Microbial food web
Encyclopedia
The microbial food web refers the combined trophic
interactions among microbes in aquatic environments. These microbes include viruses, bacteria
, algae
, heterotrophic protists (such as ciliates and flagellates).
In aquatic environments, microbes constitute the base of the food web
. Single celled photosynthetic organisms such as diatoms and cyanobacteria are generally the most important primary producers in the open ocean. Many of these cells, especially cyanobacteria, are too small to be captured and consumed by small crustaceans and planktonic larva
e. Instead, these cells are consumed by phagotrophic protists which are readily consumed by larger organisms. Viruses can infect and break open bacterial cells and (to a lesser extent), planktonic algae (a.k.a phytoplankton
). Therefore, viruses in the microbial food web act to reduce the population of bacteria and, by lysing bacterial cells, release particulate and dissolved organic carbon (DOC). DOC may also be released into the environment by algal cells. One of the reasons phytoplankton release DOC termed "unbalanced growth" is when essential nutrients (e.g. nitrogen
and phosphorus
) are limiting. Therefore, carbon produced during photosynthesis is not used for the synthesis of proteins (and subsequent cell growth), but is limited due of a lack of the nutrients necessary for macromolecules. Excess photosynthate, or DOC is then released, or exuded.
The microbial loop
describes a pathway in the microbial food web where DOC is returned to higher trophic level
s via the incorporation into bacterial biomass.
Trophic level
The trophic level of an organism is the position it occupies in a food chain. The word trophic derives from the Greek τροφή referring to food or feeding. A food chain represents a succession of organisms that eat another organism and are, in turn, eaten themselves. The number of steps an organism...
interactions among microbes in aquatic environments. These microbes include viruses, bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
, heterotrophic protists (such as ciliates and flagellates).
In aquatic environments, microbes constitute the base of the food web
Food web
A food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...
. Single celled photosynthetic organisms such as diatoms and cyanobacteria are generally the most important primary producers in the open ocean. Many of these cells, especially cyanobacteria, are too small to be captured and consumed by small crustaceans and planktonic larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e. Instead, these cells are consumed by phagotrophic protists which are readily consumed by larger organisms. Viruses can infect and break open bacterial cells and (to a lesser extent), planktonic algae (a.k.a phytoplankton
Phytoplankton
Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...
). Therefore, viruses in the microbial food web act to reduce the population of bacteria and, by lysing bacterial cells, release particulate and dissolved organic carbon (DOC). DOC may also be released into the environment by algal cells. One of the reasons phytoplankton release DOC termed "unbalanced growth" is when essential nutrients (e.g. nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
and phosphorus
Phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
) are limiting. Therefore, carbon produced during photosynthesis is not used for the synthesis of proteins (and subsequent cell growth), but is limited due of a lack of the nutrients necessary for macromolecules. Excess photosynthate, or DOC is then released, or exuded.
The microbial loop
Microbial loop
The microbial loop describes a trophic pathway in the marine microbial food web where dissolved organic carbon is returned to higher trophic levels via the incorporation into bacterial biomass, and coupled with the classic food chain formed by phytoplankton-zooplankton-nekton. The term microbial...
describes a pathway in the microbial food web where DOC is returned to higher trophic level
Trophic level
The trophic level of an organism is the position it occupies in a food chain. The word trophic derives from the Greek τροφή referring to food or feeding. A food chain represents a succession of organisms that eat another organism and are, in turn, eaten themselves. The number of steps an organism...
s via the incorporation into bacterial biomass.