysenteriae in riverbed sediments

Microb. Ecol.

Genomic resolution of linkages in carbon, nitrogen, and sulfur cycling among widespread estuary sediment bacteria

Microbiome

Sanitation in Floating Communities in Cambodia

Legume symbiotic nitrogen fixation by beta-proteobacteria is widespread in nature

J. Bacteriol.

Key roles for freshwater Actinobacteria revealed by sub-layer metagenomic sequencing

Mol. Ecol.

Microbial community diversity patterns are related to physical and chemical differences among temperate lakes near Beaver Island, MI

PeerJ