Abstract
Bacteriophages, viruses that infect bacteria, have re-emerged as powerful regulators of bacterial populations in natural ecosystems. Phages invade the human body, just as they do other natural environments, to such an extent that they are the most numerous group in the human virome. This was only revealed in recent metagenomic studies, despite the fact that the presence of phages in the human body was reported decades ago. The influence of the presence of phages in humans has yet to be evaluated; but as in marine environments, a clear role in the regulation of bacterial populations could be envisaged, that might have an impact on human health. Moreover, phages are excellent vehicles of genetic transfer, and they contribute to the evolution of bacterial cells in the human body by spreading and acquiring DNA horizontally. The abundance of phages in the human body does not pass unnoticed and the immune system reacts to them, although it is not clear to what extent. Finally, the presence of phages in human samples, which most of the time is not considered, can influence and bias microbiological and molecular results; and, in view of the evidences, some studies suggest that more attention needs to be paid to their interference.
Highlights
Bacteriophages were discovered in the second decade of the 20th century (Twort, 1915; D’Herelle, 1917)
A different example of the regulation of human bacterial populations by phages is observed when we look at the competition between Streptococcus pneumoniae and Staphylococcus aureus
Assuming the relative occurrence and distribution of phages throughout the human body described above, coincident with the location of their bacterial hosts, and highly plausible translocation of phage particles to other areas of the body, some reports indicate that the neglected presence of phages in human samples could have an important influence by interfering in clinical practice (Brown-Jaque et al, 2016)
Summary
Bacteriophages were discovered in the second decade of the 20th century (Twort, 1915; D’Herelle, 1917). Shared genetic content is observed when analyzing the phage and bacterial DNA fractions of the same sample (Breitbart et al, 2003; Minot et al, 2011; Colombo et al, 2016; Howe et al, 2016), including sequences belonging to CRISPR-Cas systems (Dutilh et al, 2014).
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