The Role of Microbes in the World's Oceans
Sun, April 18, 2021

The Role of Microbes in the World's Oceans

 

 

All life on Earth evolved from microorganisms. They cycle minerals and nutrients through the soil, water, and the atmosphere and also help grow and digest the food we eat. Without these microorganisms, life as we know it wouldn't exist. Just because they are invisible to the naked eye, doesn't mean they are useless. While these organisms exist in land, rivers, and lakes, huge numbers of these are found in the world’s oceans.

Microorganisms such as bacteria, viruses, and protists fundamentally influence the ocean's ability to sustain life on Earth. Rick Cavicchioli, a professor and microbiologist at the School of Biotechnology and Biomolecular Sciences at UNSW Sydney, said that microorganisms support the existence of all higher lifeforms and are critically important in regulating climate change. However, they are the most underrated organisms because not all textbooks or websites talk about them. 

 

One Trillion Microbial Species

Many microbes  are keepers of healthy ecosystems. They clean the oceans of wastes and often defend habitats against disease. They can even live in some of the most extreme environments such as boiling hydrothermal vents and underground glacial lakes in the Antarctic. Scientists also said that they were even the first life on the planet, living without oxygen in an ancient ocean.

A 2016 study conducted by biologists at Indiana University provided a rigorous estimate of the number of microbial species on Earth. The study was funded by the National Science Foundation to better understand the scope of life on Earth by filling major gaps in humanity's knowledge about the planet's biodiversity. "This research offers a view of the extensive diversity of microbes on Earth. It also highlights how much of that diversity still remains to be discovered and described,” Simon Malcomber, director of the NSF's Dimensions of Biodiversity program, said. 

 

 

The researchers wanted to correct earlier attempts to estimate the number of species on Earth, where scientists simply ignored microorganisms or were informed by older datasets that were based on biased techniques or questionable extrapolations. According to Science Daily, an American website that aggregates press releases and publishes lightly edited press releases about science, the team combined microbial, plant and animal community datasets from government, academic and citizen science sources. This made it the largest-ever analysis of microbial data. 

The team was also able to gather data from microbial sampling efforts over the past several years, including the collection of human-related microorganisms by the National Institutes of Health's Human Microbiome Project; aquatic, terrestrial and host-related microorganisms by the Earth Microbiome Project, and marine microorganisms by the Tara Oceans Expedition. These resulted in 20,376 sampling efforts on bacteria, archaea, and microscopic fungi and 14,862 sampling efforts on communities of trees, birds, and mammals.

The findings revealed that Earth may be home to one trillion species, with only 1,000th of 1% now identified. "Until now, we haven't known whether aspects of biodiversity scale with something as simple as the abundance of organisms. As it turns out, the relationships are not only simple but powerful, resulting in the estimate of upwards of 1 trillion species,” co-author Kenneth J. Locey, a postdoctoral fellow in the IU Bloomington College of Arts and Sciences' Department of Biology, said. 

 

Regulating Climate Change

Scientists hope to raise awareness about how these tiny living organisms can influence climate change and how they will be impacted by a shifting climate. Last year, they made a plea for the world to stop ignoring the “unseen majority” of our planet’s biodiversity and ecosystem. A 2019 study by researchers from the University of Southern California revealed that marine microbes play an important role in how Earth regulates climate. 

Bacteria and unicellular algae play a particularly important role as they form the basis of the food chains. Photosynthetic bacteria and unicellular algae in the oceans, for instance, produce close to 50% of the oxygen in our atmosphere. They are at the base of the marine food chain, which is organized in complex ecosystems composed of viruses, bacteria, protists and a myriad of tiny multicellular organisms

 

 

The researchers trolled a 3,000-mile-long swath of the eastern Atlantic Ocean and the Mediterranean Sea in 2014 and sampled microorganisms in the water column down to 200 meters. They aimed to find how widespread rhodopsins are and in what conditions they are favored. Rhodopsins, a sunshine-grabbing pigment, have light-sensitive protein systems in their cell membranes that trap sunlight, an adaptation analogous to how rods and cones in the human eye gather light. It is said that bacteria contain these pigments. 

The findings revealed that rhodopsin photosystems were much more abundant than previously realized. “Rhodopsins appear to be more abundant in a nutrient-poor ocean, and in the future, the ocean will be more nutrient-poor as temperatures change. So, with fewer nutrients near the surface, algae will have limited photosynthesis, and the rhodopsin process will be more abundant. We may have a shift in the future, which means the ocean won't be able to absorb as much carbon as it does today. So more CO2 gas may remain in the atmosphere, and the planet may warm faster,” Laura Gómez-Consarnau, assistant professor (research) of biology at the USC Dornsife College of Letters, Arts, and Sciences, explained.

A recent study quantified the way specific marine bacteria process a key chemical called dimethylsulfoniopropionate (DMSP). Phytoplankton, tiny marine algae that produce approximately half of the oxygen we breathe every day, produce enormous amounts of DMSP. MIT graduate student Cherry Gao said that this chemical is a major nutrient source of bacteria. "It satisfies up to 95% of bacterial sulfur demand and up to 15% of bacterial carbon demand in the ocean. So given the ubiquity and the abundance of DMSP, we expect that these microbial processes would have a significant role in the global sulfur cycle,” Gao said. 

According to Phys.org, an internet news portal that provides the latest news on science, the study can help scientists researchers understand key details of how these microscopic marine organisms can affect global-scale biogeochemical and climatic processes. The findings revealed that marine microorganisms produce more than a billion tons of DMSP, accounting for 10% of the carbon that gets taken up by phytoplankton. 

DMSP plays an important role in the way sulfur and carbon get consumed by microorganisms in the ocean and released into the atmosphere. The chemical is also responsible for most of the biologically derived sulfur that enters the atmosphere from the oceans.