Can methane-eating bacteria in drylands help us reduce greenhouse gases?

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THE LARGEST TERRESTRIAL ECOSYSTEM ON EARTH:

DRYLANDS Drylands are characterized by scarce rainfalls and consequen tly do not have lush vegetation. However, drylands cover a whole range of diﬀerent ecosystems, from the driest place on Earth, the hot desert of Atacama in Chile, to the leafy eucalyptus forests in Austra lia where Koalas live (Figure /one.tnum./one.tnum). Dryland ecosystems also containhuge numbers of organisms, many of which are plants and animals that l ive only in drylands and have adapted to the harsh conditions. Dryland s are the biggest terrestrial ecosystem, occupying almost half of the Earth’s land surface (4five.tnum%) and are home to more than 4zero.tnum% of the human population. So, you can see why drylands are extremely important areas of the earth to research. Living beings and non-living substances in the environment, li ke plants and water, are intimately connected in by cycles in nature. These non-living substances are called abiotic factors. Water is ABIOTIC Non-living abiotic factors in an environment include temperature, water, and light. crucial for all processes that are related to life, from plant gr owth to the development of communities of soil microorganisms. There fore, water is the most important abiotic factor in an ecosystem. We measure the availability of water in an ecosystem with a measurement called aridity, a mathematical relationship between the amount of ARIDITY Mathematical relationship between the amount of precipitation (rain, fog, or snow) and the evaporation of water. It describes how deﬁcient water is in an ecosystem. precipitation (rain, fog, or snow) and the evaporation of water. The less available water there, the more arid a place is (Figure /one.tnum./one.tnum). In drylands, where water is not always available, the natural cycle s between living beings and non-living substances are hugely aﬀe cted. When there is no water from rain and the humidity goes down, this aﬀects the carbon (C) and nitrogen (N) cycles, reducing the abundance of these elements in soil, which impacts plants, animals, ABUNDANCE The number of individuals of a certain type present in an environment. and microorganisms. All this makes drylands extremely vulner able to ongoing climate change.

SOIL BACTERIA AND METHANE

The Earth is surrounded by a gaseous layer called the atmosphere , which protects us form solar radiation and helps maintain the overall temperature of the Earth. The principal components of the atmosphere are nitrogen (7eight.tnum%) and oxygen (2one.tnum%), but there are many other gases in the atmosphere as well. Some atmospheric gases, suc h as carbon dioxide (CO /two.tnum) and water vapor, are the greenhouse gases, so called because they trap the Sun’s heat, working like the glass in a greenhouse. The greenhouse gases let the Sun’s light reach the Earth’s surface but prevent heat from leaving the atmosphere. This trap ping of heat contributes to global warming. The most abundant human-produced greenhouse gas in the atmosphere is CO /two.tnum, released from burning fossil fuels. However, the second most important gas contributing to global warming is methane (CH /four.tnum). Methane is a simple molecule formed by one atom of carbon (C) and four atoms of hydrogen (H). The warming eﬀect of one molecule of methane is equivalent to 2five.tnum molecules of CO/two.tnum, making it a super-powerful greenhouse gas. Methane is produce d by methanogens, a group of microorganisms that do not need oxygen METHANOGENS Group of microorganisms that do not need oxygen to survive and therefore can live in oxygen-free environments. They produce methane while decomposing organic matter, such as leaves or wood fragments. to survive and therefore can live in oxygen-free environments l ike rice ﬁelds, lake sediments, and wetlands. Methanogens also live in the digestive tracts of animals, such as the stomachs of cattle and even in humans! Methanogens are responsible for animal burps and f arts! Methanogens also produce methane while decomposing organic matter, such as leaves or wood fragments. In addition to agriculture , other human activities, such as the oil and gas industries also rel ease large amounts of methane into our atmosphere [/one.tnum] (Figure /two.tnum). The methane released into the atmosphere is greatly contributing to climate change and there is only one group of organisms that can consume it, the methanotrophs. This group of microorganisms METHANOTROPHS Group of microorganisms that are capable of using up methane as their source of carbon and energy. They are methane eaters. is capable of using up methane as their source of carbon and energy. These microorganisms basically eat methane (Figure /two.tnum)! In drylands, methane production is low because of the scarcity of water (remember, methanogens typically live in ﬂooded soils and other oxygen-free environments). However, due to the large extent of drylands and the global increase of methane in the atmosphere, dryland ecosystems could be of great interest if methanotrophs a re also present and abundant there. Main methane (CH /four.tnum) sources and sinks.

