by Hannah Van Dusen | Edited by Cecilia Kim
As the largest carbon dioxide reservoir in the world, the ocean contains a large portion of the greenhouse gasses produced by society. Oceans store far more carbon than both the atmosphere and terrestrial biosphere, and their amount of carbon dioxide continues to rise with increased emissions, largely from the burning of fossil fuels. Because carbon dioxide readily dissolves in water to produce carbonic acid, it has permeated the world’s oceans and heightened ocean acidification, posing threats to marine wildlife, oceanic resources, the climate, and human health.
In a 2021 Nature paper titled “Photoferrotrophy and phototrophic extracellular electron uptake is common in the marine anoxygenic phototroph Rhodovulum sulfidophilum,” scientists explored the role of bacteria known as photoferrotrophs in mitigating the climate change crisis. Previously studied in freshwater bacteria, photoferrotrophy involves nonoxygen evolving phototrophs, which grow by using light to couple the oxidation of ferrous iron, or Fe (II), with carbon dioxide fixation. In addition to performing photoferrotrophy, photoferrotrophs are able to utilize electrons from certain conductive minerals through a process known as phototrophic extracellular electron uptake (pEEU). Scientists have found, through preliminary studies, that phototrophs can perform carbon dioxide fixation through pEEU as well.
In the specific study delineated by Nature, researchers studied the marine bacteria Rhodovulum sulfidophilum, looking specifically at its AB26 strain. From this study, the researchers found that Rhodovulum sulfidophilum was capable of both photoferrotophy and pEEU, which provided evidence that these processes extend beyond solely freshwater bacteria. The researchers also found that the oxidation of iron by the photoferrotroph microbes is connected to the cycling of other elements such as carbon, nitrogen, and sulfur, crucial for maintaining marine sediment. Marine sediments make up the Earth’s largest ecosystem and allow for around half of global primary productivity, or the synthesis of organic compounds from aqueous and atmospheric carbon, to occur. Although the mechanisms behind photoferrotophy and pEEU and their role in primary productivity are still not entirely known, photoferrotrophs may have important impacts on reducing the amount of excess carbon in the ocean created by climate change.
Climate change, specifically increased levels of carbon dioxide, are detrimental to human health, being linked to conditions such as inflammation, reduced cognitive abilities, bone and kidney problems, and respiratory issues, amongst other problems. Furthermore, the vast amount of carbon dioxide in the oceans affects marine biodiversity and reduces the composition of the seafood that humans consume. Specifically, ocean acidification causes negative impacts on the development of various kinds of fish and how much protein or lipid they contain, meaning that fish may not be able to provide the omega-3 fatty acids essential to human health. In areas of the world where people rely heavily on the consumption of fish, this creates consequences for their food source. Moreover, ocean acidification causes ocean water to become increasingly toxic, affecting the drinking supply in certain places.
Beyond investigating the marine bacteria Rhodovulum sulfidophilum, scientists have also explored the abilities of other kinds of bacteria to fight climate change, with certain kinds being able to reduce methane emissions, sequester carbon in the soil, clean up oil spills, and produce sustainable biofuels. With the effects of climate change and increased levels of carbon dioxide in the atmosphere and oceans leading to serious effects on human health, the use of these microorganisms may be critical in keeping the Earth a safe and sustainable place to live.