PROJECTS |
Genome and transcriptomic profiling of the polyextremophilic yeast Naganishia friedmannii exposed to freeze-thaw stress
Naganishia friedmannii is an extremely stress tolerant basidiomycete yeast that has been proposed as a model organism for exobiology and studies on stress resistance in eukaryotes. This yeast is very abundant in some of the most extreme environments of the Earth’s cryosphere and its survival limits have been investigated in several studies demonstrating its high tolerance of UV-B and UV-C radiation, extreme temperature fluctuations, desiccation and exposure to the stratosphere. This polyextremophilic yeast is the most abundant microeukaryote of high elevation volcanoes of the Atacama region and we have successfully isolated and cultured it from soils collected from > 5000 m elevation on Volcán Llullaillaco, Chile. Our studies have shown that N. friedmannii can grow relatively rapidly in pure culture during freeze–thaw cycles and that it increases in relative abundance in soils subjected to freeze–thaw cycles both in its natural environment and in laboratory when water and nutrients are available. Among the multiple environmental stressors that N. friedmannii has to cope with, extreme thermal fluctuation is possibly one of the most relevant and least studied. Mechanisms underpinning tolerance to extreme thermal stress have been virtually unexplored and efforts in our lab are currently ongoing to get a better understanding on strategies employed by N. friedmannii. We are growing N. friedmannii in a temperature-controlled chamber mimicking environmental temperature fluctuations cycling up to a high of 27°C during the day and a low of -10°C at night with an amplitude of 37°C in 24 hours. We will extract total RNA at different temperatures within the daily temperature cycle to define its transcriptional response when subjected to extreme thermal stress. Global warming and climate change are increasingly exposing life on Earth to temperature fluctuations: it is therefore imperative to explore the molecular pathways that have evolved in organisms such as N. friedmannii that are able to cope with and reproduce under thermal stress. These comparisons will shed light on hypotheses concerning the main pathways involved into thermal stress response in this yeast and elucidate the molecular mechanisms underpinning thermal tolerance. We expect that such studies will provide important insights into the molecular nature of thermal stress response in one of the most abundant microeukaryotes of the cryosphere. |
Microbial succession patterns in a recently deglaciated area of the Antarctic peninsula
Understanding successional patterns of organisms over space and time has been a long-standing research topic in ecology. Now it is more important than ever, as accelerating glacier recession is a phenomenon that is affecting most of polar and high elevation areas worldwide. The Antarctic peninsula has been strongly affected by rapid warming in the last few decades, driving the expansion of deglaciated areas. 87% of glaciers along the west coast of the Antarctic peninsula have receded over the last half century, a trend which is expected to continue. We examined a soil chronosequence of a glacier forefield located next to the US Antarctic Palmer Station that can be considered a model ecosystem for glaciers in the rapidly warming Antarctic peninsula. Based on satellite and aerial images and observations by Palmer Station personnel, this area appears to have started becoming ice-free around 1963 and we estimate that the glacier has retreated on average of 10m year-1 since this time. This project addresses hypotheses regarding the relationship between microbial community assembly, environmental parameters, and ecosystem functioning following glacial retreat. Our main objectives are to contrast bacterial and eukaryotic successional dynamics and community assembly as well as elucidate the most important environmental drivers of microbial trajectories. |
Microbial life and biogeography of the disappearing periglacial ecosystem at the top of Mt. Kilimanjaro
High mountains are perfect environments to study biogeography because they are essentially "islands of the cryosphere" surrounded by more temperate habitats. Kilimanjaro is Africa’s highest mountain and the tallest free-standing mountain on Earth. In recent years Kilimanjaro and its dramatic ice loss have become an “icon” of climate change, attracting broad interest in its fate. The three remaining ice fields on the plateau and slopes are shrinking laterally and rapidly thinning leaving behind just the ragged fringe of an ice cap, which is believed to have once covered the entire summit of the mountain. As the glaciers on top of Kilimanjaro continue to recede, unique microbial communities will be gradually compromised and lost. Its high elevation and considerable isolation from any other mountain range also makes it an ideal site to further advance our knowledge of microbial endemicity and biogeographic patterns. Our studies have so far shown that the summit of Mt. Kilimanjaro harbors unexpectedly diverse and rich assemblages of Bacteria and Eukarya indicating that there may be high rates of dispersal to the top of this tropical mountain. The combination of cosmopolitan bacterial diversity and weak biogeographical patterns suggest that the effect of distance and local environmental conditions is overwhelmed by continuous dispersal. On the other hand, eukaryotic communities showed more evidence of dispersal limitations and apparent endemism. Taken together, our study suggests that the ecosystem atop Mt. Kilimanjaro supports both cosmopolitans and endemic microbial communities. These results argue for more intense study of this unique high-elevation “island of the cryosphere” before the glaciers of Kilimanjaro disappear forever. |
Microbial diversity and functioning at extreme elevations on Atacama volcanoes
Soils on the world’s highest volcanoes in the Atacama region represent some of the harshest ecosystems yet discovered on Earth. Life in these environments must cope with high UV flux, extreme diurnal freeze–thaw cycles, low atmospheric pressure, sparse and intermittent water availability, and extremely low nutrient content. These volcanoes contain microbial communities of extremely low diversity, except in areas near fumaroles and pinnacle-shaped ice structures known as penitentes, which represent intermittent water sources. Our interest lies on how extremophiles cope with the dramatic environmental stresses encountered in these environments and which microorganisms are functioning in situ. Our studies on two of these volcanoes, Volcán Socompa and Llullaillaco, have surveyed microbial diversity across several different niches, from hyperarid soils to intermittent oases where water is transiently available. Fertilization experiments and soil microcosm manipulations studies have shed light on which fraction of the detected microbial community of this extreme landscape can become active when water and nutrients limitations are alleviated. Future work will include resampling of field fertilization plots to investigate how nutrient additions have impacted the inhabiting microbial community in the long term. Some of our most recent research revealed how nieves penitentes found at high elevations on Volcán Llullaillaco represent a new habitat for snow algae in one of the most extreme environments on Earth. Algae in the genera Chlamydomonas and Chloromonas are dominant, both of which are closely related to known snow algae from alpine and polar environments. In this environment penitentes provide both water and shelter from harsh winds and high UV radiation. Intriguingly, recent planetary investigations have suggested the existence of penitente-like structures on other planetary bodies of our solar system. Therefore, penitentes and the harsh environment that surrounds them provide a new terrestrial analog for astrobiological studies of life beyond Earth. |
Microbial community assembly in cryoconite holes and nearby environments
Cryoconite holes are water-filled holes that form on glacier surfaces because of enhanced glacial melting around trapped sediment. Antarctic cryoconite holes represent uniquely tractable systems for studying microbial community assembly processes and patterns because they typically form an ice lid that can isolate them from the atmosphere for years. Our project on cryoconite on glaciers of the McMurdo Taylor Valley aims to investigate the degree to which stochastic processes guide microbial community assembly. We have also been constructing new cryoconite holes to experimentally alter microbial assembly order and community size to shed light on priority effects. Biogeographic surveys of the Taylor Valley further aim to establish potential sources for the sediments that form cryoconite holes and microcosm manipulations of supraglacial sediments with nitrogen and phosphorus addition investigate the role of nutrient boosting in these ecosystems. |