Prochlorococcus and Climate Change
By Zachary Aronson-Paxton
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What are Prochlorococcus?
Prochlorococcus is a gram negative, coccus bacteria species in the genus cyanobacteria. Prochlorococcus is an aquatic autotroph, found throughout the planet's oceans (Biller et al. 2015). Earth’s oxygen-rich atmosphere is the result of Cyanobacteria and their mass amounts of photosynthesis. Specifically, Prochlorococcus is one of the most abundant autotrophic bacteria in the planet’s oceans (Biller et al. 2015). Prochlorococcus can number up to 70,000 cells in a milliliter of ocean water (Campbell et al. 1998). These vast quantities produce a significant percentage of Earth’s entire photosynthetic output and up to 79 percent of the North Atlantic Ocean’s entire primary production (Biller et al. 2015) (Li 1994). As a result of their large photosynthetic potential, they are a key organism in the fight against climate change and the sequestration of atmospheric carbon. Prochlorococcus uptake more carbon dioxide to undergo photosynthesis than they use up in respiration, creating a stock of carbon inside each organism (Li 1994). When Prochlorococcus dies, it sinks to the bottom of the ocean and is buried, eventually forming oil in what is known as the ocean biological pump (Resplandy et al. 2019). In this way, Prochlorococcus serve as a sink for atmospheric carbon and have an impact on climate change.
The Effect of Climate Change on Prochlorococcus
How does climate change influence the number and efficacy of Prochlorococcus microbes throughout the planet's oceans?
Anthropogenic change is affecting the planet in many ways, most of them unanticipated by scientists. With the projection of continued global change, modeling the future changes set to affect various ecosystems is essential. Since Prochlorococcus is one of the most abundant sinks of atmospheric carbon dioxide, modeling the effects of planetary changes can potentially predict greater, unanticipated changes caused by Prochlorococcus. A decrease in Prochlorococcus and other autotrophic microbes could result in a larger than expected build up of greenhouse gasses as a result of these photosynthetic organisms’ carbon sequestration potential. Greenhouse gas build up, the main cause of global warming, is an essential factor in ecological dynamics across the planet. While Prochlorococcus has evolved for photosynthesis in environments with various different light availability and depths, the rate of anthropogenic change far outpaces Prochlorococcus’ evolution. Various human changes are projected to both increase and decrease the productivity of Prochlorococcus in the Atlantic Ocean.
Decrease in Prochlorococcus Functionality
Rapid global change is expected to decrease some aspects of Prochlorococcus function in the environment. The increase of atmospheric carbon dioxide can actually increase the vulnerability of Prochlorococcus (Hennon et al. 2018). While carbon dioxide is a reactant of photosynthesis and is commonly seen as a mechanism for increased phototrophic production, an increased carbon dioxide concentration can alter Prochlorococcus’ metabolism and microbial interactions with Alteromonas (Hennon et al. 2018). These shifts, a result of ocean acidification related to carbon dioxide levels, could eventually lead to oxidative stress. While oxygen is essential for cellular respiration, it is toxic to many cellular components due to its redox potential. Oxidative stress would lead to an overall decrease in Prochlorococcus productivity, meaning less carbon sequestration and a significant effect on global temperatures.
In addition to oxidative stress, Prochlorococcus functionality is also reduced by human produced plastic litter in the ocean (Tetu et al. 2019). Plastic bags made out of high-density polyethylene (HDPE) and other plastics made out of polyvinyl chloride (PVC) degrade to plastic leachates in the ocean (Tetu et al. 2019). The leachates, present in the marine ecosystem, directly affect the microbial communities around them. Concentration increases in plastic leachates cause decreased levels of photosynthesis in Prochlorococcus (Tetu et al. 2019). The higher the concentration of plastics, the less oxygen produced and the less carbon dioxide taken up. This decreased Prochlorococcus productivity has large implications on the amount of global photosynthesis and atmospheric carbon dioxide. Exposure to plastic leachates also decreases the growth rate of Prochlorococcus (Tetu et al. 2019). Plastic pollution not only impairs photosynthesis in Prochlorococcus, but it also decreases the growth rate, leading to a smaller population size of cells and a further decrease in primary production. Anthropogenic change such as plastic pollution and high atmospheric carbon dioxide result in lower primary production levels of the most abundant aquatic phototroph.
Prochlororcoccus’ Impact on the Oceans
How does Prochlorococcus’ large scale photosynthetic processes affect ocean ecosystems?
Include some current research, with at least one figure showing data.
Prochlororcoccus’ Effect on the Changing Planet
Does Prochlorococcus have a direct impact on the planet’s atmosphere and the process of climate change?
Include some current research, with at least one figure showing data.
Conclusion
References
Authored for BIOL 238 Microbiology, taught by Joan Slonczewski, 2023, Kenyon College
