Bt Research 2024, Vol.15, No.3, 118-130 http://microbescipublisher.com/index.php/bt 122 Figure 2 Replicon distribution and alignment hit frequencies of marker protein sequences (Adopted from Schwengers et al., 2020) Image caption: Shown here are summed plasmid and chromosome alignment hit frequencies per marker protein sequence plotted against plasmid/chromosome hit count ratios scaled to [-1, 1]; Hue:normalized replicon distribution score values (min=-100, max=100), hit count outliers below 10-4 and above 1 are discarded for the sake of readability (Adopted from Schwengers et al., 2020) In environmental samples, plasmids play a pivotal role in the adaptation of microorganisms to various stressors, such as heavy metal contamination. Tools like PlasFlow have been developed to predict plasmid sequences in metagenomic data, revealing that plasmids constitute a significant fraction of microbial communities in contaminated environments and carry genes involved in heavy-metal homeostasis (Figure 3) (Krawczyk et al., 2018). This highlights the importance of plasmids in enabling microorganisms to thrive under adverse conditions. Moreover, large-scale analyses of plasmid relationships through gene-sharing networks have shown that plasmids from different habitats often cluster together based on their genetic content rather than their environmental origin. This suggests that horizontal gene transfer between different environments is a common occurrence, further contributing to the genetic diversity of plasmids (Tamminen et sl., 2012). 5.2 Common and unique plasmids The comparison of plasmid profiles between different bacterial isolates reveals both common and unique plasmids. For example, in a study comparing the plasmid content of clinical and commensal strains of Escherichia coli and Klebsiella pneumoniae, it was found that while some replicons were common to both populations, others were unique to either clinical or commensal strains. Specifically, replicons L, M, A/C, and N were detected only in clinical strains, whereas HI1 was found exclusively in commensal strains. Despite these differences, certain replicons, such as I1 and F, were prevalent in both populations, indicating some level of shared plasmid content across different habitats (Rodríguez-Navarro et al., 2020). The COMPASS database, which compiles a vast collection of plasmid sequences from various bacterial species, further illustrates the prevalence of multireplicon plasmids and the extensive diversity of IncF plasmids. This database has revealed that many plasmids carry multiple replicons, an adaptive mechanism that extends their host range and enhances their survival and dissemination. Notably, IncF alleles are frequently found in multireplicon plasmids, particularly in Enterobacteriaceae, underscoring their role in the widespread dissemination of these genetic elements (Douarre et al., 2020).
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