''Palpitomonas'' is a genus of biflagellated

protist A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists do not form a natural group, or clade, but are a paraphyletic grouping of all descendants of the last eukaryotic common ancest ...

s within the phylum

Cryptista Cryptista is a clade of alga-like eukaryotes. It is most likely related to Archaeplastida which includes plants and many algae, within the larger group Diaphoretickes. Other characteristic features of cryptophyte mtDNAs include large syntenic ...

'','' a clade of basal

eukaryote The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...

s. This genus is especially significant for understanding the early evolution of mitochondria,

flagella A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

, and the broader cryptist lineage. ''Palpitomonas'' is a key model organism for studying the phylogenetic origins of

mitochondria A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is us ...

and eukaryotic motility structures, such as

. One of the most common species in the genus of ''Palpitomonas'' is '' Palpitomonas bilix'', which has been used in genomic and phylogenetic studies due to its special

mitochondrial genome Mitochondrial DNA (mtDNA and mDNA) is the DNA located in the mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the DNA contained in ...

structure and basal phylogenetic position.

Introduction

''Palpitomonas'' is an important

organism An organism is any life, living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have be ...

for research on the origins of eukaryotic life. ''Palpitomonas'' ''bilix'' have some unique characteristics that are rare in the other

s, characterized by its small size, biflagellate structure, and unique mitochondrial. The genus ''Palpitomonas'' belongs to

, which includes other simple eukaryotic organisms like cryptophytes and

katablepharid The kathablepharids or katablepharids () are a group of heterotrophic flagellates closely related to cryptomonads. First described by Heinrich Leonhards Skuja in 1939, kathablepharids were named after the genus '' Kathablepharis''. This genus is ...

s. As a

bacterivore A bacterivore is an organism which obtains energy and nutrients primarily or entirely from the consumption of bacteria. The term is most commonly used to describe free-living, heterotrophic, microscopic organisms such as nematodes as well as many s ...

''Palpitomonas'' plays an ecological role in regulating microbial populations and

nutrient cycling A nutrient cycle (or ecological recycling) is the movement and exchange of inorganic and organic matter back into the production of matter. Energy flow is a unidirectional and noncyclic pathway, whereas the movement of mineral nutrients is cyc ...

marine ecosystem Marine ecosystems are the largest of Earth's aquatic ecosystems and exist in Saline water, waters that have a high salt content. These systems contrast with freshwater ecosystems, which have a lower salt content. Marine waters cover more than 7 ...

s by feeding on

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

and become a prey for larger microorganism

Taxonomy and classification

The genus ''Palpitomonas'' is part of the Cryptista phylum, which itself is situated within the

Diaphoretickes Diaphoretickes is a major group of eukaryote, eukaryotic organisms spanning over 400,000 species. The majority of the earth's biomass that carries out photosynthesis belongs to Diaphoretickes. In older classification systems, members of the Diaph ...

supergroup.

is a basal group of

s whose members are primarily aquatic and flagellated. The phylum

, as part of

, shares a common ancestor with other early-diverging eukaryotic groups, including the

Archaeplastida The Archaeplastida (or kingdom Plantae '' sensu lato'' "in a broad sense"; pronounced ) are a major group of eukaryotes, comprising the photoautotrophic red algae (Rhodophyta), green algae, land plants, and the minor group glaucophytes. It als ...

and the

SAR supergroup SAR is a highly diverse clade of eukaryotes, often considered a supergroup, that includes stramenopiles (heterokonts), alveolates, and rhizarians. It is a node-based taxon (under the Sar name), including all descendants of the three groups' ...

(

Stramenopile The stramenopiles, also called heterokonts, are protists distinguished by the presence of stiff tripartite external hairs. In most species, the hairs are attached to flagella, in some they are attached to other areas of the cellular surface, an ...

Alveolate The alveolates (meaning "pitted like a honeycomb") are a group of protists, considered a major unranked clade or superphylum within Eukaryota. They are currently grouped with the Stramenopiles and Rhizaria among the protists with tubulocristate ...

Rhizaria The Rhizaria are a diverse and species-rich clade of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus '' Paulinella'' in the phylum Cercozoa, they are all non-photosynthetic, but many Foraminifera ...

). Classification of ''Palpitomonas'' has evolved over time as molecular phylogenetic has revealed its position as one of the earliest-diverging eukaryotic lineages, particularly among the flagellated protists.

