Micromonas | |
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Micromonas pusilla | |
Scientific classification | |
(unranked): | Viridiplantae |
Division: | Chlorophyta |
Class: | Mamiellophyceae |
Order: | Mamiellales |
Family: | Mamiellaceae |
Genus: | Micromonas Manton & Parke 1960 |
Species | |
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Micromonas is a genus of green algae in the family Mamiellaceae . [1] [2]
Micromonas is a widespread prasinophyte alga that is very small in size, motile, and phototactic. [3] Before characterization and naming of a second species, Micromonas commoda [4] through genome analysis, [5] Micromonas pusilla was considered to be the only species in the genus. [6] [7] This led to a disproportionate amount of research discussing a single species and the suggestion that it was the dominant photosynthetic picoeukaryote in some marine ecosystems. [8] Unlike many marine algae, this single species was thought to be distributed widely in both warm and cold waters, but genome sequencing confirmed indications from single-gene studies [9] [10] that its global distribution really reflected presence of multiple species occupying different niches in the ocean. [5] [3]
Some studies have divided Micromonas pusilla into 3 to 5 different clades despite their similarity in morphologies and habitats. [11] [12] Varying ratios of clades contribute to the M. pusilla population throughout the marine ecosystem leading to the hypothesis of clades arising based on niche occupation and susceptibility to virus infection. [12] Other studies have established the presence of at least seven phylogenetically distinct species for which global sequence analyses are beginning to delineate clear differences in the ocean regions they inhabit, with only some of the species actually co-occurring in the same environment. [13] [14] [15]
Micromonas pusilla is considered the first picoplankton studied, when it was discovered and named Chromulina pusilla in the 1950s by R. Butcher. [16] Later, electron micrographs by the English scientists, Irene Manton and Mary Park, in the 1960s provided further details on M. pusilla. [16]
Micromonas is a group of small unicellular pear-shaped micro-algae that do not have a visible cell wall.<refname="genomes" /> [17] [4] Just like other members in the class, they have a single mitochondrion and a single chloroplast, which covers almost half of the cell. [4] [18] They are able to swim due to the presence of a scale-less flagellum. [4] [18] [6] The axonemal structure of the flagellum for this genus is different in that the peripheral microtubules do not extend up to the termination of the central pair of microtubules, allowing a visible investigation of the motion of the central pair. [17] [19] [16] In Micromonas, the central pair constantly rotates in an anti-clockwise direction, despite the motion of other components of the flagellum. [17] [19]
While the cell size, shape and the location of insertion of the flagellum into the cell are similar among strains and genetic clades, the variation in respective hair point length results in different lengths of the flagella within the genus. [6]
The antibiotic susceptibility was determined using a single strain of M. pusilla with the purpose to produce axenic cultures to be used in studies and experiments. [20] The strain of M.pusilla was tested with a range of antibiotics to determine the possible effects of the particular antibiotic. [20]
Resistance: [20] benzylpenicillin, gentamicin, kanamycin, neomycin, streptomycin
Sensitive: [20] chloramphenicol, polymyxin B
For M. pusilla, sensitivity towards an antibiotic is likely defined by the impairment of growth, rather than a lethal effect, when subjected to bactericidal levels of that particular antibiotic. [20] The susceptibility of other strains of M. pusilla towards this set of antibiotics should be the same. [20]
Micromonas diverged early on from the lineage that led to all modern terrestrial plants. Individual species have very similar 18S ribosomal RNA gene sequences, a comparison often used to determine microscopic speciation, however, <90% of different genes are shared between the two genome sequenced Micromonas species. [5] They have more notable differences in the V1-V2 region of the 16S ribosomal RNA genes (located in the chloroplast genome). [14] More recent analyses show just how divergent they are in relation to other green lineage members, specifically land plants and chlorophyte green algae. [15]
Although Micromonas pusilla was thought to represent a single species, genetic studies have shown that Micromonas lineages diverged from each other as early as 65 million years ago, accumulating a large amount of genetic differences. The lack of morphological differentiation means that Micromonas pusilla may be considered a cryptic species complex. [9]
The original Micromonas reference genome(s) were created from strain CCMP1545 isolated from the North Atlantic and deposited in a culture collection in the 1980s, and strain CCMP2709 (RCC299 prior to being rendered axenic and clonal), isolated in 1998 from an Equatorial Pacific sample. [5] These strains had been cultured for decades and are available from the National Center for Marine Algae and Microbiota (NCMA, US) and the Roscoff Culture Collection (RCC, FR).
