Optimization of influential nutrients during direct cellulose fermentation into hydrogen by Clostridium thermocellum.

Nazim Cicek,David Levin,Rumana Islam,Richard Sparling

doi:10.3390/ijms16023116

Abstract

Combinatorial effects of influential growth nutrients were investigated in order to enhance hydrogen (H2) production during direct conversion of cellulose by Clostridium thermocellum DSM 1237. A central composite face-centered design and response surface methodology (RSM) were applied to optimize concentrations of cellulose, yeast extract (YE), and magnesium chloride (Mg) in culture. The overall optimum composition generated by the desirability function resulted in 57.28 mmol H2/L-culture with 1.30 mol H2/mol glucose and 7.48 mmol/(g·cell·h) when cultures contained 25 g/L cellulose, 2 g/L YE, and 1.75 g/L Mg. Compared with the unaltered medium, the optimized medium produced approximately 3.2-fold more H2 within the same time-frame with 50% higher specific productivity, which are also better than previously reported values from similar studies. Nutrient composition that diverted carbon and electron flux away from H2 promoting ethanol production was also determined. This study represents the first investigation dealing with multifactor optimization with RSM for H2 production during direct cellulose fermentation.

Highlights

Rising global concerns about climate change coupled with accelerated energy consumption has propelled the search for clean and sustainable alternatives to fossil fuels
Combinatorial effects of the three medium nutrients, cellulose, yeast extract (YE) and magnesium chloride (Mg) on volumetric and molar yields of hydrogen were studied with a CCF design
The primary response, concentration of H2, was presented in Table 1 along with substrate specific and cell-mass specific yields of H2 calculated based on total glucose equivalents converted into end-products (Gp)

Summary

Introduction

Rising global concerns about climate change coupled with accelerated energy consumption has propelled the search for clean and sustainable alternatives to fossil fuels. Despite a ten-fold reduction in the cost of cellulase enzyme production, the projected cost for consolidated bioprocessing (CBP) was estimated to be lower than SSF and similar configurations requiring dedicated enzyme production [2,3,5]. Technological challenges such as low volumetric production rates and low product-tolerance of fermenting organisms impose major bottlenecks to commercialize cellulosic H2 production through CBP and substantial research efforts are required for successful commercialization [3,5]

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Results

Conclusion