Elaina Hancock – UConn Communications

Much of life on planet Earth today relies on oxygen to exist, but before oxygen was present on our blue planet, lifeforms likely used arsenic instead. These findings are detailed in research published today in Communications Earth and Environment.

A key component of the oxygen cycle is where plants and some types of bacteria essentially take sunlight, water, and CO2, and convert them to carbohydrates and oxygen, which are then cycled and used by other organisms that breathe oxygen. This oxygen serves as a vehicle for electrons, gaining and donating electrons as it powers through the metabolic processes. However, for half of the time life has existed on Earth, there was no oxygen present, and for the first 1.5 billion years, we really don’t how these systems worked, says lead author of the study and UConn Professor of Marine Sciences and Geosciences Pieter Visscher.

Light-driven, photosynthetic organisms appear in the fossil record as layered carbonate rocks called stromatolites dating to around 3.7 billion years ago, says Visscher. Stromatolite mats are deposited over the eons by microbial ecosystems, with each layer holding clues about life at that time. There are contemporary examples of microbes that photosynthesize in the absence of oxygen using a variety of elements to complete the process, however it’s unclear how this happened in the earliest life forms.

Theories as to how life’s processes functioned in the absence of oxygen have mostly relied on hydrogen, sulfur, or iron as the elements that ferried electrons around to fulfill the metabolic needs of organisms.

As Visscher explains, these theories are contested; for example, photosynthesis is possible with iron, but researchers do not find evidence of that in the fossil record before oxygen appeared some 2.4 billion years ago. Hydrogen is mentioned, yet the energetics and competition for hydrogen between different microbes shows it is highly unfeasible.

Arsenic is another theoretical possibility, and evidence for that was found in 2008. Visscher says the link with arsenic was strengthened in 2014 when he and colleagues found evidence of arsenic-based photosynthesis in deep time. To further support their theory, the researchers needed to find a modern analog to study the biogeochemistry and element cycling.

Finding an analog to the conditions on early Earth is a challenge for a number of reasons, besides the fact that oxygen is now abundant. For instance, the evidence shows early microbes captured atmospheric carbon and produced organic matter at a time when volcanic eruptions were frequent, UV light was intense in the absence of the ozone layer, and oceans were essentially a toxic soup.

Another challenging aspect of working within the fossil record, especially those as ancient as some stromatolites, is that there are few left due to the cycling of rock as continents move. However, a breakthrough happened when the team discovered an active microbial mat, currently existing in the harsh conditions in Laguna La Brava in the Atacama Desert in Chile.

The mats have not been studied previously but present an otherworldly set of conditions, like those of early Earth. The mats are in a unique environment which leaves them in a permanent oxygen-free state at high altitude where they are exposed to wild, daily temperature swings, and high UV conditions. The mats serve as powerful and informative tools for truly understanding life in the conditions of early Earth.

Visscher explains, “We started working in Chile, where I found a blood red river. The red sediments are made up by anoxogenic photosynthetic bacteria. The water is very high in arsenic as well. The water that flows over the mats contains hydrogen sulfide that is volcanic in origin and it flows very rapidly over these mats. There is absolutely no oxygen.”

The team also showed that the mats were making carbonate deposits and creating a new generation of stromatolites. The carbonate materials also showed evidence for arsenic cycling – that arsenic is serving as a vehicle for electrons — proving that the microbes are actively metabolizing arsenic, much like oxygen in modern systems. Visscher says these findings, along with the fossil evidence, gives a strong sense of the early conditions of Earth.

“Arsenic-based life has been a question in terms of, does it have biological role or is it just a toxic compound?” says Visscher.

That question appears to be answered: “I have been working with microbial mats for about 35 years or so. This is the only system on Earth where I could find a microbial mat that worked absolutely in the absence of oxygen.”

Visscher points out that an important tool they used to perform this research is similar to one onboard the Mars Perseverance rover, currently en route to Mars.

“In looking for evidence of life on Mars, they will be looking at iron and probably they should be looking at arsenic also.”

This work was supported by grants from NSF grant OCE 1561173, ISITE project UB18016-BGS-IS and the São Paulo Research Foundation FAPESP, grant 2015/16235-2. You can also find out more about this work in The Conversation.

By Elaina Hancock.

As humans continue to send large quantities of carbon into the atmosphere, much of that carbon is absorbed by the ocean, and UConn researchers have found high CO2 concentrations in water can make fish grow smaller.

Researchers Christopher Murray PhD ’19, now at the University of Washington, and UConn Associate Professor of Marine Sciences Hannes Baumann have published their findings in the Public Library of Science (PLoS One).
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0235817

“The ocean takes up quite a bit of CO2. Estimates are that it takes up about one-third to one-half of all CO2 emissions to date,” says Murray. “It does a fantastic job of buffering the atmosphere but the consequence is ocean acidification.”

Life relies on chemical reactions and even a slight change in pH can impede the normal physiological functions of some marine organisms; therefore, the ocean’s buffering effect may be good for land-dwellers, but not so good for ocean inhabitants.

