Diversity and Stratification of Archaea in a Hypersaline Microbial Mat

Abstract

The Guerrero Negro (GN) hypersaline microbial mats have become one focus for biogeochemical studies of stratified ecosystems. The GN mats are found beneath several of a series of ponds of increasing salinity that make up a solar saltern fed from Pacific Ocean water pumped from the Laguna Ojo de Liebre near GN, Baja California Sur, Mexico. Molecular surveys of the laminated photosynthetic microbial mat below the fourth pond in the series identified an enormous diversity of bacteria in the mat, but archaea have received little attention. To determine the bulk contribution of archaeal phylotypes to the pond 4 study site, we determined the phylogenetic distribution of archaeal rRNA gene sequences in PCR libraries based on nominally universal primers. The ratios of bacterial/archaeal/eukaryotic rRNA genes, 90%/9%/1%, suggest that the archaeal contribution to the metabolic activities of the mat may be significant. To explore the distribution of archaea in the mat, sequences derived using archaeon-specific PCR primers were surveyed in 10 strata of the 6-cm-thick mat. The diversity of archaea overall was substantial albeit less than the diversity observed previously for bacteria. Archaeal diversity, mainly euryarchaeotes, was highest in the uppermost 2 to 3 mm of the mat and decreased rapidly with depth, where crenarchaeotes dominated. Only 3% of the sequences were specifically related to known organisms including methanogens. While some mat archaeal clades corresponded with known chemical gradients, others did not, which is likely explained by heretofore-unrecognized gradients. Some clades did not segregate by depth in the mat, indicating broad metabolic repertoires, undersampling, or both.Photosynthetic microbial mats occur worldwide and serve as models for microbial community interactions. Fossil microbial mats in the form of stromatolites are one of the earliest distinguishable life forms in the rock record (3.4 billion years) (53) and are often studied to gain insights into the development of life on Earth (3, 11) and the influence that early life may have had on the development of the planet's atmosphere, geosphere, and hydrosphere (20).A large contemporary microbial mat system that has received the attention of microbiological studies is found in the solar saltern operated by the Exportadora de Sal SA in Guerrero Negro (GN), Mexico. The GN saltern, fed from Pacific Ocean seawater pumped from the Laguna Ojo de Liebre, occupies ϳ100 km 2 and consists of ϳ12 precrystallizer ponds with increasing salinity due to evaporation. Many of the ponds in this saltern contain persistent microbial mats. More than a million metric tons of biomass (ϳ17 km 2 by ϳ6 cm by 1.2 gm/cm 3 ) covers the floor of hypersaline pond 4 in the form of a laminated photosynthetic microbial mat that is 4 to 6 cm thick. The subjective, macroscopic appearance of the pond 4 mat is stable from year to year, and the mat has been a subject of numerous microbiological and biogeochemical studies (3,8,15,19,24,29,30,38,47,49,56). Chemical measurements of th...

Microbial Ecology of the Dark Ocean above, at, and below the Seafloor

“…The function of the archaea in these clades is highly speculative. Some reports suggest that some members of the MBGB are heterotrophic methane oxidizers, based on environmental data (for example, see reference 47), while other studies of hypersaline microbial mats hint that the MBGB may be involved in sulfate reduction (469). An exception to this pattern is found in some warmer deep sediments, where members of the Thermococci class are also present (473).…”

“…Further details on methodology are available elsewhere (Toner et al, submitted). For comparison, selected terrestrial and extreme environment habitats, including soils (202), mines (186,476,527), microbial mats (469,475), glacier flows (372), and volcanic and other rock surfaces (215,293), were also included in the analysis as outgroups. It is important to note that some key dark ocean habitats, including abyssal and trench sediments, have not been well analyzed by domain-level 16S rRNA gene clone libraries.…”

Hot Spring Microbial Community Composition, Morphology, and Carbon Fixation: Implications for Interpreting the Ancient Rock Record

“…Woesearchaeota (formerly in the Euryarchaeota DHVEG-6 cluster) (Castelle et al, 2015) OTUs were most abundant in samples from Sites 1 and 2, accounting for 50-75% of the total sequences recovered from these samples ( Figure 3B). Sequences affiliated with Woesearchaeota have been recovered from diverse environments ranging from surface waters of oligotrophic high-altitude lakes (Ortiz-Alvarez and Casamayor, 2016), stratified microbial mats (Saghaï et al, 2017), sediments, plankton and hydrothermal vents (Robertson et al, 2009;Pachiadaki et al, 2011), and hot springs (Kan et al, 2011). A single Woesearchaeota OTU accounted for 45-50% of the sequences recovered from the green and orange mats from Site 1.…”

Molecular Analysis of Bacterial and Circovirus Bioaerosols in Concentrated Animal Feeding Operations

“…One thousand bootstrap trees were cast from the aligned sequence set and the bootstrap scores were annotated onto to the best scoring maximum likelihood tree found with RAxML (Stamatakis 2006). The annotated tree was drawn with Phylovis, as described previously (Robertson et al 2009). …”