Neobodo are diverse belonging to the eukaryotic supergroup Excavata. They are Kinetoplastids in the subclass . They are small, free-living, heterotrophic flagellates with two flagella of unequal length used to create a propulsive current for feeding.[Kirchman, D. 2008: Microbial ecology of the oceans / edited David L. Kirchman. (2nd ed.).] As members of Kinetoplastids, they have an evident kinetoplast[Tikhonenkov, D. V., Janouškovec, J., Keeling, P. J., and Mylnikov, A. P. 2016: The Morphology, Ultrastructure and SSU rRNA Gene Sequence of a New Freshwater Flagellate, Neobodo borokensis n. sp. (Kinetoplastea, Excavata). The Journal Of Eukaryotic Microbiology, 63 :220–232. DOI:10.1111/jeu.12271] There was much confusion and debate within the class Kinetoplastid and subclass Bodonidae regarding the classification of the organism, but finally the new genera Neobodo was proposed by Keith Vickerman.[Moreira, David, et al. 2004: An Updated View of Kinetoplastid Phylogeny Using Environmental Sequences and a Closer Outgroup: Proposal for a New Classification of the Class Kinetoplastea. International Journal of Systematic and Evolutionary Microbiology, 54: 1861–75. DOI:10.1099/ijs.0.63081-0] Although they are one of the most common flagellates found in freshwater, they are also able to tolerate saltwater[Morgan-Smith, D., Garrison, C. E., and Bochdansky, A. B. 2013: Mortality and survival of cultured surface-ocean flagellates under simulated deep-sea conditions. Journal of Experimental Marine Biology and Ecology, 445: 13–20. DOI: 10.1016/j.jembe.2013.03.017] Their ability to alternate between both marine and freshwater environments in many parts of the world give them a “cosmopolitan” character.
Etymology
The prefix ‘Neo-’ comes from the ancient Greek word for ‘’ which signifies 'young'. Attaching the prefix to the original bodonid species,
neobodo literally means a “new” bodonid species.
History of Knowledge
The order Neobodonida was proposed by a researcher, Keith Vickerman, based on significant characteristics that differed from the original bodonid species.
Differing characteristics included: being
phagotrophic, Polykinetoplastic/eukinetoplastic, biflagellate with usually both flagella lacking hairs, having a posterior flagellum attached to the body or free of it, and having an
cytostome.
Many
Neobodo species derived from
Bodo species, and by recognizing these differences, they were tentatively assigned to the new genus
Neobodo by adding the ‘neo’ prefix.
Through studies on the ultrastructure of
Bodo designis, researchers discovered the possession of a ‘microtubular prism’ supporting the cytostome–cytopharynx, as well as a significantly different feeding apparatus from other bodonids, thus proposing the new species as
Neobodo designis.
Through this discovery, they were proposed as the type species of the new genus
Neobodo.
have very close connections with Kinetoplastid protists. Kinetoplastid protists belong together with
euglenids and
, to the phylum
Euglenozoa, and are grouped in the class Kinetoplastea.
The name of kinetoplastid is derived from the presence of a characteristic structure called the kinetoplast which is a mass of concentrated extranuclear DNA within a mitochondrion.
In the past, kinetoplastids were classified into two major suborder groups via morphology-based taxonomic criteria: either as parasitic uniflagellate
, or biflagellate bodonids.
Originally, Vickerman proposed two families,
and Cryptobiidae, but later on re-unified all bodonids within the single family, Bodonidae.
Based on comparisons of RNA sequences and molecular phylogenetic analyses, it was suggested that the trypanosomatids also emerged from within the bodonids.
Moreover, recent research of deep-sea hydrothermal vent samples at the Mid-Atlantic Ridge and analysis via PCR amplification reported several new kinetoplastid-like sequences.
Researchers David Moreira, Purificacion Lopez-Garcıa, and Keith Vickerman analyzed the phylogeny of these kinetoplastids and found a much more stable phylogeny that supported the
monophyly of groups that typically emerged as
polyphyletic in the trees rooted using the traditional, distant outgroup sequences.
As a result, the classification of the class Kinetoplastea was divided as two new subclasses:
-
Prokinetoplastina -containing various bodonid species, and
-
Metakinetoplastina -including the Trypanosomatida and three additional new orders:
Through this process, Neobodo was created as a new genus, along with the revision of the classification of species formerly included in the genus Bodo and the amendment of the genus Parabodo.
Description
The new genus
Neobodo is characterized as solitary
phagotrophic flagellates with a single discrete eukinetoplast. They are known for having an
Cytostome and
cytopharynx supported by a prismatic rod of
.
Neobodo cells are usually elongate and Ellipse in shape and somewhat inflexible.
Along with their two flagella, they have two nearly parallel basal bodies.
