The phycosphere is a microscale mucus region that is rich in
organic matter
Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
surrounding a
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
cell. This area is high in nutrients due to extracellular waste from the phytoplankton cell and it has been suggested that
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
inhabit this area to feed on these nutrients. This high nutrient environment creates a
microbiome
A microbiome () is the community of microorganisms that can usually be found living together in any given habitat. It was defined more precisely in 1988 by Whipps ''et al.'' as "a characteristic microbial community occupying a reasonably well ...
and a diverse
food web
A food web is the natural interconnection of food chains and a graphical representation of what-eats-what in an ecological community. Another name for food web is consumer-resource system. Ecologists can broadly lump all life forms into one ...
for microbes such as
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
and
protists
A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the excl ...
. It has also been suggested that the bacterial assemblages within the phycosphere are species-specific and can vary depending on different
environmental factors.
In terms of comparison, the phycosphere in
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
has been suggested analogous to the
rhizosphere
The rhizosphere is the narrow region of soil or substrate that is directly influenced by root secretions and associated soil microorganisms known as the root microbiome. Soil pores in the rhizosphere can contain many bacteria and other microor ...
in
plants
Plants are predominantly Photosynthesis, photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all curr ...
, which is the root zone important for nutrient recycling. Both plant roots and phytoplankton exude chemicals which alter their immediate surrounds drastically – including altering the pH and oxygen levels. In terms of community construction, chemotaxis is used in both environments in order to propagate the recruitment of microbes. In the rhizosphere, chemotaxis is used by the host – the plant – to mediate the motility of the soil which allows for microbial colonization. In the phycosphere, the phytoplankton release of specific chemical exudates elicits a response from bacterial symbionts who exhibit chemotaxis signaling, thereby enabling the recruitment of microbes and subsequent colonization. The interfaces also have a few similar microbes, chemicals, and metabolites involved in the host – symbiont interactions. This includes microbes such as Rhizobium, which in the phycospheres of green algae was found to be the foremost microbe when compared to other abundant community members. Chemicals such as dimethylsuloniopropionate (DMSP) and 2,3-dihydroxypropane-1-sulfonate (DHPS) and metabolites such as sugars and amino acids are implicated in the mechanisms of action of both microbiomes.
Phytoplankton-bacteria interactions
The
microscale
The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Un ...
interactions between the
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
and
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
are complex. The phytoplankton-bacteria interactions have the potential to be
parasitism
Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted structurally to this way of lif ...
, competition or
mutualism.
Interactions between phytoplankton and bacteria in the phycosphere could be potentially important in low-nutrient regions of the ocean and an example of mutualism. In marine
ecosystems
An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...
that are low in nutrients (i.e.
oligotrophic
An oligotroph is an organism that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs, which prefer nutritionally rich environments. Oligotrophs are characterized by slow growth, low rates of ...
regions of the oceans), it could be potentially beneficial for the phytoplankton to have remineralizing
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
in the phycosphere for
nutrient
A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
recycling
Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the p ...
. It has been suggested that while the bacterial activity may be low, the
taxonomic
Taxonomy is the practice and science of categorization or classification.
A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...
diversity
Diversity, diversify, or diverse may refer to:
Business
*Diversity (business), the inclusion of people of different identities (ethnicity, gender, age) in the workforce
*Diversity marketing, marketing communication targeting diverse customers
* ...
and nutritional
diversity
Diversity, diversify, or diverse may refer to:
Business
*Diversity (business), the inclusion of people of different identities (ethnicity, gender, age) in the workforce
*Diversity marketing, marketing communication targeting diverse customers
* ...
is high. This can possibly suggest that the phytoplankton species may rely on a diverse array of bacterial interactions for recycled
nutrients
A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
in these
oligotrophic
An oligotroph is an organism that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs, which prefer nutritionally rich environments. Oligotrophs are characterized by slow growth, low rates of ...
regions and the bacteria rely on organic matter surrounding the phycosphere for a source of food.
However, bacterial-phytoplankton interactions in the phycosphere could be
parasitic
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...
. In the same low nutrient oligotrophic regions of the ocean,
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
that are
nutrient
A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
stressed may not be able to produce this protective mucus layer or its associated
antibiotics
An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention o ...
. The
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
, who are also food stressed, could kill the
phytoplankton
Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'.
