souza 2006 4c general

An endangered oasis of aquatic microbial biodiversity in the Chihuahuan desert Valeria Souza* † , Laura Espinosa-Asuar*, Ana E. Escalante*, Luis E. Eguiarte*, Jack Farmer ‡ , Larry Forney § , Lourdes Lloret ¶ , Juan M. Rodrı ´guez-Martı ńez**, Xavier Sobero ń ¶ , Rodol fo Dirzo*, and James J. Elser †† *Departamen to de Ecologı á Evolutiva, Instituto de Ecologı á, Univers idad Naciona l Auto ´ noma de Me ´ xico AP 70-2 75 Coyoaca ´ n, 04510 Mex ico D.F., Mexico; ‡ Department of Geological Sciences, Arizona State University, P.O. Box 871404, Tempe, AZ 85287-1404; § Department of Biological Sciences, University of Idaho, Moscow, ID 83844; ¶ Departamento de Ingenierı á Celular y Biocata ´ lisis, Instituto de Biotecnologıá, Univ ersidad Nacional Auto ´ noma de Me ´ xico AP 510-3 Cuernavaca, Morelos, 62271, Mexico; **Departame nto de Geohidrologı á y Geofı ´sica, Instituto de Ingenierı á Civil, Un iversidad Auto ´ noma de Nuevo Leo ´ n Avenida Fid el Vela ´ squez y Unive rsidad CD Univ ersitaria , 66451 San Nic ola ´ s de los Garza N .L., Mexic o; and †† School of Life Sciences, Arizona State University, Tempe, AZ 85287 Communicate d by Jose ´ Sarukha ´ n, National Autonomous University of Mexico, Mexico D.F., Mexico, February 23, 2006 (received for review September 1, 2005) The Cuatro Cienegas basin in the Chihuahuan desert is a system of springs, streams, and pools. These ecosystems support >70 en- demic species and abundant living stromatolites and other microbial communities, representing a desert oasis of high biodiversity. Here, we combine data from molecular microbiology and geology todocumen t themicrobialbiodiversity of thisuniqueenvironment. Ten watersamples fromlocation s with in theCuatro Cien egas basin and two nei ghborin g val ley s as wel l as thr ee samples of wet sediments were analyzed. The phylogeny of prokaryotic popula- tions in the samples was determined by characterizing cultured organisms and by PCR amplification and sequencing of 16S rRNA genes from total community DNA. The composition of microbial communit ies was also assess ed by dete rmin ing profiles of terminal restriction site polymorphisms of 16S rRNA genes in total community DNA. There were 250 different phylotypes among the 350 cultivated strains. Ninety-eight partial 16S rRNA gene sequences were obtained and classified. The clones represented 38 unique phylo typ es fro m tenmajor lin eag es of Bacteria andone ofArchaea. Unexpectedly, 50% of the phylotypes were most closely related to marine taxa, even though these environments have not been in contact with the ocean for tens of millions of years. Furthermore, terminal restr ictio n site poly mor phis m profiles and geol ogic al data suggest that the aquatic ecosystems of Cuatro Cienegas are hy- dro logi cally inter connectedwith adjac ent valle ys recen tly targ eted for agricultural intensification. The findings underscore the conservation value of desert aquatic ecosystems and the urgent need for study and preservation of freshwater microbial communities. Cuatro Cienegas terminal restriction site polymorphism 16S clone library water conservation microbial ecology C onservation efforts often focus on landscapes of scenic value or habitats with endangered or charismatic animals and plants. Howeve r, ecosystems also harbor a my riad of microor ganisms that not onl y pla y a cri tic al rol e in ecos yste m functi oningbut als o contain a remarkable reco rd of thei r evo lut ion ary his tory within the ir genomes. Freshwater aquatic ecosystems face increasing anthro- pogenic pressures worldwide (1–4), especially in arid regions (5–7), where we risk losing unique aquatic habitats without even knowing the nature and extent of their biodiversity. Here we report findings regarding microbial biodiversity in an endangered desert aquatic ecosyst em in Mexico [the Cua tro Cie nega s bas in (CCB )] ind ica ting that