Enhanced hydrogen production of Rhodobacter sphaeroides promoted by extracellular H+ of Halobacterium salinarum

Jiang-Yu Ye,Yi-Chao Wang,Yue Pan,Yong Wang

doi:10.1186/s13213-021-01621-z

Abstract

PurposeThis study utilized the principle that the bacteriorhodopsin (BR) produced by Halobacterium salinarum could increase the hydrogen production of Rhodobacter sphaeroides. H. salinarum are co-cultured with R. sphaeroides to determine the impact of purple membrane fragments (PM) on R. sphaeroides and improve its hydrogen production capacity.MethodsIn this study, low-salinity in 14 % NaCl domesticates H salinarum. Then, 0–160 nmol of different concentration gradient groups of bacteriorhodopsin (BR) and R. sphaeroides was co-cultivated, and the hydrogen production and pH are measured; then, R. sphaeroides and immobilized BR of different concentrations are used to produce hydrogen to detect the amount of hydrogen. Two-chamber microbial hydrogen production system with proton exchange membrane-assisted proton flow was established, and the system was operated. As additional electricity added under 0.3 V, the hydrogen production rate increased with voltages in the coupled system.ResultsH salinarum can still grow well after low salt in 14% NaCl domestication. When the BR concentration is 80 nmol, the highest hydrogen production reached 217 mL per hour. Both immobilized PC (packed cells) and immobilized PM (purple membrane) of H. salinarum could promote hydrogen production of R. sphaeroides to some extent. The highest production of hydrogen was obtained by the coupled system with 40 nmol BR of immobilized PC, which increased from 127 to 232 mL, and the maximum H2 production rate was 18.2 mL−1 h−1 L culture. In the 192 h experiment time, when the potential is 0.3 V, the hydrogen production amount can reach 920 mL, which is 50.3% higher than the control group.ConclusionsThe stability of the system greatly improved after PC was immobilized, and the time for hydrogen production of R. sphaeroides significantly extended on same condition. As additional electricity added under 0.3 V, the hydrogen production rate increased with voltages in the coupled system. These results are helpful to build a hydrogen production-coupled system by nitrogenase of R. sphaeroides and proton pump of H. salinarum.Graphical abstract

Highlights

Rhodobacter sphaeroides is one of the most famous nonsulfur purple bacteria for its capability of using a wide variety of substrates and its high activity in hydrogen production under anaerobic condition (Asada et al 2006; Koku et al 2003; Laurinavichene et al 2018; Yetis et al 2000)
Acclimation and growth of H. salinarum H. salinarum generally lives in salt evaporation ponds, natural salt lakes, and other hyperhaline environments, where the salt concentration comes close to saturation
The experimental results indicated that the cells of H. salinarum were well-grown in salinity of 17~ 25% (2.91– 4.27 mol/L), and its vitality would drop quickly at salinities below 17%

Summary

Introduction

Rhodobacter sphaeroides is one of the most famous nonsulfur purple bacteria for its capability of using a wide variety of substrates and its high activity in hydrogen production under anaerobic condition (Asada et al 2006; Koku et al 2003; Laurinavichene et al 2018; Yetis et al 2000). In the absence of nitrogen, the nitrogenase in R. sphaeroides can produce molecular hydrogen with protons under anaerobic condition (Zabut et al 2006). H. salinarum is a model organism in the halophilic branch of the archaea, which can live in saturated salt solutions (4 mmol salt or higher) It can live with light as the only energy source due to its activity of the retinal protein bacteriorhodopsin (BR), a light-driven proton pump. Its packed cells (PC) or PM might be combined with the other system for producing hydrogen (Khan and Bhatt 1997; Sediroglu et al 1999; Frank et al 2016; Zabut et al 2006)

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