HOW TO FIND AND STUDY METHANOTROPHS

In our research, we were interested in learning if methanotrophs are common in the soils of drylands worldwide, and if they are sensitive to climate conditions and soil properties, like most so il microorganisms. First, we selected 8zero.tnum dryland sites all around the world (Figure /one.tnum./one.tnum). At each site, we collected climate information, such as mean annual temperature, annual precipitation, and aridity. W e also took soil samples and analyzed properties, such as the amount of organic matter (Organic Carbon), pH, and sand content (Figure /one.tnum./two.tnum). High soil organic matter indicates the soil is fertile, meaning it has the nutrients that plants, soil animals and microorganisms need to grow. pH analysis tells us how acidic the soil is. pH is one of the m ost important factors regulating soil bacteria growth. For example, wh en soils are very acidic like vinegar, only speciﬁc acid-tolera nt bacteria can live there. Soil grains are very close to each other but also l eave spaces for air and water to enter. The amount of sand, the largest typ e of particle in the soil, tells us how big these soil spaces are. Thi s way, a high sand content means there are big spaces, so that air can ente r the soils easily, but water and nutrients can also drain easily. To study the methanotrophs in our soil samples, we need the genetic information (DNA) of these bacteria [/two.tnum]. First, we obtain all the DNA present in our soil samples, through a process called DNA extraction DNA EXTRACTION Laboratory procedure in which cells are broken open to release the genetic material (DNA) they contain inside, without damaging the DNA. (Figure /one.tnum./three.tnum). This process is done in the laboratory using powerful enzymes that break the cells open without damaging the genetic information. We then analyse the extracted DNA for a speciﬁc region that is present only in methanotrophs. This stretch of DNA is a gene called pmoA. The pmoA gene contains the instructions for the protein that allows methanotrophs to eat atmospheric methane. Knowing the concentration of the pmoA gene in each soil sample tells us how many methanotrophs were living in that sample (Figure /one.tnum./four.tnum). There are several closely related species of methanotrophs that all have s imilar Microbial communities can be described using three properties. Abundance is the total number of bacteria of a certain type present. Richness is the number of diﬀerent kinds of bacteria present in an environment. Community structure describes how many diﬀerent kinds of bacteria there are and how abundant each kind is. DNA information, but diﬀerent species have tiny genetic diﬀeren ces in their DNA, so we can use DNA to identify diﬀerent methanotrophs, like a ﬁngerprint (Figure /one.tnum./five.tnum). Our DNA studies help us to obtain information about the abundance (total number of bacteria of a certain type present), richness (the RICHNESS The number of species (diﬀerent kinds) of organisms present in an environment. number of diﬀerent kinds of bacteria present), and community structure (the diﬀerent kinds of bacteria and the abundance of each COMMUNITY STRUCTURE The combined richness and abundance in the community. kind) of the methanotrophs from each soil sample (Figure /three.tnum). Then, we use mathematics to ﬁgure out which soil or climate conditions are the most important for methanotrophs (Figure /one.tnum./six.tnum).

WHERE THE METHANOTROPHS LIVE

We were not sure if we would ﬁnd methanotrophs in drylands, since these microorganisms need methane to live and drylands are not the typical ecosystem for methane production. So, ﬁnding methanotrophs in all our dryland soil samples was an extraordina ry ﬁnding! We can now say that methanotrophs are widely distributed in global drylands. Surprisingly, we even found some methanotr ophs that are usually found in humid places, such as Denmark, Scotlan d, or New Zealand. We also found that, in drylands, the average annual temperature and aridity are not the main conditions inﬂuencing the abundance and richness of methanotrophs. Abundance and richness may be driven by other factors, such as rainfall. However, climate conditions like mean annual temperature, rainfall, aridity, an d soil properties, such as organic matter, pH, and sand content did aﬀec t the community structure of methanotrophs. For example, higher temperatures increased the abundance of certain methanotrophs that are heat-resistant. In other words, those drylands with higher temperatures, the methanotroph communities may contain more heat-resistant methanotrophs. Climate conditions can also aﬀect s oil properties, for example by favoring the breakdown of rocks, whic h increases sand content, or by modifying soil pH and organic matte r. These soil properties aﬀect the amount of air that can get into the s oil, which we found to be very important for the community structure of the methanotrophs.