Ph ...
and use it as a food substrate.
Also,
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
metabolize the
organic matter
Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
through
aerobic respiration
Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...
, which depletes oxygen from the water and can lower the
pH of the water column. If enough
organic matter
Organic matter, organic material, or natural organic matter refers to the large source of carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compounds that have c ...
is produced, the bacteria could potentially harm the phytoplankton by causing the water to become more
acidic
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
. (See also
eutrophication
Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...
).
Examples of bacteria associated with phycosphere
In reality, the actual
bacterial
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
diversity
Diversity, diversify, or diverse may refer to:
Business
*Diversity (business), the inclusion of people of different identities (ethnicity, gender, age) in the workforce
*Diversity marketing, marketing communication targeting diverse customers
* ...
of the phycosphere is extremely diverse and is dependent environmental factors, such as
turbulence
In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...
in the water (so the bacteria can attach to the mucus or the phytoplankton cell) or the concentrations of nutrients. Also, the bacteria tend to be highly specialized when associated with this region. Nevertheless, here are some examples of
bacterium
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
genera
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
associated with the phycosphere.
*
Pseudomonas
''Pseudomonas'' is a genus of Gram-negative, Gammaproteobacteria, belonging to the family Pseudomonadaceae and containing 191 described species. The members of the genus demonstrate a great deal of metabolic diversity and consequently are able ...
*
Achromobacter
''Achromobacter'' is a genus of bacteria, included in the family Alcaligenaceae in the order Burkholderiales. The cells are Gram-negative straight rods and are motile by using one to 20 peritrichous flagella. They are strictly aerobic and are fo ...
*Roseobacter
*Flavobacteraceae
*Alteromonadaceae
*Athrospira plantensis
*Terrimonas rubra
*C.vulgaris
*Sediminibacterium
*Chryseobacterium
See also
*
Biomineralization
Biomineralization, also written biomineralisation, is the process by which living organisms produce minerals, often to harden or stiffen existing tissues. Such tissues are called mineralized tissues. It is an extremely widespread phenomenon; ...
*
Hologenome theory of evolution
The hologenome theory of evolution recasts the individual animal or plant (and other multicellular organisms) as a community or a "holobiont" – the host plus all of its symbiotic microbes. Consequently, the collective genomes of the holobiont for ...
*
Marine microorganisms
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 (or microbe) is any microscopic livin ...
*
Microbial loop
The microbial loop describes a trophic pathway where, in aquatic systems, dissolved organic carbon (DOC) is returned to higher trophic levels via its incorporation into bacterial biomass, and then coupled with the classic food chain formed by phy ...
*
Microbiota
Microbiota are the range of microorganisms that may be commensal, symbiotic, or pathogenic found in and on all multicellular organisms, including plants. Microbiota include bacteria, archaea, protists, fungi, and viruses, and have been found t ...
References
{{Reflist
5. Seymour, Justin R., et al. “Zooming in on the Phycosphere: the Ecological Interface for Phytoplankton–Bacteria Relationships.” Nature Microbiology, vol. 2, no. 7, 2017, pp. 1–13., doi:10.1038/nmicrobiol.2017.65.
6. Kim, B.-H., Ramanan, R., Cho, D.-H., Oh, H.-M., & Kim, H.-S. (2014). Role of Rhizobium, a plant growth promoting bacterium, in enhancing algal biomass through mutualistic interaction. Biomass and Bioenergy, 69, 95–105. doi: 10.1016/j.biombioe.2014.07.015
7. Geng, H., & Belas, R. (2010). Molecular mechanisms underlying roseobacter–phytoplankton symbioses. Current Opinion in Biotechnology, 21(3), 332–338. doi: 10.1016/j.copbio.2010.03.013
8. Ramanan, R., Kang, Z., Kim, B.-H., Cho, D.-H., Jin, L., Oh, H.-M., & Kim, H.-S. (2015). Phycosphere bacterial diversity in green algae reveals an apparent similarity across habitats. Algal Research, 8, 140–144. doi: 10.1016/j.algal.2015.02.003
9. Scharf, B. E., Hynes, M. F., & Alexandre, G. M. (2016). Chemotaxis signaling systems in model beneficial plant–bacteria associations. Plant Molecular Biology, 90(6), 549–559. doi: 10.1007/s11103-016-0432-4
Oceanography