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Microbial Fencing, van afweer tot coöperatie

Bruin, D. (2013) Microbial Fencing, van afweer tot coöperatie. Bachelor's Thesis, Biology.

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Abstract In the microbial world there is strong competition for resources like nutrients for growth and reproduction. This competition is the result of limited availability of these resources. In order to maximize a cell’s individual fitness, the cell usually competes by use of two strategies, denoted Scramble Competition and/or Contest Competition, where the first is a dash for resources and the second an active struggle over dominance (Hibbing et al, 2009). Contest competition can typically be described as Microbial Fencing. Microbial Fencing is local bacterial warfare by secondary metabolites like bacteriocins. It is a collective effort, otherwise it would not be effective. This is a form of cooperative behaviour, usually done by relatives and fits Hamilton’s Rule very well (Hamilton, 1963 & 1964). Here, individual fitness is no longer maximised. Instead, Inclusive fitness, the fitness of the shared genome is maximized by investments of individual cells proportional to their relatedness. Cooperative and/or altruistic behaviour are exceptions to Contest Competition. Does this mean that the exception to Microbial Fencing is cooperative and/or altruistic behaviour? In microbes, cooperative and altruistic behaviour can be explained by Hamilton’s Rule (Hamilton, 1963 & 1964) and the Selfish Gene concept (R. Dawkins, 1976). Here, signalling of relatedness and a correlating ‘hard wired’ response are required. This system is facilitated by Green Beard Genes (R. Dawkins, 1976). These genes encode for a phenotypic trait and some-what compulsory social behaviour like cooperation to others with that trait. This system is, however, sensitive to exploitation by cheaters. Cooperative behaviour is possibly enforced by Horizontal Gene Transfer. Although Horizontal Gene Transfer increases the genomic relatedness, it is likely that this does not lead to cooperative and/or altruistic behaviour in the recipient cell. Transfer of genes that encode obligatory cooperation, however, are likely be at the basis of social behaviour. These genes are disadvantageous for the recipient cell, because cooperation and/or altruistic behaviour comes with a cost to the cell, and is therefore under selection pressure. So-called Addiction Modules can keep these obligate cooperation genes anchored in a genome. Addiction Modules together with obligate cooperation genes yield an interesting perspective in the light of the Selfish Gene concept.

Item Type: Thesis (Bachelor's Thesis)
Degree programme: Biology
Thesis type: Bachelor's Thesis
Language: Dutch
Date Deposited: 15 Feb 2018 07:53
Last Modified: 15 Feb 2018 07:53

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