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= Microbial biological market theory = Biological market theory elaborates on the concept of reciprocal altruism. The 'market' metaphor refers to the cooperation and exchanges that happen in ecosystems between organisms and their environment. In the same way that humans exchange commodities, microbes that can offer desired goods & services to surrounding plants will utilize mechanisms that resemble supply and demand.

The market parallel was proposed by Ronald Noë and Peter Hammerstein, due to the implications that changing supply and demand will cause exchange values of the traded commodities to fluctuate. The theory assumes no use of physical force or threat to seize commodities, as is found in human markets.

Microbes' interactions with plants are no exception to the biological market, as they have been known to assist with processes such as nutrient transfer. These interactions are often mutualistic, and involve similar exchanges to animal biological markets. Arbuscular mycorrhizal fungi, for example, provide an array of benefits to plants in exchange for allocation of carbon resources. This exchange is benefited by increased carbon supply in the atmosphere, and has been observed to allow host plants to provide more carbon to higher-quality mycorrhizae, reducing low-quality mutualist abundance.

Formal properties of biological markets
In the biological market, five properties are often met to label the market as such. These characteristics can be found in mating systems, mutualisms, and cooperation among species. Assumptions in the biological market include:


 * 1) Assets can be exchanged in the market between individuals.  The degree to which these individuals have control over these assets can influence exchange rates, supply, and demand.
 * 2) Often there will be a large selection of potential trading partners. Those that wish to exchange commodities must choose the most ideal trading partner.
 * 3) When exchanging assets, there will be competition within the market to be the best trading partner. Competition often increases the value of the commodity in question.
 * 4) Some materials being exchanged in a market will be sought after more than others, or be more scarce. This aspect introduces a 'supply & demand' element, increasing or decreasing the value of exchangeable commodities.
 * 5) When commodities are being offered, they can be advertised by the trader; sometimes even to mislead potential trading partners to believe the commodity is more valuable than it actually is.

Economic strategies of biological markets
An economic foundation can be used to further explain biological markets. There are six strategies that can be utilized in an economic market, and the concept applies similarly to microbial biological markets. Though these exchanges occur largely between microbes and their hosts, microbes also regularly interact with other microbes in similar fashion; intraspecific communication, for example. These cooperative behaviors can be analyzed with the biological market approach, though economic strategies can also make for useful parallels.

Avoid bad trading partners
Microbes & hosts alike must evaluate a trading partner's actual contribution to an interaction, and establish whether or not the trade is 'fair.' An example can be observed in client fish, and how they will seek better cleaners if they are cheated by their original cleaner fish feeding on their mucus or scales.

Build local business ties
Non-filamentous microbes don't have the benefit of the capability to initiate multiple trades with several partners simultaneously, as their filamentous counterparts have. Therefore, they must optimize their spatial structure to keep their benefactors close, while also minimizing diffusion of their own valuable resources. An example was produced with two species of bacteria - Salmonella enterica and Escherichia coli. The E. coli strain was unable to produce a specific amino acid, and the Salmonella assisted the E. coli by consuming metabolic waste. By establishing initial cooperation via the consumption of the waste, the Salmonella strain eventually was able to evolve to provide the E. coli with the amino acid that it previously was not able to utilize; though, if the spatial structure in which the two strains were cooperating in ceased, so did the cooperation.

Diversify or specialize
Microbes can also increase their success in the biological market through diversification of their commodities, especially if the diversification improves the usefulness of the microbe over a wider range of conditions in their market. A clear example can be found in leaf-cutter ants, who are hosts to a type of actinomycetous bacteria. These bacteria create antibiotics for the ants which not only protect them from Escovopsis (a parasitic microfungus), but also a broad range of other fungal infections. By diversifying the protection that they provide, the bacteria incentivize the leaf-cutter ants to act as their host.

Contrarily, when a trading partner is the source of a single commodity, they usually are favored when that good or service experiences high competition. This phenomena is likely due to the idea that when a source is specialized in one commodity, they are more 'affordable' than their competition to their trading partners. For instance, a cyanobacterium that fixes nitrogen (dubbed UCYN-A) had been discovered to completely lack an oxygen-evolving photosystem. It symbiotically exists with a single-celled prymnesiophyte, for which it provides nitrogen in exchange for carbon due to its lack of ability to photosynthesize.

Become indispensable
By monopolizing a commodity, microbes can increase their value in the biological market. Once a microbe has established its good or service as indispensable, it can perform trades of higher value because the trade partner likely needs the microbe to maintain fitness. This sort of relationship is clearly displayed organisms living in harsh, nutrient-scarce environments. An example is Olavius algarvensis, a deep sea worm that relies on endosymbiotic, chemosynthetic bacteria to provide nutrients and energy they otherwise could not produce in their environment. The host provides a habitat and protection for the bacteria, while the bacteria provide the host with essential services.

Save for a rainy day
Microbes can also display behaviors that can best be described as hoarding resources in order to redistribute them when it is most beneficial. Typically, microbes will store resources without trade only if three conditions are met: the resource must experience frequent periods of scarcity so that supply is in high demand, the microbe providing the resource must provide the best trade options, and the resource must be able to be stored. Some micorrhizal fungi will withhold phosphorus resources from hosts, or store them for later beneficial use.

Eliminate the competition
To gain advantage in the market, organisms will often act in an antagonistic way to limit valuable trade conditions for their competition. Microbes specifically are capable of producing bacteriocins which provide an advantage by inhibiting, or in some cases even killing, other bacteria. Often, bacteria will emit bacteriocins targeting similar bacteria to themselves to reduce competition for resources. Studies involving lab-produced strains of Pseudomonas aeruginosa used against a multitude of similar strains were conducted to exemplify antagonistic behavior. It was discovered that the use of bacteriocins reached maximum efficiency when the similarities between strains were in the median range - too similar, and the strains were already resistant to the bacteriocins; too different, and the strains weren't competing for the same resources.

Examples of altruism in plants & microbes
Altruism in biology refers to behavior that detriments the fitness of one individual while benefiting the fitness of another, usually genetically-related (though not always), individual. Microbes have been observed to display altruistic behavior both to host plants and other microbes. Altruism can either directly benefit another individual immediately, such as in nutrient transfers in a dying host, or indirectly benefit individuals who share genetic information (kin selection). Because microbes reproduce asexually, close genetic relatives are common, and are therefore much more likely to behave altruistically.


 * Defoliated Pseudotsuga menziesii have been observed utilizing mycorrhizal networks to transfer resources to nearby regenerating Pinus ponderosa, contributing to the revitalization of forests.
 * Mycorrhizal networks can also be used to change plant characteristics such as physiology, gene regulation and defense response. Mycorrhizae assist with a sort of communication between plants involving resource transfer or signaling defense receptors.
 * Rhizobia and legumes maintain a common symbiotic relationship in which the legumes provide the rhizobia with nutrients while the rhizobia provide the legumes with nitrogen via fixation.
 * Programmed cell death (apoptosis) in yeast, while not directly beneficial to the fitness of other individuals, could provide indirect benefits to individuals with genetic similarity.
 * E. Coli will respond to phage attacks by causing infected cells to all die together. This will prevent the parasite from spreading to future generations.
 * Dictyostelium discoideum, a slime mold, will aggregate into a multicellular organism to migrate to the surface of soil, then transforms into a stalk of spores to disperse its reproductive spores.