Micromonas reproduces asexually through fission. [17] It has been observed that M. pusilla shows variability in optical characteristics, for example cell size and light scattering, throughout the day. [21] There is an increase in these measurements during the period with light, followed by a decrease during period without light. [21] [22] This coincides with the findings that proteomic profiles change over the diel cycle, with an increase in expression of proteins related to cell proliferation, lipid and cell membrane restructuring in the dark when cells start dividing and become smaller. [22] However, the expression levels of genes and proteins can still vary within the same metabolic pathway. [22] It has also been suggested that the structure of 3’ UTR may play a role in the regulatory system. [22]
Micromonas species still share the same collection of photosynthetic pigments as the members of the class Mamiellophyceae, [6] which includes the common pigments chlorophyll a and chlorophyll b, [23] as well as prasinoxanthin (xanthophyll K), the first algal carotenoid being assigned with a structure that has a γ-end group. [24] It has been discovered that most of its xanthophylls are in the oxidized state and show similarities to ones possessed by other important marine planktons like diatoms, golden and brown algae, and dinoflagellates. [25] In addition, there is another pigment called Chl cCS-170 can be found in some strains of Micromonas and Ostreococcus living in deeper part of the ocean, which may indicate a potential adaptation for organisms that reside under low light intensity, [6] however, at least for Ostreococcus these strains are found throughout the water column in open ocean gyres, including in surface waters. [26]
The light-harvesting complexes of Micromonas are distinguishable from other green algae in terms of pigment composition and stability under unfavorable conditions. [23] It has been shown that these proteins use three different pigments for light harvesting, and they are resistant to high temperature and the presence of detergent.
Even though the chloroplasts, which are suggested to be originated from Cyanobacteria via endosymbiosis, [27] from Micromonas do not have a surrounding peptidoglycan layer, the peptidoglycan biosynthesis pathway is found to be complete in M.pusilla and partial in M. commoda, with the presence of some relevant enzymes only. [4] While the role of this pathway for Micromonas is still under investigation, this observation shows a lineage for different species of Micromonas along with glaucophyte algae which still have their chloroplasts covered with peptidoglycan. [4]
Micromonas make up a significant amount of picoplanktonic biomass and productivity in both oceanic and coastal regions. [8] The abundance of Micromonas has increased over the past decade. Evidence shows these spikes in numbers are induced through climate change, which has been felt more drastically in the Arctic. [4] Many green algal species have been considered solely photosynthetic, and this appears to be the case for Micromonas. Some years ago a study indicated that Micromonas had a predatory mixotrophic lifestyle that might have large impacts on prokaryotic populations within the Arctic. [28] Due to the large consumption of prokaryotes by Micromonas, this study and others building on it, suggested it might underlie why photosynthetic picoeukaryotes appear to be increasing in the arctic. [28] However, the authors of that study lost the strain used, and two subsequent studies by other laboratories were unable to replicate the results, concluding that Micromonas, including M. polaris, is not a predatory mixotroph. [29] [30]
Viruses are important in the balance of marine ecosystem by regulating the composition of microbial communities, but their behaviors can be affected by several factors including temperature, mode of infection and host conditions. [31] [32] There is an increasing number of Micromonas-infecting virus being discovered and studied, including studies of transcriptional responses to infection under differing nutrient conditions. [33]
There are currently 45 viral strains identified that coexist with M. pusilla populations. [12] Virus infectivity is dependent on the host strain, light availability and virus adsorption. [34]
Per day average of death due to virus lysis is estimated to be about 2 to 10% of the M. pusilla population. [34]
It is the first phycodnavirus being isolated from polar ocean waters. [37] It can infect M. polaris, which is the polar ecotype of Micromonas that has adapted to waters with low temperatures. [37]
Evidence suggests that the increase in temperature due to climate change may shift the clonal composition of both the virus and host. [37]
With the growing population in the world, there is an increased demand for wild fishes and algae for their source of polyunsaturated fatty acids (PUFA), which is required for growth and development, as well as the maintenance of health in humans. Recent research is investigating an alternative mechanism for production of PUFA by using acyl-CoA Δ6-desaturase, an enzyme present in M. pusilla, with plants. The M. pusilla strain of acyl-CoA Δ6-desaturase is highly effective in the polyunsaturated fatty acid synthesis pathway due to its strong binding preference for omega-3 substrates in land plants. [38]
The dinoflagellates are a monophyletic group of single-celled eukaryotes constituting the phylum Dinoflagellata and are usually considered protists. Dinoflagellates are mostly marine plankton, but they also are common in freshwater habitats. Their populations vary with sea surface temperature, salinity, and depth. Many dinoflagellates are photosynthetic, but a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey.