Habitat and Ecology
Bodonid flagellates (class Kinetoplastea) are abundant, free-living
that occur in a wide variety of environments including freshwater, soil and marine habitats ranging from the
tropics to the
Arctic.
Neobodo is one of the most common flagellates in freshwater environments, but can also tolerate marine environments with low salinities of 3–4 ppt.
Strains of
Neobodo species isolated from different environments fall exclusively into marine and freshwater lineages.
Studies show that
Neobodo is a complex and ancient species with a major marine clade nested among older freshwater clades.
[Von Der Heyden, S., and Cavalier-Smith, T. 2005: Culturing and Environmental DNA Sequencing Uncover Hidden Kinetoplastid Biodiversity and a Major Marine Clade within Ancestrally Freshwater Neobodo Designis. International Journal of Systematic and Evolutionary Microbiology, 55: 2605–2621. DOI: 10.1099/ijs.0.63606-0] This suggests that these lineages were constrained physiologically from moving between these environments for most of their long history.
Their broad physiological tolerance enables them to easily interchange between marine and freshwater environments, which gives them a cosmopolitan characteristic and a wide ecological tolerance.
Recent evidence for
Neobodo designis suggested notable divergence between freshwater and marine strains and all strains exhibited extensive genetic diversity.
studies reported the abundance of several heterotrophic nanoflagellate groups (including bodonids) in the
euphotic zone of different marine areas.
Areas include the Mediterranean Sea,
Norwegian Sea, the
Indian Ocean and around the Antarctic Peninsula.
Throughout the numerous oceans, large fractions of small heterotrophic flagellates with few morphological features remain unidentified.
Therefore there is a high possibility that there are many bodonids among the unidentified that have not yet been studied.
Although Neobodo are surface organisms, typically found in surface waters, studies have shown their ability to tolerate deep water conditions.
Feeding
Neobodo are free-living and active microbial predators that swim around and feed on prey in aquatic ecosystems.
As free-living flagellates, they are the most important bacterivorous forms in aquatic environments.
, like other bodonids, are heterotrophic flagellates (HF) which are a very diverse and heterogeneous group of protists with a size range between 1 and 450 microns.
They play an essential role in aquatic and terrestrial food webs as major consumers of bacterial biomass.
The predator to prey size ratio limits the maximal size difference between bacteria and their predator:
Neobodo.
The marine environment presents additional constraints, imposed by the typical small size and low abundance of bacteria.
In these conditions, physical and
hydrodynamic considerations theoretically restrict Neobodo’s feeding to graze on small bacteria, typically within the
nanoplankton.
Most bacterivorous protists in the marine
pelagic zone are generally in the size range of 2–5 microns and are classified as a functional group called heterotrophic nanoflagellates.
The predominance of heterotrophic nanoflagellates as marine bacterivores has been confirmed by manipulations with size-fractionated natural assemblages and by direct observation of protists with ingested fluorescent bacteria.
More specifically,
Neobodo are interception feeders, meaning they feed on bacteria attached to surfaces/biofilms or in aggregates. They press their mouth against food and are often aided by a
pseudopod-like structure (pharynx) to detach bacteria.
Within this feeding mechanism, further variability in terms of feeding behavior and selection strategies can be observed among different species.
Practical importance
Despite the
ecological and
evolutionary significance of these organisms, many of their biological and
pathological features are currently unknown. Through metatranscriptomics using
RNA-Seq combined with field-emission microscopy the
virulence factors of a recently described genus of Neobodonida that is considered to be responsible for Ascidian Soft Tunic Syndrome (AsSTS) was revealed.
[Jang, H.B., Kim, Y. K., Del Castillo, C. S., Nho, S. W., Cha, I. S., and Park, S. B. 2012: RNA-Seq-Based Metatranscriptomic and Microscopic Investigation Reveals Novel Metalloproteases of Neobodo sp. as Potential Virulence Factors for Soft Tunic Syndrome in Halocynthia roretzi. PLoS ONE, 7(12): e52379. DOI: 10.1371/journal.pone.0052379] AsSTS is a disease of the edible
ascidian,
Halocynthia roretzi, which has done enormous damage to the Korean and Japanese
aquaculture.
AsSTS is characterized by changes in the tunic (the outermost barrier against the environment), including elasticity loss and subsequent rupture leading to thinner bundled tunic
fibers and coarser tunic matrices.
However, the
pathogenesis is unclear and is still an area of research.
List of species (or of lower taxonomic units)
Despite the considerable interest in free-living bodonids, their true
biodiversity has most likely been grossly underestimated by simple
light microscopy, as it does not differentiate most ‘species’ very well.
were used to test
Neobodo’s global distribution and genetic diversity.
The non-overlap between environmental DNA sequences and those from cultures suggests that there are hundreds, possibly thousands, of different rRNA gene sequences of free-living
Neobodo species globally.
Some of the species identified to date are:
