Plasmids as Key Players in Acinetobacter Adaptation

Abstract

This review briefly summarizes the data on the mechanisms of development of the adaptability of Acinetobacters to various living conditions in the environment and in the clinic. A comparative analysis of the genomes of free-living and clinical strains of A. lwoffii, as well as the genomes of A. lwoffii and A. baumannii, has been carried out. It has been shown that plasmids, both large and small, play a key role in the formation of the adaptability of Acinetobacter to their living conditions. In particular, it has been demonstrated that the plasmids of various strains of Acinetobacter differ from each other in their structure and gene composition depending on the lifestyle of their host bacteria. Plasmids of modern strains are enriched with antibiotic-resistant genes, while the content of genes involved in resistance to heavy metals and arsenic is comparable to plasmids from modern and ancient strains. It is concluded that Acinetobacter plasmids may ensure the survival of host bacteria under conditions of various types of environmental and clinical stresses. A brief overview of the main mechanisms of horizontal gene transfer on plasmids inherent in Acinetobacter strains is also given.

Keywords: accessory region; antibiotic resistance; heavy metals resistance; plasmid backbone; recombination.

Figure 1

Genome-based phylogeny of A. lwoffii. The maximum likelihood tree is based on concatenated nucleotide sequences of 847 single copy genes. * Strains isolated from samples of healthy and sick animals and humans. A. pseudolwoffii DE0136 was used to root the tree. The bootstrap values for all nodes are above 99%.

Figure 2

Plasmid pRAY* and related small plasmids.

Figure 3

Diversity and abundance of heavy metals and antibiotic-resistant genes in mega-plasmids. The number of resistant genes (color scale bar) is shown for each plasmid (rows). Plasmid names are colored according to their origin: from Homo sapiens, pets, poultry, in blue; from hospital and farm environments, including hospital sewage in red; from the environment in green.

Figure 4

The main mechanisms involved in the exchange of genetic material between plasmids, involving homologous recombination (top) or site-specific recombination depending on res sites and the action of resolvases (bottom). The res sites are indicated by colored circles in the bottom panel.