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.

What general conclusion(s) can be drawn from these data?

Verified step by step guidance

1. Step 1: Understand the data format and what it represents. The table shows log base 10 values of plasmid transfer rates between different Escherichia species, where each value corresponds to the rate of transfer from a donor species (columns) to a recipient species (rows). For example, a value of -2.0 means a transfer rate of 10⁻².
2. Step 2: Compare transfer rates within species (diagonal values) versus between species (off-diagonal values). Notice that the diagonal values represent transfer within the same species, while off-diagonal values represent transfer between different species.
3. Step 3: Identify patterns in transfer efficiency by looking at the magnitude of the log values. Higher (less negative) values indicate higher transfer rates. For example, compare the transfer rates from E. coli donors to various recipients and vice versa.
4. Step 4: Analyze whether plasmid transfer is generally more efficient within the same species or between different species by comparing diagonal and off-diagonal values. Also, observe if some species act as better donors or recipients overall by comparing columns and rows.
5. Step 5: Draw general conclusions about the ability of plasmids to transfer between species, such as whether interspecies transfer is common or limited, and which species pairs show the highest or lowest transfer rates, indicating potential health risks related to gene sharing.

Key Concepts

Bacterial Conjugation and Plasmid Transfer

Bacterial conjugation is a process where genetic material, often plasmids, is transferred directly from a donor to a recipient cell through cell-to-cell contact. Conjugative plasmids like the F plasmid carry genes that enable this transfer, facilitating the spread of traits such as antibiotic resistance among bacteria. Understanding conjugation is key to interpreting how genes move between species.

Logarithmic Scale for Transfer Rates

The data on plasmid transfer rates are presented as log base 10 values, meaning a value of -2 corresponds to a transfer rate of 10⁻² or 0.01. This logarithmic representation allows easier comparison of rates that vary over several orders of magnitude. Recognizing this scale is essential to accurately interpret differences in transfer efficiency between species.

Species-Specific Barriers to Plasmid Transfer

The variation in transfer rates between different Escherichia species suggests that species-specific factors influence conjugation efficiency. Lower transfer rates between certain donor-recipient pairs indicate biological barriers such as restriction-modification systems or incompatibility of conjugation machinery. This concept explains why plasmid transfer is not equally efficient across all species.