Microbial intelligence (known as bacterial intelligence) is the intelligence shown by microorganisms. This includes complex adaptive behavior shown by single cells, and altruistic or cooperative behavior in populations of like or unlike cells. It is often mediated by chemical signalling that induces physiological or behavioral changes in cells and influences colony structures. [1]
Complex cells, like protozoa or algae, show remarkable abilities to organize themselves in changing circumstances. [2] Shell-building by amoebae reveals complex discrimination and manipulative skills that are ordinarily thought to occur only in multicellular organisms.
Even bacteria can display more behavior as a population. These behaviors occur in single species populations, or mixed species populations. Examples are colonies or swarms of myxobacteria, quorum sensing, and biofilms. [1] [3]
It has been suggested that a bacterial colony loosely mimics a biological neural network. The bacteria can take inputs in form of chemical signals, process them and then produce output chemicals to signal other bacteria in the colony.
Bacteria communication and self-organization in the context of network theory has been investigated by Eshel Ben-Jacob research group at Tel Aviv University which developed a fractal model of bacterial colony and identified linguistic and social patterns in colony lifecycle. [4]
Bacterial colony optimization is an algorithm used in evolutionary computing. The algorithm is based on a lifecycle model that simulates some typical behaviors of E. coli bacteria during their whole lifecycle, including chemotaxis, communication, elimination, reproduction, and migration.
Logical circuits can be built with slime moulds. [17] Distributed systems experiments have used them to approximate motorway graphs. [18] The slime mould Physarum polycephalum is able to solve the Traveling Salesman Problem, a combinatorial test with exponentially increasing complexity, in linear time. [19]
Microbial community intelligence is found in soil ecosystems in the form of interacting adaptive behaviors and metabolisms. [20] According to Ferreira et al., "Soil microbiota has its own unique capacity to recover from change and to adapt to the present state[...] [This] capacity to recover from change and to adapt to the present state by altruistic, cooperative and co-occurring behavior is considered a key attribute of microbial community intelligence." [21]
Many bacteria that exhibit complex behaviors or coordination are heavily present in soil in the form of biofilms. [1] Micropredators that inhabit soil, including social predatory bacteria, have significant implications for its ecology. Soil biodiversity, managed in part by these micropredators, is of significant importance for carbon cycling and ecosystem functioning. [22]
The complicated interaction of microbes in the soil has been proposed as a potential carbon sink. Bioaugmentation has been suggested as a method to increase the 'intelligence' of microbial communities, that is, adding the genomes of autotrophic, carbon-fixing or nitrogen-fixing bacteria to their metagenome. [20]
Bacterial transformation is a form of microbobial intelligence that involves complex adaptive cooperative behavior. About 80 species of bacteria have so far been identified that are likely capable of transformation, including about equal numbers of Gram-positive and Gram-negative bacteria. [23]
V. cholerae has the ability to communicate strongly at the cellular level for the purpose of bacterial transformation, and this form of microbial intelligence involves cooperative quorum-sensing. [24] [25] Two different stimuli that are encountered in the small intestine, the absence of oxygen and the presence of host-produced bile salts, stimulate V. cholerae quorum sensing and thus its pathogenicity. [26] Cooperative quorum sensing, involving microbial intelligence, facilitates natural genetic transformation, a process in which extracellular DNA is taken up by (competent) V. cholerae cells. [27] V. cholerae is a bacterial pathogen that causes cholera with severe contagious diarrhea that affects millions of people globally.
S. pneumoniae uses a cooperative complex quorum sensing system, a form of microbial intelligence, for regulating the release of bacteriocins as well as for differentiating into the competent state necessary for natural genetic transformation. [28] The competent state is induced by a peptide pheromone. [29] The induction of competence results in the release of DNA from a sub-fraction of S. pneumoniae cells in the population, probably by cell lysis. Subsequently the majority of the S. pneumoniae cells that have been induced to competence act as recipients and take up the DNA that is released by the donors. [29] Natural transformation in S. pneumoniae is an adaptive form of microbial intelligence for promoting genetic recombination that appears to be similar to sex in higher organisms. [29] S. pneumoniae is responsible for the death of more than a million people yearly. [30]
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