Microbialites are rock-like underwater structures that look like reefs but are made entirely of millions of microbes. These structures are very ancient and can be found in di􀀀erent environments on every continent on Earth. Mexico has many
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  BIODIVERSITY Published:  September doi: ./frym.. MICROBIALITES:WHATONEARTH?  Alfredo Yanez-Montalvo  ,  , Bernardo Águila    , Elizabeth S. Gómez-Acata    , Yislem Beltrán    , PatriciaM. Valdespino-Castillo    , Carla M. Centeno    and Luisa I. Falcón  *    Instituto de Ecología, Universidad Nacional Autónoma de México, Mérida, Mexico   El Colegio de la Frontera Sur, Chetumal, Mexico   Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, Puerto Morelos, Mexico   Lawrence Berkeley National Laboratory, Berkeley, CA, United States YOUNG REVIEWERS: DANA AGE:  MARÍAJOSE AGE:  MARIANA AGE:  Microbialites are rock-like underwater structures that look like reefsbut are made entirely of millions of microbes. These structuresare very ancient and can be found in different environments onevery continent on Earth. Mexico has many microbialite reefs,in desert valleys, crater-lakes, and coastal lagoons. Science helpsus to understand the microbes that build microbialites, to knowwhether the same kinds of microbes make up microbialites indifferent regions of the world, and to figure out how the microbesorganize into microbialites. Many things are damaging microbialitesin Mexico, including poorly planned development, pollution fromlack of sewage treatment, too much water usage, and the fertilizersused for agriculture. Policies that regulate development are urgentlyneeded to help save these diverse and ancient microbial reefs.  September  | Volume  | Article  |    Yanez-Montalvo et al. What are Microbialites? WHATAREMICROBIALITES? Do you know what a  microbialite  is? Not many people do. This is MICROBIALITE A rock-like structuremade by millions ofmicrobes thatprecipitate carbonate. because microbialites look like slimy underwater rocks, but they areactually reefs made up of  microbes  (simple, one-celled organisms). MICROBE An organism that isseen underthe microscope. Microbialites are fascinating, because these rock-like structures aremade by the interaction of millions of microbes that live in certainaquatic environments. The microbes facilitate the precipitation ofminerals from the water, to form the microbialite structure [].Since microbialites are like rocks, they have remained on earthsince extremely ancient times. Fossilized microbialites, known as stromatolites  (from the Greek  strõma,  meaning bed or layer, and STROMATOLITE Fossilized microbialites,and are the oldestfossils dated so far. lithos,  meaning rock), are the oldest evidence of life on Earth, datingback to . billion years ago []. Cyanobacteria  are one type of microbe found in microbialites, and CYANOBACTERIA A phylum of bacteriathat canmake photosynthesis. these bacteria do all kinds of important work. Cyanobacteria buildshelters that protect the microbial community from dangerous thingsin the environment, including protecting them from drying out andfrom damage by the sun’s UV rays. The shelters built by cyanobacteriatrap and bind sediments and minerals, which help to grow themicrobialites [, ]. Cyanobacteria are also involved in producingslimy substances called  exopolymeric substances (EPS) , which are EXOPOLYMERICSUBSTANCES (EPS) Mucous-like moleculesreleased bymicroorganisms intotheir environment,which help themicrobes remain closetogether andcommunicate witheach other. like mucous. Exopolymeric substances help microbes to stay closeto each other and allow the cells to communicate with each other[]. Cyanobacteria also have pigments that interact with photonsfrom the Sun, allowing them to perform photosynthesis, which leadsto the incorporation of carbon from the atmosphere (in the formof CO  ) into their cells. Cyanobacteria take up water and produceoxygen during photosynthesis. Since microbialites are so old, theyprobablyparticipatedinoxygenatingtheearlyEarth.Gentlyandslowly,bubble by bubble, microbialites produced oxygen, and by ∼ . billionyears ago, the chemistry of earth’s atmosphere had changed enoughto support the evolution of other life forms []. Cyanobacteria areone of the food sources for other kinds of microbes, helping manydifferent kinds of microbes work together as a unit to form themicrobialite community. WHEREDOMICROBIALITESLIVE? There are living microbialites in different aquatic environments allover the globe, including polar, temperate, and tropical locations.In Mexico, there are microbialite communities in different locations,includingcoastallagoons,crater-lakes,anddesertponds(Figure).  