A study was conducted in an attempt to determine which functional regions of a particular conjugative transfer gene (tra1) are involved in the transfer of plasmid R27 in Salmonella enterica. The R27 plasmid is of significant clinical interest because it is capable of encoding multiple-antibiotic resistance to typhoid fever. To identify functional regions responsible for conjugal transfer, an analysis by Lawley et al. [(2002). J. Bacteriol. 184:2173–2180] was conducted in which particular regions of the tra1 gene were mutated and tested for their impact on conjugation. Shown here is a map of the regions tested and believed to be involved in conjugative transfer of the plasmid. Similar coloring indicates related function. Numbers correspond to each functional region subjected to mutation analysis.

Accompanying the map is a table showing the effects of these mutations on R27 conjugation.

Effects of Mutations in Functional Regions of Transfer Region 1 (tra1) on R27 Conjugation
   R27 Mutation in     Conjugative       Relative Conjugation
         Region               Transfer                Frequency (%)
             1                          +                            100
             2                          +                            100
             3                          -                               0
             4                         +                             100
             5                         -                                0
             6                         -                                0
             7                         +                              12
             8                         -                                0
             9                         -                                0
           10                         -                                0
           11                         +                              13
           12                         -                                0
           13                         -                                0
           14                         -                                0

What general conclusions might one draw from these data? 

Key Concepts

Conjugative Transfer

Conjugative transfer is a process by which one bacterium transfers genetic material to another through direct contact. This mechanism often involves plasmids, which are small, circular DNA molecules that can carry genes, including those for antibiotic resistance. Understanding this process is crucial for analyzing how genes, such as those in the tra1 gene, facilitate the transfer of plasmids like R27 in bacteria.

Mutagenesis

Mutagenesis refers to the process of inducing mutations in an organism's DNA, which can help identify the function of specific genes. In the context of the study, targeted mutations in the tra1 gene were performed to determine which regions are essential for conjugative transfer. By observing the effects of these mutations on conjugation frequency, researchers can infer the functional importance of different gene regions.

Antibiotic Resistance

Antibiotic resistance occurs when bacteria evolve mechanisms to resist the effects of drugs that once killed them or inhibited their growth. The R27 plasmid is significant because it encodes multiple antibiotic resistance genes, making it a critical focus for understanding how resistance spreads among bacterial populations. Analyzing the conjugative transfer of such plasmids is vital for addressing public health challenges related to antibiotic-resistant infections.