Bacteria
SAR86
Craig Carlson
SAR86
Bacteria in the SAR86 group, named for the Sargasso Sea, are among the most abundant microbes in the surface ocean. Like many microbial groups in the ocean, no one has yet succeeded in culturing SAR86 in the laboratory. They are photoheterotrophic, meaning they are able to harvest energy from light but also get energy from eating carbon-kind of like a carnivorous plant.
Beggiatoa
Katherine Dawson
Beggiatoa
Beggiatoa are a genus of chemosynthetic microbes, meaning they can grow using inorganic sulfur and inorganic carbon. Beggiatoa form white mats of filamentous cells on the ocean floor in areas that are rich in hydrogen sulfide, such as hydrothermal vents or polluted water. Sulfide-oxidizing relatives of Beggiatoa are the chemosynthetic powerhouses that support massive colonies of tubeworms at hydrothermal vent systems.
Pelagibacter ubique
Courtesy of Xiaowei Zhao
Pelagibacter ubique
Pelagibacter is a representative of a group of marine bacteria known as the SAR11 clade. 'SAR' stands for Sargasso Sea, where they were first discovered in 1990 using DNA sequencing. It took another twelve years before scientists were able to grow them in the laboratory. Microbes in the SAR11 clade are the most abundant heterotrophic, or carbon-eating, bacteria in the ocean and can make up 25 percent or more of microbial cells at any given time. They are among the smallest cells in the ocean.
Desulfobacterium autotrophicum
© John Wiley and Sons
Desulfobacterium autotrophicum
Sulfate-reducing bacteria like D. autotrophicum are important for breaking down organic matter (think feces or decomposing algae and animals) in marine sediments at the bottom of the ocean and turning it back into carbon dioxide. In some shallow environments, these bacteria serve as the primary pathway for the breakdown of organic matter.
Roseobacter
Jeremy Ethan Schreier
Roseobacter
Marine roseobacters are an abundant and versitile group of bacteria. Members of the Roseobacteraceae family have been found in most marine environments-from sediments and polar sea ice, to tropical coral reefs and the open ocean. In coastal marine waters, they can make up to 25 percent of the bacterial biomass and play a large role in global carbon and sulfur cycling. The roseobacter Ruegeria pomeroyii was one of the first marine bacteria to have its genome sequenced.
Marinimicrobia
Pixabay
Marinimicrobia
The Marinimicrobia are an entire phylum of marine bacteria that have yet to be cultured in a lab. Originally discovered in the Sargasso Sea, they were known only by the code 'SAR406' for many years. New techniques in DNA sequencing have allowed scientists to sequence the genomes of these single cells from the ocean without having to first culture them. Using this technique, scientists have discovered that Marinimicrobia may play important roles in many elemental cycles in the ocean including the sulfur and nitrogen cycles.
Procholorococcus marina
Department of Energy
Procholorococcus marina
Prochlorococcus are cyanobacteria estimated to be more abundant than any other photosynthetic organisms on the planet. Together with their close relative Synechococcus, they can account for up to 40 percent of the carbon drawn from the atmosphere and introduced into the ocean food webs, and up to half of the oxygen produced on the planet every year.
SAR202
Seabird McKeon
SAR202
Yet another group of bacteria known only by its DNA sequences, SAR202 belong to the Chloroflexi phylum. They are primarily inhabitants of the dark ocean, where they are thought to specialize in eating large organic compounds that other microbes have difficulty breaking down. The name Monstramaria has been proposed for one group of SAR202, meaning "sea monster."
Polaribacter
Jarone Pinhassi
Polaribacter
Besides the cyanobacteria and proteobacteria, Bacteroidetes is the the third major phylum of bacteria found in the ocean. They are thought to be specialists at breaking down complex marine particles and they have special adaptations that allow them to grow on surfaces, including genes that specialize in surface attachment and gliding movement. Colorful Polaribacter is able to harvest energy from both organic carbon and light.
Archaea
Nitrosopelagicus brevis
William Orsi
Nitrosopelagicus brevis
While many archaea are thought of as extremeophiles thriving at high temperatures and pressure, many thaumarchaea, which includes Nitrosopelagicus, grow in "normal" conditions. They carry out the first step of nitrification, a central process in the nitrogen cycle. Because they get their energy from an inorganic source and fix carbon, they have a unique metabolism called chemolithoautotrophy.