AREALLMICROBIALITESINMEXICOTHESAME? In our study, we wanted to understand if microbialites from differentlocations in Mexico are similar or different, in terms of the microbes  September  | Volume  | Article  |    Yanez-Montalvo et al. What are Microbialites? Figure  Figure  Microbialitereeflocationsin Mexico that wereexamined in our study:Cuatro Ciénegas basinin Northern México,crater-lake Alchichicain Central México, andBacalar lagoon in theYucatán Península. that make them up. To study this, we explored various sites usingcatamarans, kayaks, and boats. Once we identified microbialite reefs,we took small samples ( ∼ g) of microbialites from the first fewmillimeters of their surface, using clean, microbe-free tools andcontainers. We stored these samples in coolers and then froze themwhen we got back to the laboratory. Later, we extracted the DNAfrom these microbialite samples, using different enzymes, soaps,and organic molecules. To study this DNA, we first amplified itusing a technique known as  polymerase chain reaction (PCR)  and POLYMERASECHAIN REACTION(PCR) A laboratory techniquefor obtaining millions ofcopies of pieces ofDNA, so that they canbe moreeasily analyzed. analyzed how similar or different the microbial DNA sequences wereto each other.By comparing certain regions of the microbial DNA, thousands ofmicrobes can be identified from a pea-sized rocky sample!We found that all the microbialite communities we studied hadthe same groups of microbes, just in slightly different proportions(Figure ) []. The main microbes in microbialites are Cyanobacteria(which we already discussed), Proteobacteria and Bacteroidetes  September  | Volume  | Article  |    Yanez-Montalvo et al. What are Microbialites? Figure  Figure  Several different kindsof bacteria make up themicrobialites found invarious regions ofMexico. The types ofbacteria are listed onthe left, and the piecharts under thepictures of themicrobialites show thatmicrobialites from eachlocation are made upof different proportionsof these same typesof bacteria. (which are very diverse and can digest many types of substrates,including carbon, nitrogen, and sulfur), Chloroflexi (which can do atype of photosynthesis that does not produce oxygen, but insteadproducesasubstancecalledsulfide),andArchaea(whichcanproduceand eat methane) (Figure ).Proteobacteria are the most diverse bacteria in microbialites,making up –% of the total diversity in these structures,followed by a group of bacteria that we know very little aboutand are called unclassified bacteria, which make  ∼ % of thebacteria in microbialites. Other bacteria, including Bacteroidetes,Plactomycetes, Verrucomicrobia, Chloroflexi, and Cyanobacteriacomprise the remaining diversity (Figure ). The microbes inmicrobialites have been interacting amongst themselves and with theenvironmentformanymillionsofyears,andhavehelpedtransformtheEarth, making our life on this planet possible through the productionof oxygen and other important processes. Microbial communitieslike the ones that form microbialites help the Earth to functionas a unit.  AREMICROBIALITESINMEXICODOINGWELL? Since microbialites are self-sufficient, they only need clean water,sunlight, and gases from the atmosphere to grow and develop. Allthe microbialites we have studied in Mexico live in places with cleanand clear water, and we have found massive microbialite formationsthat have been dated to be  ∼ , years of age []. Some ofthe beautiful aquatic environments where microbialites have thrivedfor thousands of years have warm, clear, tropical waters. This isthe case for a coastal lagoon called Bacalar in southern Mexico,which has attracted loads of tourists. But a problem arises whenthere is no infrastructure to treat the sewage from the growingpopulation, leading to pollution of the lagoon. Microbialites in Bacalarlagoon and in other areas of Mexico are being threatened by humanactivities. In northern Mexico, the microbialites that thrive in the  September  | Volume  | Article  |    Yanez-Montalvo et al. What are Microbialites? Figure  Figure  Many microbes buildmicrobialites. They dophotosynthesis, andcapture CO  ,producing oxygen andare active in thenitrogen, sulfur andmethane cycles. Cuatro Cienegas valley, which has many ponds in the middle of adesert, are at risk because too much water is being removed fromthe ponds for agriculture. In central Mexico, microbialites that livein crater-lakes are also at risk, due to both pollution and too muchwater usage.Humans are the main problem for the world’s biodiversity, but weare also the solution. Microbialites are part of Earth’s history and itis wonderful that we can observe these ancient communities today!We have the responsibility to be educated about our environment andto make intelligent choices. Let us use efficient water treatment andtechnology to save microbialites and other aquatic life! Before goingon a holiday, read about the places you will visit and learn about theplants, animals, and bacteria that live there, so that you can enjoy theircompany without harming them or their environment.  AUTHORCONTRIBUTIONS The authors contributed equally to writing this paper. ORIGINALSOURCEARTICLE Valdespino-Castillo, P. M., Hu, P., Merino-Ibarra, M., López-Gómez, L.M., Cerqueda-García, D., González-De Zayas, R., et al. . Exploringbiogeochemistry and microbial diversity of extant microbialites inMexico and Cuba.  Front. Microbiol.  :. doi: ./fmicb..  September  | Volume  | Article  |  
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