the composition of modern microbial assemblages may reflect their distant geological past and that there is significant subsurface interconnection of the ecosystems in adjace nt sedimentary basins . Understanding the spatial and evolutionary relationships of the mi cr obi ota of the CCB is re ga rde d as a cr it ical st ep tow ar d imp lementing an effecti ve cons ervat ion str ategy to protect the ecosyste ms found there. The CCB is in central Mexico, in the state of Coahuila and is a valley measuring 30 km by 40 km located at 740 m above sea level and surrounded by high mountains (3,000 m). The CCB is an enclosed evaporitic basin that receives 150 mm of annual precipitation. Despite the arid climate, the CCB harbors an ext ens ive system of springs, streams, and poo ls of sig nific ant scientific interest (8). Documented biodiversity includes 70 en- demic species of aquatic vertebrates, distributed among a wide variety of aquatic and terrestrial ecosystems. Other remarkable featu res of the aquat ic ecosystems inclu de the living stromatoli tes and other microbial communities that form the basis of complex food webs (8–11). From this perspective, CCB is widely regarded as a biodiversity oasis within the Chihuahuan desert. Although there is ample evidence that prokaryotes form the basis of food webs in this unique setting, we still know very little about the microbial diversity of these ecosystems. Given the high levels of end emi sm and biodiv ers ity of higher organis ms at the site, an 85,000-ha area is currently designated as a federal ‘‘Area for the Protection of Flora and Fauna’’ (12). Such a designation concep- tually accommodates conservation of natural systems alongside sustain able develo pment activiti es. The World Wildli fe Federa tion, Mexico’s National Commissio n on Biodi versity (CONABIO), and nongove rnment organizations, such as PRONATURA and the Nature Conservancy, have all classified the Cuatro Cienegas valley as globally outstanding because of its high species endemism and recent history of evolutionary radiations. The high mountains surrounding the CCB expose upper Jurassic to lower Cretaceo us lime stone s, sulfa te-rich evaporites,sandstones, and conglomerates of the San Marcos and Cupido formations (8, 13) (Fig. 3, which is published as supporting information on the PNA S web sit e). Div erse surfa ce hab itat s, inc lud ing mar she s, ponds, springheads, spring-fed streams, and playa lakes are inter- connected with subsurface caverns, sinkholes, and other limestone and evaporite karst features (10). Between locations, environmen- tal conditions can differ dramatical ly in water chemistry, f low rate, and size volume of spring discharge (10, 14). Radiocarbon dating of sediment core s take n from poo ls indicatesthat some hav e exist ed for thousands of years, perhaps as long as 31,000 (15). Older travertine hot-spring deposits and lower-temperature tufa mounds are found in association with some active springs but also occur in the older, dry portion s of the basin f loor, sugge sting the long-term persis tence of aqua tic habitats in the basin (10). Although prelim- inary models have been proposed (16), the hydrology of the region Conflict of interest statement: No conflicts declared. Abbre viations:CCB, Cuatr o Cien egasbasin;T-RFLP,termina l restriction sitepolymor phism. Datadeposi tion:Thesequenc esreportedin thispaperhavebeen depos itedin theGenBank database (accession nos. AY604936 –AY604973). † To whom correspondence should be addressed. E-mail: [email protected]. Present add ress: Centr o de Ciencias Geno ´ micas, Uni versidad Na cional Auto ´ noma de Me ´ x- ico, Cuernavaca, Morelos, 62210, Mexico. © 2005 by The National Academy of Sciences of the USA www.pnas.orgcgidoi10.1073pnas.0601434103 PNAS April 25, 2006 vol. 103 no. 17 6565–6570 E C O L O G Y

souza 2006 4c general

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