Prochlorococcus is a genus of very small (0.6 μm) marine cyanobacteria with an unusual pigmentation. These bacteria belong to the photosynthetic picoplankton and are probably the most abundant photosynthetic organism on Earth. Prochlorococcus microbes are among the major primary producers in the ocean, responsible for a large percentage of the photosynthetic production of oxygen. Prochlorococcus strains, called ecotypes, have physiological differences enabling them to exploit different ecological niches. Analysis of the genome sequences of Prochlorococcus strains show that 1,273 genes are common to all strains, and the average genome size is about 2,000 genes. In contrast, eukaryotic algae have over 10,000 genes.
Cafeteria roenbergensis is a small bacterivorous marine flagellate. It was discovered by Danish marine ecologist Tom Fenchel and named by him and taxonomist David J. Patterson in 1988. It is in one of three genera of bicosoecids, and the first discovered of two known Cafeteria species. Bicosoecids belong to a broad group, the stramenopiles, also known as heterokonts (Heterokonta) that includes photosynthetic groups such as diatoms, brown, and golden algae, and non-photosynthetic groups such as opalinids, actinophryid "heliozoans", and oomycetes. The species is found primarily in coastal waters where there are high concentrations of bacteria on which it grazes. Its voracious appetite plays a significant role in regulating bacteria populations.
Photosynthetic picoplankton or picophytoplankton is the fraction of the photosynthetic phytoplankton of cell sizes between 0.2 and 2 μm. It is especially important in the central oligotrophic regions of the world oceans that have very low concentration of nutrients.
Cyanophages are viruses that infect cyanobacteria, also known as Cyanophyta or blue-green algae. Cyanobacteria are a phylum of bacteria that obtain their energy through the process of photosynthesis. Although cyanobacteria metabolize photoautotrophically like eukaryotic plants, they have prokaryotic cell structure. Cyanophages can be found in both freshwater and marine environments. Marine and freshwater cyanophages have icosahedral heads, which contain double-stranded DNA, attached to a tail by connector proteins. The size of the head and tail vary among species of cyanophages. Cyanophages infect a wide range of cyanobacteria and are key regulators of the cyanobacterial populations in aquatic environments, and may aid in the prevention of cyanobacterial blooms in freshwater and marine ecosystems. These blooms can pose a danger to humans and other animals, particularly in eutrophic freshwater lakes. Infection by these viruses is highly prevalent in cells belonging to Synechococcus spp. in marine environments, where up to 5% of cells belonging to marine cyanobacterial cells have been reported to contain mature phage particles.
Phycodnaviridae is a family of large (100–560 kb) double-stranded DNA viruses that infect marine or freshwater eukaryotic algae. Viruses within this family have a similar morphology, with an icosahedral capsid. As of 2014, there were 33 species in this family, divided among 6 genera. This family belongs to a super-group of large viruses known as nucleocytoplasmic large DNA viruses. Evidence was published in 2014 suggesting that specific strains of Phycodnaviridae might infect humans rather than just algal species, as was previously believed. Most genera under this family enter the host cell by cell receptor endocytosis and replicate in the nucleus. Phycodnaviridae play important ecological roles by regulating the growth and productivity of their algal hosts. Algal species such Heterosigma akashiwo and the genus Chrysochromulina can form dense blooms which can be damaging to fisheries, resulting in losses in the aquaculture industry. Heterosigma akashiwo virus (HaV) has been suggested for use as a microbial agent to prevent the recurrence of toxic red tides produced by this algal species. Phycodnaviridae cause death and lysis of freshwater and marine algal species, liberating organic carbon, nitrogen and phosphorus into the water, providing nutrients for the microbial loop.
Ostreococcus is a genus of unicellular coccoid or spherically shaped green algae belonging to the class Mamiellophyceae. It includes prominent members of the global picoplankton community, which plays a central role in the oceanic carbon cycle.
The prasinophytes are a group of unicellular green algae. Prasinophytes mainly include marine planktonic species, as well as some freshwater representatives. The prasinophytes are morphologically diverse, including flagellates with one to eight flagella and non-motile (coccoid) unicells. The cells of many species are covered with organic body scales; others are naked. Well studied genera include Ostreococcus, considered to be the smallest free-living eukaryote, and Micromonas, both of which are found in marine waters worldwide. Prasinophytes have simple cellular structures, containing a single chloroplast and a single mitochondrion. The genomes are relatively small compared to other eukaryotes . At least one species, the Antarctic form Pyramimonas gelidicola, is capable of phagocytosis and is therefore a mixotrophic algae.