WHAT WE LEARNT FROM METHANOTROPHS IN

DRYLANDS? As we found, methanotrophs are abundant and widely distributed in drylands worldwide. Both climate and soil aﬀect the communities of methanotrophs. Moreover, we found the community structure of methane eating bacteria was highly dependent on climate condition s, such as amount of rainfall and temperature, and soil characteri stics as soil organic content. Because we found that climate inﬂuences the methanotrophs, we expect that ongoing climate change will modify methanotroph communities in the coming years, aﬀecting the consumption of atmospheric methane. To date we knew methanotrophs lived on cold and humid places, which will be surely aﬀected by climate change. The vast amount of land that drylands cover and the many methanotrophs they contain may make these areas extremely important for consuming atmospheric methane in the future. In othe r words, dryland bacteria can help us reduce greenhouse gases! T aking good care of drylands now and continue studying the hidden marve ls they contain is important to deal with our future warmer planet. Methane-Eating Bacteria in Drylands can help us!

ORIGINAL SOURCE ARTICLE

Lafuente, A., Bowker, M. A., Delgado-Baquerizo, M., Durán, J., S ingh, B. K., and Maestre, F. T. 2zero.tnum1nine.tnum. Global drivers of methane oxidation and denitrifying gene distribution in drylands. Glob. Ecol. Biogeogr. 2eight.tnum:1two.tnum3zero.tnum–4three.tnum. doi: 1zero.tnum.1one.tnum1one.tnum/geb.1two.tnum9two.tnum/eight.tnum REFERENCES /one.tnum. Cadena, S., Cervantes, F., Falcón, L., and García-Maldonado, J. 2zero.tnum1nine.tnum. The role of microorganisms in the methane cycle. Front. Young Minds /seven.tnum:1three.tnum/three.tnum. doi: 1zero.tnum.3three.tnum8nine.tnum/frym.2zero.tnum1nine.tnum.0zero.tnum1three.tnum/three.tnum /two.tnum. Schallenberg, L., Wood, S., Pochon, X., and Pearman, J. 2zero.tnum2zero.tnum. What can DNA in the environment tell us about an ecosystem? Front. Young Minds /eight.tnum:1five.tnum/zero.tnum. doi: 1zero.tnum.3three.tnum8nine.tnum/frym.2zero.tnum1nine.tnum.0zero.tnum1five.tnum/zero.tnum SUBMITTED: 2seven.tnum April 2zero.tnum2zero.tnum;ACCEPTED: 2zero.tnum May 2zero.tnum2one.tnum; PUBLISHED ONLINE: 1six.tnum June 2zero.tnum2one.tnum. EDITED BY: Rémy Beugnon, German Centre for Integrative Biodiversity Resear ch (iDiv), Germany CITATION: Lafuente A and Cano-Díaz C (2zero.tnum2one.tnum) Can Methane-Eating Bacteriain Drylands Help Us Reduce Greenhouse Gases? Front. Young Minds /nine.tnum:5five.tnum6three.tnum6one.tnum. doi: 1zero.tnum.3three.tnum8nine.tnum/frym.2zero.tnum2one.tnum.5five.tnum6three.tnum6one.tnum CONFLICT OF INTEREST: The authors declare that the research was conducted in the absence of any commercial or ﬁnancial relationships that coul d be construed as a potential conﬂict of interest. COPYRIGHT © 2zero.tnum2one.tnum Lafuente and Cano-Díaz. This is an open-access article distributed under the terms of the Creative Commons Attribution Lic ense (CC BY). The use, distribution or reproduction in other forums is permitted, pr ovided the original author(s) and the copyright owner(s) are credited and t hat the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not compl y with these terms. YOUNG REVIEWER SEBASTIAN, AGE: 1zero.tnum I like sports, reading, math, and animals. AUTHORS ANGELA LAFUENTE I am currently a post-doc at Michigan Technological Universit y, working on carbon cycling in tropical peatlands. I am an ecologist intere sted in understanding how global change aﬀects soil microorganisms and g reenhouse gas ﬂuxes. In my free time, I enjoy the nature going on a hike, cyc ling, or skiing. *[email protected] CONCHA CANO-DÍAZ I am a biologist ﬁnishing my Ph.D. at Universidad Rey Juan Carlos (Spain). My research is focused on the distribution and ecological preferences of so il cyanobacteria. I am currently studying the eﬀects of climate change and soil format ion processes on cyanobacterial communities around the world. I love to make scien tiﬁc illustrations and in my free time I enjoy playing music with the ukulele and singi ng in the choir.