| The Type IV Secretion System of Patescibacteria is homologous to the bacterial monoderm conjugation machinery | | The Type IV Secretion System of Patescibacteria is homologous to the bacterial monoderm conjugation machinery | María del Mar Quiñonero-Coronel, Pedro J. Cabello-Yeves, Jose M Haro-Moreno, Francisco Rodríguez-Valera, M. Pilar Garcillán-Barcia | 2025-01-23T23:00:00Z | <p><span style="color:#262626;font-family:"segoe ui semilight", "segoe ui", segoe, tahoma, helvetica, arial, sans-serif;font-size:1.15em;">Abstract</span></p><p style="margin-bottom:15px;padding:0px;border:0px;outline:0px;vertical-align:baseline;font-stretch:inherit;line-height:inherit;font-size-adjust:inherit;font-feature-settings:inherit;color:#191919;background-color:#ffffff;text-align:justify;"><span class="ms-rteFontFace-5 ms-rteFontSize-2">The Candidate Phyla Radiation, also known as <em style="margin:0px;padding:0px;border:0px;outline:0px;vertical-align:baseline;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-size-adjust:inherit;font-feature-settings:inherit;">Patescibacteria</em>, represents a vast and diverse division of bacteria that has come to light via culture-independent “omics” technologies. Their limited biosynthetic capacity, along with evidence of their growth as obligate epibionts on other bacteria, suggests a broad reliance on host organisms for their survival. Nevertheless, our understanding of the molecular mechanisms governing their metabolism and lifestyle remains limited. The Type IV Secretion System (T4SS) represents a superfamily of translocation systems with a wide range of functional roles. T4SS genes have been identified in the CPR group <em style="margin:0px;padding:0px;border:0px;outline:0px;vertical-align:baseline;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-size-adjust:inherit;font-feature-settings:inherit;">Saccharibacteria</em> as essential for their epibiotic growth. In this study, we used a comprehensive bioinformatics approach to investigate the diversity and distribution of T4SS within the <em style="margin:0px;padding:0px;border:0px;outline:0px;vertical-align:baseline;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-size-adjust:inherit;font-feature-settings:inherit;">Patescibacteria</em> lineage. The phylogenetic analysis of the T4SS signature protein VirB4 suggests that most of these proteins cluster into a distinct monophyletic group with a shared ancestry to the MPF<span style="bottom:-0.5em;margin:0px;padding:0px;border:0px;outline:0px;vertical-align:baseline;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-size-adjust:inherit;font-feature-settings:inherit;">FATA</span> class of T4SS. This class is found in the conjugative elements of <em style="margin:0px;padding:0px;border:0px;outline:0px;vertical-align:baseline;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-size-adjust:inherit;font-feature-settings:inherit;">Firmicutes</em>, <em style="margin:0px;padding:0px;border:0px;outline:0px;vertical-align:baseline;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-size-adjust:inherit;font-feature-settings:inherit;">Actinobacteria</em>, <em style="margin:0px;padding:0px;border:0px;outline:0px;vertical-align:baseline;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-size-adjust:inherit;font-feature-settings:inherit;">Tenericutes</em>, and <em style="margin:0px;padding:0px;border:0px;outline:0px;vertical-align:baseline;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-size-adjust:inherit;font-feature-settings:inherit;">Archaea</em>, indicating a possible horizontal gene transfer from these monoderm microorganisms to CPR bacteria. We identified additional T4SS components near <em style="margin:0px;padding:0px;border:0px;outline:0px;vertical-align:baseline;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-size-adjust:inherit;font-feature-settings:inherit;">virB4</em>, particularly those associated with the MPF<span style="bottom:-0.5em;margin:0px;padding:0px;border:0px;outline:0px;vertical-align:baseline;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-size-adjust:inherit;font-feature-settings:inherit;">FATA</span> class, as well as homologs of other T4SS classes, such as VirB2-like pilins, and observed their varied arrangements across different CPR phyla. The absence of a relaxase in most of these T4SS clusters suggests that the system has been co-opted for other functions in CPR bacteria. The proximity of T4SS components to the origin of replication (gene <em style="margin:0px;padding:0px;border:0px;outline:0px;vertical-align:baseline;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-size-adjust:inherit;font-feature-settings:inherit;">dnaA</em>) in some CPR suggests a potential mechanism for increased expression. The broad ubiquity of a phylogenetically distinct T4SS in CPR, combined with its chromosomal location, underscores the significance of T4SS in the biology of <em style="margin:0px;padding:0px;border:0px;outline:0px;vertical-align:baseline;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-size-adjust:inherit;font-feature-settings:inherit;">Patescibacteria</em>.<br></span></p><p><br></p> | <p>(<a href="https://www.biorxiv.org/content/10.1101/2025.01.22.634366v1">preprint, in press in Microbial Genomics)</a><br><br></p> | 478 | | |
