Bacteria from the sewer can become producers of hydrogen fuel

Scientists from the Federal Research Centre “Fundamentals of Biotechnology” of the Russian Academy of Sciences studied bacterium discovered in a wastewater treatment bioreactor. This microorganism has adapted to life in an acidic environment and breaks down carbohydrate-rich organic waste to form hydrogen. The bacterium was named SP-H2 and turned out to be the new strain of Thermoanaerobacterium thermosaccharolyticum. The features of this bacterium and its potential in the production of hydrogen fuel, the scientists described in their paper in the International Journal of Hydrogen Energy.

Products of combustion of petroleum-based fuels in an internal combustion engine pollute the atmosphere, and oil prices are constantly rising. Hydrogen fuel could become an alternative to fossil fuels. When hydrogen is burned, no greenhouse gases are formed, the only product is water. The first hydrogen vehicles are already produced by such big car manufacturers as Audi, Toyota, Honda, Hyundai, Ford, BMW. Production of “green” hydrogen from renewable sources is more progressive and environmentally friendly compared to production from fossil fuels, which are rapidly depleted. Microorganisms are increasingly being used as microbial cell factories for the production of various chemicals and materials to achieve a sustainable chemical industry. Over millions of years of evolution, they have adapted to the assimilation of various substances and obtaining energy literally from the air, and often not only without it, but also without light. One of these microorganisms was studied by Russian scientists.

«It is estimated that only 0.001% of all extant microbial taxa have been discovered to date.  Even most of the microorganisms that surround us every day are difficult to culture in laboratories, so we knew little about them until the recent advent of new molecular genetic methods. More in-depth research in this field opens up an inexhaustible supply of enzymes and systems for obtaining a wide variety of substances and performing tasks for energy, pharmaceuticals, chemistry, agriculture and many other industries. One of such examples is a newly isolated strain of bacterium Thermoanaerobacterium thermosaccharolyticum, named SP-H2, which enables us to learn many facts about the production of hydrogen from organic compounds», – tells co-author of the study, the head of Laboratory of Microbiology of Anthropogenic Habitats of the Federal Research Centre “Fundamentals of Biotechnology” of the Russian Academy of Sciences, Yuriy Litti.

Scientists have found the DNA of a bacterium in wastewater that breaks down the building blocks of carbohydrates and produces hydrogen gas, as well as ethanol, acetate and butyrate. To figure out what kind of microorganism it is, the scientists conducted the analysis of 16S rRNA. In this section of the DNA sequence, a part of the ribosome is encoded – the structure responsible for protein assembly in the cell. The results showed that the bacterium belongs to a new strain of Thermoanaerobacterium thermosaccharolyticum. It was found to be a thermophilic microorganism, optimally growing at a temperature of 55-60°C in a slightly alkaline environment with a pH level of 7.5.

Scientists carried out experiments to find out which substrates are consumed by SP-H2 with the highest production of hydrogen. The “menu” of SP-H2 included both hexoses, such as maltose, glucose, mannose, fructose, lactose, galactose, saccharose, raffinose, cellobiose, and pentoses (xylose and arabinose). Scientists also tested if the bacterium feels good in the real industrial wastewater, rich in organics: cheese whey, confectionery wastewater, and sugar-beet processing wastewater. The highest hydrogen yield was observed from maltose, a bit less – from lactose and cellobiose. Cheese whey and confectionery wastewater turned out to be the best industrial wastewater for hydrogen production.

“To date, the low yield of the target product is still a problem that hinders the large-scale implementation of dark fermentative hydrogen production. On average, the process yields 1-2 moles of H₂ per mole of glucose. A part of organics, even under the most favorable conditions, will be left and avoid conversion. Moreover, acidic by-products accumulate during the reaction, which can drastically lower the pH and inhibit bacterial growth. In our studies, we achieved a yield of 1.91 mole of hydrogen per mole of hexose; the highest hydrogen production rate was observed during decomposition of xylose. Also, our studies have shown that Thermoanaerobacterim thermosacharolitycum SP-H2 can be considered a promising strain for obtaining hydrogen from wastewater, which is not affected by indigenous microorganisms. When we find a way to increase the yield of the target product, we can learn how to produce hydrogen fuel using biotechnology on an industrial scale”, – comments Yuriy Litti.