Methanocaldocococcus jannaschii
UC Berkeley Electron Microscope Lab
Methanocaldocococcus jannaschii
M. jannaschii was isolated from a hydrothermal vent and is capable of tolerating extreme conditions of temperature and pressure, up to 98°C/208°F. Methanogenic archaea, of which M. jannaschii is just one example, are responsible for 75 percent of emissions of the greenhouse gas methane into the atmosphere. M. jannaschii was the first archaea to have its genome seqeuenced.
Lokiarchaea
Centre for Geobiology (University of Bergen, Norway) by R.B. Pedersen
Lokiarchaea
Discovered only a few years ago at a hydrothermal vent off the coast of Iceland, these archaea share several important genetic signatures with eukaryotes meaning they could be our closest relatives in the prokaryotic (cells with no nucleus) world.
Eukaryotes
Eupelagonema oceanica
Noriko Okamoto
Eupelagonema oceanica
E. oceanica is a representative of a mysterious, but widespread and diverse, group of protists called the marine diplonemids. Diplonemids lack chloroplasts, so they survive by eating bacteria or other small protists. No cultures of E. oceanica exist and only recently it was photographed for the first time and had its genome sequenced from a single cell.
Emiliana huxleyii
Emiliana huxleyii
'E. hux,' as it is affectionately called, is a coccolithophorid covered in unique calcium carbonate plates. These small phytoplankton are one of the largest consumers of calcium carbonate in the ocean, making them important sinks of carbon dioxide from the atmosphere. Blooms of E. hux can be seen from space. When coccolithophores die en masse they eventually form into beds of limestone and chalk, which we can see remnants of today in the famous White Cliffs of Dover in England.
Acantharia
Ernst Haekel
Acantharia
These beautiful plankton are found only in the ocean. They are distinguished by their delicate spicules that radiate from the center of the cell to form dramatic snowflake-like structures. Their skeletons are made of strontium sulfate, an unusual mineral in the microbial world.
Thalassiosira pseudonana
Thalassiosira pseudonana
T. pseudonana is a diatom, a group of photosynthetic algae that make delicate glass houses of silica. They are widespread in the ocean, particularly in coastal areas. Because they fix carbon from the atmosphere, they are at the base of the ocean's food web. Sometimes diatoms are mistakenly referred to as tiny plants, but diatoms evolved along a completely separate branch on the tree of life.
Solenicola setigera
Fernando Gomez
Solenicola setigera
Solenicola is a representative of an abundant, almost completely uncultured group of protists known as MAST, which stands for marine stramenopiles. These organisms play an important ecological role in the ocean as grazers or predators on marine bacteria. Some MAST are also parasites, attaching to the outside of phytoplankton. Solenicola belong to the MAST-3 group; the most abundant and widespread group in the ocean are known as MAST-4.
Cafeteria roenbergensis
Tamara Clark, CC-BY-NC-SA
Cafeteria roenbergensis
A major role for microbial eukaryotes in marine ecosystems is eating bacteria and keeping their abundance in check. C. roenbergensis is one such flagellate with a voracious appetite. It can swim rapidly to ingest its prey. Cafeteria species are widely distributed in coastal environments.
Ceratium spp.
Ceratium spp.
These beautiful phytoplankton are members of the dinoflagellates, a diverse group of algae that moves around with two flagella (small appendages that aid in movement). Ceratium are characterized by two charismatic "horns." They are photosynthetic organisms that can form large blooms in coastal waters, often referred to as red tides. Unlike other eukaryotic algae that surround their cells with a mineral skelton, these dinoflagellates make their armored plates out of cellulose.
Ostreococcus tauri
Martin Hohmann-Marriott
Ostreococcus tauri
This little guy is one of the smallest eukaryotic algae in the ocean, smaller than some species of bacteria, making them "pico" eukaryotes. They are frequently found in coastal waters and have one of the simplest cellular structures of marine algae, containing a single chloroplast.
Salpingoeca rosetta
Ben Larson
Salpingoeca rosetta
Choanoflagellates are distinguished by their collars, which surround a long flagellum used both to swim and to generate water currents that trap bacterial prey inside the collar. Choanoflagellates are the closest living single-celled relatives of multicellular animals. Some choanoflagellates, like S. rosetta, can form rose-like multicellular colonies during cell division. In the ocean, there are many diverse groups of uncultured choanoflagellates that are important grazers of bacteria.