Methane penetration refers to a submersible area around the globe where the natural gas you rely on for cooking and heating is known as methane that leaks from the seabed. These penetrations are commonly found in transitional regions where land meets the ocean, known as the continental margin. Methane originates from and is produced by organic matter, including dead plants and animals, that have been buried under layers of sediment for millions of years. Through pressure and heat from within the Earth, this organic matter can decompose into methane, which escapes from the seabed into the ocean.

This methane also serves as an energy source for various microscopic organisms, allowing it to fuel your stove. The microorganisms known as methanogenic bacteria or methanotrophs utilize methane as food through a process referred to as aerobic methane oxidation. These bacteria employ oxygen to extract energy from methane gas, akin to how humans extract energy from food, producing carbon dioxide and water as by-products.

When carbon dioxide interacts with water, it creates a weak acid known as carbonic acid. Carboxylic acids can dissolve calcium carbonate minerals that make up shells in organisms like corals, mussels, and clams. While methanotrophs produce carbon dioxide as waste, scientists remain uncertain about its role in corroding calcium carbonate in marine environments. Research has been conducted in laboratories, but not in natural marine settings until now.

A team of researchers from Germany investigated the corrosion of calcium carbonate associated with active methane along the continental margin off the west coast of Gabon, Congo, and Angola in Africa. They deployed limestone cubes measuring 10 cm (around 4 inches) high and 4 cm (approximately 4 inches) wide above the seabed near active methane sites, as well as on a mussel bed. The cubes were left on the seabed for 2.5 years before being retrieved.

Upon recovery, the researchers noted that cubes situated near the methane leak exhibited rough surfaces. Microscopic examination revealed small holes, termed microborings, likely created by microorganisms. In contrast, cubes placed farther from the methane leak showed no signs of such features. This led researchers to interpret these differences as evidence that microorganisms are responsible for the dissolution of limestone in areas of methane penetration.

To further analyze the role of methanotrophs in limestone dissolution, the team extracted DNA from microbial communities inhabiting the limestone cubes. They identified DNA from members of aerobic methane-oxidizing bacteria, particularly from the uncultured HYD24-01 clade. Previous studies have detected these microorganisms in other methane-rich locations, suggesting their potential for corroding limestone.

To corroborate their findings, the researchers also examined lipid molecules known as lipid biomarkers from microorganisms at the site. Scientists utilize lipid biomarkers to identify bacterial species and their energy sources. They discovered that the lipid biomarkers collected from the seabed sites matched the DNA results. Notably, they found an abundance of lipids from methanotrophs called NC16:1Ω7 among the limestone cubes. This led them to conclude that methanotrophs prominently represented the microbial communities linked to the microborings in the limestone.

The research team proposed that their findings provide concrete evidence that methane-consuming bacteria dissolve calcium carbonate rocks in areas of marine methane. They suggested that these bacteria acidify their environment by releasing carbon dioxide during methane oxidation. The released carbon dioxide combines with water to form carbonic acid, which decreases pH levels, dissolves limestone, and contributes to ocean acidification. They advocated for future research to delve into the specific mechanisms that these microorganisms utilize and to quantify the extent of microbial erosion’s contribution to marine acidification.

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