Methane cycling in the Salton Sea mud pots.
The Davis-Schrimpf seep field lies southeast of the Salton Sea, at the northernmost end of the East Pacific Rise. It's accessible by road. The field has a fantastic array of mud pots, mud volcanoes, gas fissures, and saline pools. In some ways, it's a terrestrial version of a deep sea hydrothermal vent! Gases, mostly carbon dioxide, escape from the subsurface through mud of variable salinity and viscosity. Fluids range from cool to hot (over 65 Celsius). The mud volcanoes are hot, with essentially fresh water inputs. Mud pots and pools are much cooler, with salinities that range from about 5% to over 15%. Some of the pots have elevated levels of different metals including iron and manganese, adding yet another layer of pot-to-pot geochemical variability. Carbon dioxide and steam in the region are used commercially (background, below).
The pools range in color from clear, rimmed in green and yellow, to red and muddy. Photosynthesis is occurring in some, but not all, of the pools. Many pools have an associated gryphon (a mud volcano less than 3 meters in height).
Areas of active bubbling occur throughout the field. The gases in these bubbles are rich in carbon dioxide. Occasionally, methane is also present in significant levels. Some of the seeps have the characteristic stench of hydrogen sulfide.
We're interested in asking how microorganisms evolve and adapt to this wide array of conditions. We're specifically interested in whether methane cycling in these pots is similar to processes at deep sea vents, or if it is uniquely adapted to this sunlit, intermittently wetted landscape. . We are interested in part because methane escaping these features will directly enter the atmosphere; there is no overlying marine water column to act as a methane biofilter.
We've recently found that microbial populations in these pools vary as much as the pools themselves (major taxa in five pools, shown below left. These taxa include Sulfurimonas, Marinobacter, Halothiobacillus, and members of Rhodobacteriaceae.) Danielle Fradet, a student working with Patricia in 2015, cultured a new methanotroph (genus Methylomarinum, middle and right images) from a particularly 'muddy pot.' This vigorously motile organism is most abundant in a pot with elevated metals. We've demonstrated that the genome of Methylomarinum encodes more metal efflux transporters than other methanotrophic genomes sequenced to date, and that the new isolate tolerates substantially elevated metal concentrations in culture. We hypothesize that this genus can outcompete other methanotrophic genera in metal-rich niches.
We've recently found that microbial populations in these pools vary as much as the pools themselves (major taxa in five pools, shown below left. These taxa include Sulfurimonas, Marinobacter, Halothiobacillus, and members of Rhodobacteriaceae.) Danielle Fradet, a student working with Patricia in 2015, cultured a new methanotroph (genus Methylomarinum, middle and right images) from a particularly 'muddy pot.' This vigorously motile organism is most abundant in a pot with elevated metals. We've demonstrated that the genome of Methylomarinum encodes more metal efflux transporters than other methanotrophic genomes sequenced to date, and that the new isolate tolerates substantially elevated metal concentrations in culture. We hypothesize that this genus can outcompete other methanotrophic genera in metal-rich niches.
Fradet 2016 reported a physical association between this member of Methylomarinum and a member of Methylophaga, a non-methanotrophic methylotroph. This association suggests an ecological relationship between these organisms. Recent high-throughput sequencing data supports the idea. Methylomarinum and Methylophaga are the dominant members of their respective guilds in the mud pot; each accounting for approximately 2.5% of the total community.
Current and future directions.
* The microbial population in our 'muddy pot' is similar to populations in the deep brine pools of the Red Sea. Understanding the physical or chemical basis of these similarities is an area of active research.
* We'd like to characterize the newly isolated Methylomarinum species, and compare its physiology to that of the type species of the genus, M. vadi. M. vadi was isolated from the seafloor in Japan. Understanding the comparative behaviors of these two species may give insights into adaptations specific to the deep sea and land-based saline pots.
* Future work includes thorough assessment of how geochemical features including salinity, metal content, and temperature drive microbial populations.
* Archaeal Halobacteriaceae account for up to 10% of the total microbial communities in the saline pools. Archaeoglobus comprises up to 5% of the microbial community in the hotter gryphons. These and other archaea will be a part of the story, as it develops.
* We'd like to characterize the newly isolated Methylomarinum species, and compare its physiology to that of the type species of the genus, M. vadi. M. vadi was isolated from the seafloor in Japan. Understanding the comparative behaviors of these two species may give insights into adaptations specific to the deep sea and land-based saline pots.
* Future work includes thorough assessment of how geochemical features including salinity, metal content, and temperature drive microbial populations.
* Archaeal Halobacteriaceae account for up to 10% of the total microbial communities in the saline pools. Archaeoglobus comprises up to 5% of the microbial community in the hotter gryphons. These and other archaea will be a part of the story, as it develops.