Transformations of Diatom-Derived Dissolved Organic Matter by Bacillus pumilus Under Warming and Acidification Conditions.

Yang Liu,Jun Sun,Xueru Wang

doi:10.3389/fmicb.2022.833670

Abstract

Heterotrophic bacteria are assumed to play an important role in processing of phytoplankton-derived dissolved organic matter (DOM). Although the algae-derived organic matter is commonly studied, the transformation and processing of DOM by epiphytic bacteria for phytoplankton have rarely been investigated, especially under warming and acidification. In this study, Bacillus pumilus is used to explore the ecologically important marine diatom Skeletonema dohrnii-derived DOM under different conditions (temperature, 27°C and 31°C; pCO2, 400 and 1,000 ppm), utilizing fluorescence excitation-emission matrix (EEM) combined with parallel factor analysis (EEM-PARAFAC). Fluorescence regional integration and the peak selecting method are used to generate B, T, N, A, M, and C peaks in the EEM fluorescence spectroscopy. The main known fluorophores including that protein-like components (peaks B and T), unknown components (peak N), and humic-like component (peaks A, M, and C). Our experimental results showed that under higher temperature and pressure of CO2 (pCO2) conditions, S. dohrnii-derived DOM fluorescence was dominated by a protein-like signal that slower waning throughout the experiment, becoming an increasingly humic-like substance, implying that processing by the epiphytic bacteria (B. pumilus) produced more complex molecules. In addition, spectroscopic indices (e.g., fluorescence index, biological index, freshness index β/α, and humification index) were changed in varying degrees. This study reveals and confirms the direct participation of heterotrophic bacteria in the transformation and generation of algae-derived DOM in the laboratory, underlining the influence of global warming and ocean acidification on this process.

Highlights

The primary type of organic matter in the oceanic environment is phytoplankton-derived dissolved organic matter (DOM), which contributes to the world’s greatest carbon pool (662 Pg C) (Hansell et al, 2009, 2012)
We examined the characteristics of fluorescent organic matter by using excitation-emission matrix (EEM)-parallel factor analysis (PARAFAC) methods
The B. pumilus abundance changed at 30 days in all conditions (Figure 1A)

Summary

Introduction

The primary type of organic matter in the oceanic environment is phytoplankton-derived dissolved organic matter (DOM), which contributes to the world’s greatest carbon pool (662 Pg C) (Hansell et al, 2009, 2012). At a rate of 43 Tg per Bacterial Transformation and Processing of DOM year, more than 90% of dissolved organic carbon (DOC) could be generated, playing an essential role in the global carbon cycle (Thornton, 2014). For almost 200 million years, algae and bacteria have coexisted in aquatic environments (Falkowski et al, 2004). Heterotrophic bacteria are key biogeochemical regulators in aquatic systems. The majority of the DOM metabolism produced by algae enters the microbial cycle, where it provides carbon and nutrients to heterotrophic bacteria (Pomeroy et al, 2007). Heterotrophic bacteria link biogeochemical cycles together by decomposing and producing organic matter. Carbon consumption and transport rates of heterotrophic bacteria govern the efficacy of carbon sequestration in the ocean (Fuhrman, 2009)

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Results

Discussion

Conclusion