Bacterial conjugation, mediated mainly by conjugative plasmids such as F, represents a potential health threat through the sharing of genes for pathogenicity or antibiotic resistance. Given that more than 400 different species of bacteria coinhabit a healthy human gut and more than 200 coinhabit human skin, Francisco Dionisio [(2002) Genetics 162:1525–1532] investigated the ability of plasmids to undergo between-species conjugal transfer. The following data are presented for various species of the enterobacterial genus Escherichia. The data are presented as 'log base 10' values; for example, -2.0 would be equivalent to 10⁻² as a rate of transfer. Assume that all differences between values presented are statistically significant. Donor _ Recipient E. chrysanthemi E. blattae E. fergusonii E. coli E. chrysanthemi -2.4 -4.7 -5.8 -3.7 E. blattae -2.0 -3.4 -5.2 -3.4 E. fergusonii -3.4 -5.0 -5.8 -4.2 E. coli -1.7 -3.7 -5.3 -3.5 In what species is within-species transfer most likely? In what species pair is between-species transfer most likely?

Key Concepts

Bacterial Conjugation

Bacterial conjugation is a process of horizontal gene transfer where one bacterium transfers genetic material to another through direct contact. This transfer often involves plasmids, which are small, circular DNA molecules that can carry genes for traits such as antibiotic resistance. Understanding this mechanism is crucial for analyzing how bacteria can share beneficial or harmful traits, impacting health and disease.

Conjugative Plasmids

Conjugative plasmids are specialized plasmids that facilitate the process of conjugation by encoding the necessary machinery for DNA transfer. The F plasmid is a well-known example, allowing the donor bacterium to form a pilus that connects to the recipient. These plasmids play a significant role in the spread of antibiotic resistance and virulence factors among bacterial populations.

Statistical Significance in Data Analysis

Statistical significance indicates whether the observed differences in data are likely due to chance or represent true differences in the underlying populations. In the context of the provided data, it is stated that all differences are statistically significant, meaning that the rates of plasmid transfer between species are reliably different. This concept is essential for interpreting the results of the study and understanding the implications for gene transfer dynamics.