Complexity in Natural Microbial Ecosystems: The Guerrero Negro Experience

Abstract

The goal of this project is to describe and understand the organismal composition, structure, and physiology of microbial ecosystems from hypersaline environments. One collection of such ecosystems occurs at North America's largest saltworks, the Exportadora de Sal, in Guerrero Negro, Baja California Sur. There, seawater flows through a series of evaporative basins with an increase in salinity until saturation is reached and halite crystallization begins. Several of these ponds are lined with thick (10 cm) microbial mats that have received some biological study. To determine the nature and extent of diversity of the microbial organisms that constitute these ecosystems, we are conducting a phylogenetic analysis using molecular approaches, based on cloning and sequencing of small subunit (SSU) rRNA genes (16S for Bacteria and Archaea, 18S for Eukarya). In addition, we report preliminary results on the microbial composition of a laminated community that occurs in a crystallized gypsum-halite matrix in near-saturated salt water. Exposure of the interior of these large (kilogram) wet, endoevaporite crystals reveals a multitude of colors: layers of yellow, green, pink, and purple microbiota. To date, analyses of these two environments indicate the ubiquitous dominance of uncultured organisms of phylogenetic kinds not generally thought to be associated with hypersaline environments.

Community Composition of a Hypersaline Endoevaporitic Microbial Mat

“…In a molecular study of anoxic sediments below a gypsum encrusted community in Salin-de-Giraud, France, the most abundant groups were the Bacteroidetes, Firmicutes, and ␣-, ␥-, and ␦-proteobacteria (41). Finally, in a 16S rRNA survey of endoevaporitic microbial communities in the salterns of Guerrero Negro, Spear et al (66) found a predominance of bacterial phylotypes affiliated with Cyanobacteria, Bacteroidetes, ␣-, ␥-, and ␦-proteobacteria, Planctomycetes, and Firmicutes. Green sulfur bacteria and ε-proteobacteria were also detected but in low numbers.…”

“…15%, the photosynthetic communities tend to form compact and highly active microbial mats on the surface of the pond floor, whereas in ponds containing between 15 and 25% salt, the mats are less compact since the photosynthetic layers tend to be embedded within the crystalline salt crust on the pond bottom. Such endoevaporitic gypsum-or halite-associated microbial systems have been reported from a number of solar salterns around the world, including those from the coasts of the Gulf of Mexico (55,66), the Mediterranean Sea (12), the Baja Peninsula (60), and the Red Sea (53). In endoevaporitic microbial ecosystems associated with gypsum deposits, several layers of oxygenic and anoxygenic phototrophs are often visible, indicating some level of stratification in the populations.…”

Micron-scale mapping of sulfur cycling across the oxycline of a cyanobacterial mat: a paired nanoSIMS and CARD-FISH approach

“…Previous work has shown that sulfur-cycling organisms form a major metabolic and phylogenetic component of microbial mats in Guerrero Negro and similar environments (Canfield and Des Marais, 1993;Jorgensen, 1994;Risatti et al, 1994;Krekeler et al, 1997;Teske et al, 1998;Minz et al, 1999a,b;Spear et al, 2003;Sorensen et al, 2005;Ley et al, 2006). Whole-cell FISH surveys of microbial assemblages within the mat, focusing on sulfate reducers and other known monophyletic sulfur-metabolizing guilds, allow for micron-scale mapping of the spatial distribution of these organisms (for example, Minz et al, 1999a;Wieland et al, 2003;Tonolla et al, 2005;Baumgartner et al, 2006).…”

“…Previous studies of these mats have characterized the bulk microbiological community structure (Risatti et al, 1994;Spear et al, 2003;Ley et al, 2006), large-scale sulfur cycling (Canfield and Des Marais, 1993;Jorgensen, 1994) and daily variations in response to the periodic redox forcing from photosynthesis (Jorgensen, 1994;Visscher et al, 2003;Decker et al, 2005). Microcoleus-dominated mats also support active sulfate reduction by aerotolerant sulfate reducers (Teske et al, 1998) in the photosynthetically active uppermost few millimeters (Canfield and Des Marais, 1993).…”

[FeFe] Hydrogenase Genetic Diversity Provides Insight into Molecular Adaptation in a Saline Microbial Mat Community

“…Little is known concerning the potential role of fermentative bacteria and/or H 2 cycling in phototrophic microbial mat systems, such as the 6-cm-thick and extremely diverse microbial mats inhabiting the saline ponds at the Exportadora de Sal SA saltern in Guerrero Negro (GN), Baja California Sur, Mexico. Recent 16S rRNA gene surveys in GN revealed an abundance of bacteria in the upper 2 mm of the mat that, based on their phylogenetic affiliation, are thought to harbor fermentative metabolisms (6,8,13,16,20,28). Similarly, previous studies have shown that the flux of H 2 from the surface of the phototrophic mats present in GN is ϳ150-fold higher during the night than during the day (9).…”