Scientific classification

* Domain:

Eukarya The eukaryotes ( ) constitute the domain of Eukaryota or Eukarya, organisms whose cells have a membrane-bound nucleus. All animals, plants, fungi, seaweeds, and many unicellular organisms are eukaryotes. They constitute a major group of l ...

* Supergroup:

* Phylum:

* Genus: Palpitomonas The genus ''Palpitomonas'' is closely related to other genus of

, including the Kathablepharids and Cryptophytes, but its specific evolutionary path remains an area of ongoing study.

Molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

analyses, particularly those involving ribosomal RNA (rRNA) sequences and

protein-coding genes The human genome is a complete set of nucleic acid sequences for humans, encoded as the DNA within each of the 23 distinct chromosomes in the cell nucleus. A small DNA molecule is found within individual mitochondria. These are usually treated s ...

, have demonstrated that ''Palpitomonas'' is a basal lineage within

, with close related to the early-diverging mitochondrial ancestors of other eukaryotes.

Phylogenetic position

Phylogenetic analyses In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as Computational phylogenetics, phylogenetic inference. It infers the relationship among organ ...

based on multigene datasets have shown ''Palpitomonas'' ''bilix'' as basal within the Cryptista clade, diverging before cryptophytes and

s. Its unique position in the

eukaryotic The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...

tree makes it instrumental for studying the divergence of eukaryotic lineages. ''Palpitomonas'' is also part of broader studies that question the

monophyly In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent comm ...

Hacrobia The cryptomonads-haptophytes assemblage is a proposed but disputed monophyletic grouping of unicellular eukaryotes that are not included in the SAR supergroup. Several alternative names have been used for the group, including Hacrobia (derived ...

, suggesting complex evolutionary relationships among early-diverging

s. Phylogenetic studies with 157-gene alignments have reinforced its position as a basal cryptist, adding clarity to its relationship with other

s such as cryptophytes. Palpitomonas 4

Morphology

''Palpitomonas'' ''bilix'', the primary species in this genus, has a distinctive

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines *Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies, ...

Cells Cell most often refers to: * Cell (biology), the functional basic unit of life * Cellphone, a phone connected to a cellular network * Clandestine cell, a penetration-resistant form of a secret or outlawed organization * Electrochemical cell, a d ...

are small approximately 3-8micrometer with unique structure with two l ateral flagella that different in function and position. The anterior flagellum is highly active but the posterior flagellum trails passively, helping the organism's characteristic "wobbling" motion. This biflagellate structure is significant for movement and feeding. Each cell is vacuolated with no

cell wall A cell wall is a structural layer that surrounds some Cell type, cell types, found immediately outside the cell membrane. It can be tough, flexible, and sometimes rigid. Primarily, it provides the cell with structural support, shape, protection, ...

allowing for flexibility. The mitochondria of ''Palpitomonas'' contain flat cristae, similar to those found in other cryptists, although distinct from the tubular

crista A crista (; : cristae) is a fold in the inner mitochondrial membrane, inner membrane of a mitochondrion. The name is from the Latin for ''crest'' or ''plume'', and it gives the inner membrane its characteristic wrinkled shape, providing a large a ...

e of

Katablepharid The kathablepharids or katablepharids () are a group of heterotrophic flagellates closely related to cryptomonads. First described by Heinrich Leonhards Skuja in 1939, kathablepharids were named after the genus '' Kathablepharis''. This genus is ...

a. Ultrastructural analysis shows a single

mitochondrion A mitochondrion () is an organelle found in the cell (biology), cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosine tri ...

with lobed extensions and an

endoplasmic reticulum The endoplasmic reticulum (ER) is a part of a transportation system of the eukaryote, eukaryotic cell, and has many other important functions such as protein folding. The word endoplasmic means "within the cytoplasm", and reticulum is Latin for ...

surrounding the

nucleus Nucleus (: nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucleu ...

. A

Golgi apparatus The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic Cell (biology), cells. Part of the endomembrane system in the cytoplasm, it protein targeting, packages proteins ...

is located between the

and

, and two microtubular roots support the basal bodies. The anterior flagellum of ''Palpitomonas'' possesses

mastigoneme Mastigonemes are lateral "hairs" that attach to protistan flagella. Flimsy hairs attach to the flagella of euglenid flagellates, while stiff hairs occur in stramenopile and cryptophyte protists.Hoek, C. van den, Mann, D. G. and Jahns, H. M. ( ...

s—bipartite hair-like structures that aid in movement and feeding by creating a current that draws in food particles.

