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For centuries, the world has relied on fossil fuels for energy, however, over this time, their negative impact on the environment has become evident, including their effect on air and water pollution, and consequently, climate change. For the first time ever, in 2023, the global energy-related greenhouse gas emissions reached over 40 gigatonnes with carbon dioxide being the main culprit contributing to 87% of the total [1]. Renewables have become a more environmentally friendly alternative and, in 2023, consumption of renewable energy increased at 6 times the rate of total primary energy consumption [1]. Scientists have pursued more sustainable alternatives, including the use of hydrogen-producing bacteria.
Hydrogen is a promising alternative to fossil fuels [2] ; it has an energy yield of 286 kJ/mol, higher than any hydrocarbon fuel, and has no greenhouse impact as only heat and water are produced on combustion [2]. Various microorganisms produce hydrogen by dark fermentation, a catabolic process whereby sugars and proteins are metabolized to carboxylic acids, organic solvents and hydrogen gas [2]. Among these organisms are Clostridium, Enterobacter and Citrobacter species, but Clostridium is the most widely studied [2]. Scientists are continuing this avenue of research by attempting to isolate biohydrogen-producing bacteria from bioreactors and natural environments such as land and water.
Huyen et al. investigated the fermentative hydrogen producing potential of bacteria isolated from sludge as well as identifying the most suitable conditions for ultimate hydrogen production using different culture conditions [2]. Sludge was sampled from the To Lich River in Hanoi, Vietnam; they ensured that their sample was from the deepest layer possible to maximise their yield of potential anaerobes [2]. For bacterial isolation, they used Peptone Yeast Extract medium and incubated samples in a Whitley A55 Workstation [2]. After 48 hours, colony types were analysed based on their shape, colour, size, elevation etc., as well as their physio-biochemical characteristics [2]. Genotypic analysis was also carried out using 16S rRNA nucleotide sequencing [2]. From 2 samples, they successfully isolated 3 Clostridium spp. and continued their research with strain CS3, which demonstrated the highest hydrogen formation ability [2]. Using 16S rRNA sequencing and BLAST, they found that this strain had 99.8% similarity to Clostridium sulfidigenes SGB2, so they named their strain C. sulfidigenes CS3 with accession number SUB14851242 in GenBank [2]. CS3 shares many physiological traits with its closest relative including motility, oxidase absence and endospore formation, further supporting the notion that strain CS3 was a Clostridium sp. [2]. Among the many methods tested, a maximum hydrogen yield of 2.1 mol H2/mol glucose was obtained at pH 7.0 and 37°C for 48 hours with agitation at 200 rpm [2]. This strain shows positive potential for biohydrogen fermentation and therefore, a promising sustainable alternative to fossil fuels.
Sustainability promotes ecological, human and economical health and is a social goal that is becoming predominant among people and businesses. Therefore, it is likely that research of this kind will be among the many studies attempting to aid environmentally friendly practices using microbiology.
Written by DWS Microbiologist Kirsty McTear
References
- Energy Institute. Statistical Review of World Energy [Internet]. Statistical review of world energy. 2024. Available from: https://www.energyinst.org/statistical-review
- Huyen NTT, Trang NH, Ha BTV. Isolation and Characterization of a New High-Yield Hydrogen-Producing Strain, Clostridium sulfidigenes CS3, from Anaerobic Sludge in the To Lich River. VNU Journal of Science: Natural Sciences and Technology. 2024 Dec 9
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