Baumann explains that in the study of ocean acidification (or OA), researchers have tended to assume fish are too mobile and tolerant of heightened CO2 levels to be adversely impacted.

“Fish are really active, robust animals with fantastic acid/base regulatory capacity,” says Murray. “So when OA was emerging as a major ocean stressor, the assumption was that fish are going to be OK, [since] they are not like bivalves or sea urchins or some of the other animals showing early sensitivities.”

The research needed for drawing such conclusions requires long-term studies that measure potential differences between test conditions. With fish, this is no easy task, says Baumann, largely due to logistical difficulties in rearing fish in laboratory settings.

“For instance, many previous experiments may not have seen the adverse effects on fish growth, because they incidentally have given fish larvae too much food. This is often done to keep these fragile little larvae alive, but the problem is that fish may eat their way out of trouble — they overcompensate – so you come away from your experiment thinking that fish growth is no different under future ocean conditions,” says Baumann.

In other words, if fish are consuming more calories because their bodies are working harder to cope with stressors like high CO2 levels, a large food ration would mask any growth deficits.

Additionally, previous studies that concluded fish are not impacted by high CO2 levels involved long-lived species of commercial interest. Baumann and Murray overcame this hurdle by using a small, shorter-lived fish called the Atlantic silverside so they could study the fish across its life cycle. They conducted several independent experiments over the course of three years. The fish were reared under controlled conditions from the moment the eggs were fertilized until they were about 4 months old to see if there were cumulative effects of living in higher CO2 conditions.

Murray explains, “We tested two CO2 levels, present-day levels and the maximum level of CO2 we would see in the ocean in 300 years under a worst-case emissions scenario. The caveat to that is that silversides spawn and develop as larvae and early juveniles in coastal systems that are prone to biochemical swings in CO2 and therefore the fish are well-adapted to these swings.”

The maximum CO2 level applied in the experiments is one aspect that makes this research novel, says Murray,

“That is another important difference between our study and other studies that focus on long-term effects; almost all studies to date have used a lower CO2 level that corresponds with predictions for the global ocean at the end of this century, while we applied this maximum level. So it is not surprising that other studies that used longer-lived animals during relatively short durations have not really found any effects. We used levels that are relevant for the environment where our experimental species actually occurs.”

Baumann and Murray hypothesized that there would be small, yet cumulative, effects to measure. They also expected fish living in sub-ideal temperatures would experience more stress related to the high CO2 concentrations and that female fish would experience the greatest growth deficits.

The researchers also used the opportunity to study if there were sex-determination impacts on the population in the varying CO2 conditions. Sex-determination in Atlantic silversides depends on temperature, but the influence of seawater pH is unknown. In some freshwater fish, low pH conditions produce more males in the population. However, they did not find any evidence of the high CO2 levels impacting sex differentiation in the population. And the growth males and females appeared to be equally affected by high CO2.

“What we found is a pretty consistent response in that if you rear these fish under ideal conditions and feed them pretty controlled amounts of food, not over-feeding them, high CO2 conditions do reduce their growth in measurable amounts,” says Murray.

They found a growth deficit of between five and ten percent, which Murray says amounts to only a few millimeters overall, but the results are consistent. The fish living at less ideal temperatures and more CO2 experienced greater reductions in growth.

Murray concludes that by addressing potential shortcomings of previous studies, the data are clear: “Previous studies have probably underestimated the effects on fish growth. What our paper is demonstrating is that indeed if you expose these fish to high CO2 for a significant part of their life cycle, there is a measurable reduction in their growth. This is the most important finding of the paper.”

This work was funded by the National Science Foundation grant number OCE #1536165. You can follow the researchers on Twitter @baumannlab1 and @CMurray187.

https://today.uconn.edu/2020/08/uconn-research-carbon-ocean-can-lead-smaller-fish/

UConn Marine Sciences Professor Ann Bucklin presented a Webinar on July 22, 2020 hosted by the Marine Biodiversity Observation Network (MBON), as well as other international programs focused on marine biodiversity, including GOOS, OBPS, OBIS, and OceanObs RCN, as well as SCOR. The webinar focused on ongoing activities of the SCOR Working Group, MetaZooGene: Toward a new global view of marine zooplankton biodiversity based on DNA metabarcoding and reference DNA sequence databases. The presentation was followed by a Question & Answer session with three MetaZooGene-member Panelists: Katja Peijnenburg, Todd O’Brien, and Leocadio Blanco-Bercial. The Webinar was recorded and the video (and presentation PDF) can be viewed at this link: www.metazoogene.org/mbon-webinar-2020. Please feel free to share the link with interested colleagues and students.

Ann Bucklin (Professor of Marine Sciences) has been chosen to receive the Faculty Excellence in Research and Creativity-Sciences Award. This award is given by the UConn Foundation Alumni Relations Office in recognition of research excellence and highest level of creativity to enhance the University’s academic and creative reputation. The award acknowledges significant and/or creative contributions to a field of knowledge or area of inquiry.

https://today.uconn.edu/2020/06/tiny-shards-tons-sea-plastic-pollution-presents-challenge-labs-beaches-society/