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P. aeruginosa is a ubiquitous species found in an array of different environments, including in human and other animal hosts where they act as pathogens. Their versatility of these rod-shaped bacteria, in terms of environments they are able to occupy, is coherent with their ability to easily adapt to changing environmental factors, and draw nutrients from many different sources.

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The reasons for this adaptability and versatility are many. P. aeruginosa have larger genomes compared to other bacterium (5.5 and 7 million base pairs), due to what is called the accessory genome, large numbers of regulatory genes (including two-component regulatory systems, transporters, and transcriptional regulators), genome plasticity, and the ability to communicate with other pseudomonads and bacterium via horizontal gene transfer (these last components are also due to the variety seen in the accessory genome). P. aeruginosa is composed of a single circular core chromosome and a large and variable number of plasmids, depending on the strain. The number of plasmids are highly variable and make up the vast majority of the genomic diversity. The core genome is highly conserved amongst the different strains, representing 0.5% to 0.7% of the sequence diversity. It should also be noted that the core genome is arranged in a collinear manner and is the largest part of the genome, even though it does not confer as many different proteins and enzymes. The intra-chromosomal plasmids make up the accessory genome located at 79 different regions. These individual regions, scattered throughout the genome, differ in metabolism and confer many different proteins and enzymes that contribute to the diversity in the bacteria. The only fully sequenced P. aeruginosa genomes (four in total) are from the strains found on human skin, although the bacterium are prevalent in aquatic environments, and plant and animal surfaces. The first strand of P. aeruginosa to be entirely sequences is called PA01. This strand has a circular chromosome (6.264 million base pairs long), that encodes 5,570 protein coding sequences. PA01 has become the referecial strain to study P. aeruginosa. Most gene expression in P. aeruginosa is like any other bacteria. Transcription and translation are coupled. Transcription is initiated by the binding of RNAP (RNA polymerase) to the promoter. Then mRNA synthesis occurs (in the 5’ to 3’ direction). Transcription is then ended by either a Rho-dependent or independent terminator. In either case, the mRNA molecule is released and RNAP is removed from the DNA template. Translation is occurring almost simultaneously, by the 70S ribosomes at the start codon (AUG), after the 30S subunit binds to RBS (Ribosome Binding Site). Translation occurs from the N-terminus to the C-terminus and stops at a nonsense codon. A major difference for P. aeruginosa is that they also acquire parts of their genome from horizontal gene transfer from other stands of P. aeruginosa, other bacteria and even from phages. Horizontal transfer occurs by transmission of DNA from one organism to another. P. aeruginosa acquires genetic material from other bacteria and phages to the organism’s plasmids. This genetic material transfer accounts for a substantial part of the adapting capabilities and versatility in P. aeruginosa. Transmission is when DNA is passed from an exterior organism to gametes of another organism. For P. aeruginosa, the DNA acquired from exterior organisms is passed down in the plasmids. This allows for a large amount of diversity, without mutations occurring in the core genome, but mostly in the accessory genome.

References Bervoets, Indra, and Daniel Charlier. “Diversity, Versatility and Complexity of Bacterial Gene Regulation Mechanisms: Opportunities and Drawbacks for Applications in Synthetic Biology.” OUP Academic, Oxford University Press, 4 Feb. 2019, Klockgether, Jens, et al. “Pseudomonas Aeruginosa Genomic Structure and Diversity.” Frontiers, Frontiers, 1 Jan. 1AD, Pseudomonas aeruginosa genome (G,a variable number of plasmids.