Chapter 13 : Unnecessary Baggage

Abstract:

The pseudogenes must be extremely rare in bacteria compared to plants and animals because bacteria grow rapidly and have small genomes. Work was carried to develop some clever genetic tricks for identifying such "host specificity" genes in Typhi. After years of hard work, it seems that the reason for restriction of Typhi to humans was not because of the acquisition of new genes but because Typhi had mutations in many different genes scattered around the chromosome. In the mid-1990s it became possible to determine the entire sequence of bacterial genomes. The genome sequences of different types of bacteria provided surprising insights into genes not known earlier. But the most striking insights came from comparisons of the genome sequences of closely related bacteria. In contrast to Salmonella Typhimurium, the human-specific pathogen Salmonella Typhi was one of these organisms with a large number of pseudogenes. In addition, many of the pseudogenes were in parts of the genome that had been identified as containing mutations that restrict host specificity. It had to be known whether the pseudogenes are responsible for restricting Typhi to the human host or whether the accumulation of pseudogenes is simply an accident. The genome sequencing studies clearly indicated that pseudogenes occur in bacteria, and the results showed that pseudogenes can influence the host range of bacterial pathogens.