Picoeukaryotes are picoplanktonic eukaryotic organisms 3.0 μm or less in size. They are distributed throughout the world's marine and freshwater ecosystems and constitute a significant contribution to autotrophic communities. Though the SI prefix pico- might imply an organism smaller than atomic size, the term was likely used to avoid confusion with existing size classifications of plankton.
Ostreococcus tauri is a unicellular species of marine green alga about 0.8 micrometres (μm) in diameter, the smallest free-living (non-symbiotic) eukaryote yet described. It has a very simple ultrastructure, and a compact genome.
Marine microorganisms are defined by their habitat as microorganisms living in a marine environment, that is, in the saltwater of a sea or ocean or the brackish water of a coastal estuary. A microorganism is any microscopic living organism or virus, which is invisibly small to the unaided human eye without magnification. Microorganisms are very diverse. They can be single-celled or multicellular and include bacteria, archaea, viruses, and most protozoa, as well as some fungi, algae, and animals, such as rotifers and copepods. Many macroscopic animals and plants have microscopic juvenile stages. Some microbiologists also classify viruses as microorganisms, but others consider these as non-living.
In biology, a pathogen, in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ.
Alteromonas macleodii is a species of widespread marine bacterium found in surface waters across temperate and tropical regions. First discovered in a survey of aerobic bacteria in 1972, A. macleodii has since been placed within the phylum Pseudomonadota and is recognised as a prominent component of surface waters between 0 and 50 metres. Alteromonas macleodii has a single circular DNA chromosome of 4.6 million base pairs. Variable regions in the genome of A. macleodii confer functional diversity to closely related strains and facilitate different lifestyles and strategies. Certain A. macleodii strains are currently being explored for their industrial uses, including in cosmetics, bioethanol production and rare earth mining.
Alexandra (Alex) Z. Worden is a microbial ecologist and genome scientist known for her expertise in the ecology and evolution of ocean microbes and their influence on global biogeochemical cycles.
Picozoa, Picobiliphyta, Picobiliphytes, or Biliphytes are protists of a phylum of marine unicellular heterotrophic eukaryotes with a size of less than about 3 micrometers. They were formerly treated as eukaryotic algae and the smallest member of photosynthetic picoplankton before it was discovered they do not perform photosynthesis. The first species identified therein is Picomonas judraskeda. They probably belong in the Archaeplastida as sister of the Rhodophyta.
Prasinovirus is a genus of large double-stranded DNA viruses, in the family Phycodnaviridae that infect phytoplankton in the Prasinophyceae. There are three groups in this genus, including Micromonas pusilla virus SP1, which infects the cosmopolitan photosynthetic flagellate Micromonas pusilla.
Mimoreovirus is a genus of viruses, in the family Reoviridae, in the subfamily Sedoreovirinae. The only isolate infects the marine photosynthetic protist Micromonas pusilla, a prasinophyte. There is only one species in this genus: Micromonas pusilla reovirus.
Corina P. D. Brussaard is a leading scientist for Antarctic viral ecology working for the Royal Institute of Sea Research (NIOZ) and is a Special Professor of Viral Ecology at the Institute for Biodiversity and Ecosystem Dynamics of the University of Amsterdam (UvA).
Algal viruses are the viruses infecting algae, which are photosynthetic single-celled eukaryotes. As of 2020, there were 61 viruses known to infect algae. Algae are integral components of aquatic food webs and drive nutrient cycling, so the viruses infecting algal populations also impacts the organisms and nutrient cycling systems that depend on them. Thus, these viruses can have significant, worldwide economic and ecological effects. Their genomes varied between 4.4 to 560 kilobase pairs (kbp) long and used double-stranded Deoxyribonucleic Acid (dsDNA), double-stranded Ribonucleic Acid (dsRNA), single-stranded Deoxyribonucleic Acid (ssDNA), and single-stranded Ribonucleic Acid (ssRNA). The viruses ranged between 20 and 210 nm in diameter. Since the discovery of the first algae-infecting virus in 1979, several different techniques have been used to find new viruses infecting algae and it seems that there are many algae-infecting viruses left to be discovered
Phaeocystis globosa virus virophage, or PgVV, or Preplasmiviricota sp. Gezel-14T, is a polinton-like virus, which are small DNA viruses that are found integrated in protist genomes. Similar to virophages, PgVV requires a helper virus to replicate. Phaeocystis globosa virus virophage has a parasitic relationship with its helper virus species Phaeocystis globosa virus (PgV). They are a species of giant virus that infect algae of the genus Phaeocystis.