Stratification Modelling of Key Bacterial Taxa Driven by Metabolic Dynamics in Meromictic Lakes

Kaicheng Zhu,Haibin Su,Federico M Lauro

doi:10.1038/s41598-018-27973-2

Abstract

In meromictic lakes, the water column is stratified into distinguishable steady layers with different physico-chemical properties. The bottom portion, known as monimolimnion, has been studied for the functional stratification of microbial populations. Recent experiments have reported the profiles of bacterial and nutrient spatial distributions, but quantitative understanding is invoked to unravel the underlying mechanism of maintaining the discrete spatial organization. Here a reaction-diffusion model is developed to highlight the spatial pattern coupled with the light-driven metabolism of bacteria, which is resilient to a wide range of dynamical correlation between bacterial and nutrient species at the molecular level. Particularly, exact analytical solutions of the system are presented together with numerical results, in a good agreement with measurements in Ace lake and Rogoznica lake. Furthermore, one quantitative prediction is reported here on the dynamics of the seasonal stratification patterns in Ace lake. The active role played by the bacterial metabolism at microscale clearly shapes the biogeochemistry landscape of lake-wide ecology at macroscale.

Highlights

We simplify the metabolism to involve only one type of nutrient and one type of end-product for each bacterial species, and the metabolic reactions are explicitly written in simple pathways: B + N B ⋅ N → αB + W, B → ∅, and B ⋅ N → ∅, where B stands for the bacterium, N for the nutrient, and W for the waste
From the coarse-grained pathways of the green sulfur bacteria (GSB)-sulfur-reducing bacteria (SRB) sulfur cycle (Fig. 1b), the reaction terms in the partial differential equation (PDE) reflect the rate of photosynthesis of GSB, the sulfate-reduction rate by SRB, and the mortality rate of individual bacterial populations
The anoxygenic photosynthesis of GSB requires a supply of photons, resulting in two different metabolic states of GSB: one active-photosynthesis state near the top of the monimolimnion and one inactive-photosynthesis state deeper in the lake where light is highly attenuated

Summary

Dynamics in Meromictic Lakes

The water column is stratified into distinguishable steady layers with different physico-chemical properties. The model covers the light supply factor of the anoxygenic photosynthesis in the sulfur cycle to illustrate the light-driven mechanism of the spatial pattern shifting We apply both analytical and numerical methods and compare our simulated results with the experimental observations of two meromictic lakes from different biomes: Ace lake and Rogoznica lake[3,7,9]. The simplicity of this mathematical model provides an intuitive understanding of the macroscale spatial organization of the bacterial landscape depending on the microscale metabolic activity. Since Eqs (4) and (5) are based on the steady-state assumption, these relations describe the spatial patterns on macro timescales where the bacterium-nutrient system is in or near the equilibration

Results and Discussion

Conclusions

Additional Information