Electron microscopy An electron microscope is a microscope that uses a beam of electrons as a source of illumination. It uses electron optics that are analogous to the glass lenses of an optical light microscope to control the electron beam, for instance focusing i ...

has shown that ''Palpitomonas'' doesn't has

ejectosome An ejectosome is a cellular organelle responsible for ejecting their contents from the cell. Two unrelated types of ejectosomes are described in the literature: # Cryptomonads have two types of characteristic extrusomes known as ejectosomes. # In ...

s an organelle used for rapid ejection of cell contents, which is present in cryptophytes but absent in

s and ''Palpitomonas''. This lack of

s and other features further distinguishes ''Palpitomonas'' from other cryptists. Palpitomonas 22

Mitochondrial genome and cytochrome c maturation

''Palpitomonas'' ''bilix'' has a distinctive

, organized as a linear DNA molecule with large inverted repeats at both ends. This linear mitochondrial genome structure, unusual among

s, is thought to have evolved independently in several lineages. It contains genes related to cytochrome c maturation (System I), a system inherited from bacterial ancestors. While related cryptists such as cryptophytes and kathablepharids utilize a different cytochrome c maturation system (System III), ''Palpitomonas'' retains the ancestral System I, making it an important model for studying mitochondrial evolution in eukaryotes.

Ecological role

''Palpitomonas'' play an ecological role in

marine environment A marine habitat is a habitat that supports marine life. Marine life depends in some way on the saltwater that is in the sea (the term ''marine'' comes from the Latin ''mare'', meaning sea or ocean). A habitat is an ecological or environmen ...

, as a

by consuming

provide the regulation of bacterial populations and helping in

within microbial communities. As well as its role as prey for larger microorganisms, ecologically ''Palpitomonas'' importance in maintaining

ecosystem An ecosystem (or ecological system) is a system formed by Organism, organisms in interaction with their Biophysical environment, environment. The Biotic material, biotic and abiotic components are linked together through nutrient cycles and en ...

balance in

Evolutionary role

The combination of basal features in ''Palpitomonas'', such as its linear

and ancestral cytochrome c maturation system, make it an important organism for understanding

evolutionary Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certa ...

s. Position within

and

and its early diverging lineage provide insights into the development of

, cellular structures, and other eukaryotic traits.

History

''Palpitomonas'' ''bilix'' was first described in 2010 by Yabuki et al. after being isolated from marine environments near

Palau Palau, officially the Republic of Palau, is an island country in the Micronesia subregion of Oceania in the western Pacific Ocean. The Republic of Palau consists of approximately 340 islands and is the western part of the Caroline Islands ...

. Observations of its ultrastructure and

phylogenetic analyses In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as Computational phylogenetics, phylogenetic inference. It infers the relationship among organ ...

based on multiple genes led to its classification as a novel genus within

. This discovery provided new insights into early eukaryotic diversity and clarified the

links between

and other early-diverging groups. ''Palpitomonas'' remains valuable for studying the diversity of early eukaryotic cells.

Structure

''Palpitomonas'' has several

vacuole A vacuole () is a membrane-bound organelle which is present in Plant cell, plant and Fungus, fungal Cell (biology), cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water ...

s and an extensive endoplasmic reticulum that surrounding

. Its

have lobed shape, and the

located near the

processes

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

s. The

flagellum A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

that moves actively is covered with small hair-like structures called

s. Unlike other cryptists, '' P. bilix'' does not possess

s, the ejective organelles characteristic of cryptophytes and some kathablepharids.

Life cycle

''Palpitomonas'' reproduces asexually (binary fission) by dividing into two cell. This simple method of

reproduction Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. There are two forms of reproduction: Asexual reproduction, asexual and Sexual ...

allows Palpitomonas populations to grow quickly in favorable conditions. Unlike other

s, ''Palpitomonas'' does not

reproduce sexually Sexual reproduction is a type of reproduction that involves a complex Biological life cycle, life cycle in which a gamete (haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to p ...

, which limits its genetic diversity. However, this basic life cycle reflects its ancient place in eukaryotic history and shares similarities with other early-diverging

References

{{Taxonbar, from1=Q21573564, from2=Q65072929, from3=Q92028162, from4=Q110208093, from5=Q110208102, from6=Q25707132 Flagellates Taxa described in 2010 Cryptista Cryptista genera