The Effect of Outer Space and Other Environmental Cues on Bacterial Conjugation

Bar Piscon, Eliana Pia Esposito, Boris Fichtman, Guy Samburski, Lihi Efremushkin, Shimon Amselem, Amnon Harel, Galia Rahav, Raffaele Zarrilli, Ohad Gal-Mor

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3 Scopus citations


Bacterial conjugation is one of the most abundant horizontal gene transfer (HGT) mechanisms, playing a fundamental role in prokaryote evolution. A better understanding of bacterial conjugation and its cross talk with the environment is needed for a more complete understanding of HGT mechanisms and to fight the dissemination of malicious genes between bacteria. Here, we studied the effect of outer space, microgravity, and additional key environmental cues on transfer (tra) gene expression and conjugation efficiency, using the under studied broad-host range plasmid pN3, as a model. High resolution scanning electron microscopy revealed the morphology of the pN3 conjugative pili and mating pair formation during conjugation. Using a nanosatellite carrying a miniaturized lab, we studied pN3 conjugation in outer space, and used qRT-PCR, Western blotting and mating assays to determine the effect of ground physicochemical parameters on tra gene expression and conjugation. We showed for the first time that bacterial conjugation can occur in outer space and on the ground, under microgravity-simulated conditions. Furthermore, we demonstrated that microgravity, liquid media, elevated temperature, nutrient depletion, high osmolarity and low oxygen significantly reduce pN3 conjugation. Interestingly, under some of these conditions we observed an inverse correlation between tra gene transcription and conjugation frequency and found that induction of at least traK and traL can negatively affect pN3 conjugation frequency in a dose-dependent manner. Collectively, these results uncover pN3 regulation by various environmental cues and highlight the diversity of conjugation systems and the different ways in which they may be regulated in response to abiotic signals. IMPORTANCE Bacterial conjugation is a highly ubiquitous and promiscuous process, by which a donor bacterium transfers a large portion of genetic material to a recipient cell. This mechanism of horizontal gene transfer plays an important role in bacterial evolution and in the ability of bacteria to acquire resistance to antimicrobial drugs and disinfectants. Bacterial conjugation is a complex and energy-consuming process, that is tightly regulated and largely affected by various environmental signals sensed by the bacterial cell. Comprehensive knowledge about bacterial conjugation and the ways it is affected by environmental cues is required to better understand bacterial ecology and evolution and to find new effective ways to counteract the threating dissemination of antibiotic resistance genes between bacterial populations. Moreover, characterizing this process under stress or suboptimal growth conditions such as elevated temperatures, high salinity or in the outer space, may provide insights relevant to future habitat environmental conditions.

Original languageEnglish
JournalMicrobiology spectrum
Issue number3
StatePublished - 15 Jun 2023

Bibliographical note

Publisher Copyright:
Copyright © 2023 Piscon et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license.


The authors have declared that no competing interests exist. This work was supported by the grant ARGTM (Antimicrobial Resistance Gene Transfer in Microgravity) awarded to O.G.-M. and R.Z. from the Italian ministry of Foreign Affairs and International Cooperation and the Israeli Ministry of Science, Technology and Space. The work at the Gal-Mor laboratory was supported by grant numbers: I-41-416.6-2018 from the German-Israeli Foundation for Scientific Research and Development (GIF); A128055 from the Research Cooperation Lower Saxony–Israel (The Volkswagen Foundation); and 2616/18 from the joint ISF-Broad Institute program. This work was supported also by grant from the Italian Ministry of University and Research (MUR): PRIN2017 (Grant nr. 2017SFBER to R.Z.). Electron microscopy was supported by grant 958/15 from the Israel Science Foundation to A.H.

FundersFunder number
Research Cooperation Lower Saxony–Israel
Volkswagen Foundation2616/18
German-Israeli Foundation for Scientific Research and DevelopmentA128055
Ministry of Science, Technology and SpaceI-41-416.6-2018
Ministero dell’Istruzione, dell’Università e della RicercaPRIN2017, 2017SFBER, 958/15
Israel Science Foundation
Ministero degli Affari Esteri e della Cooperazione Internazionale


    • Gram-negative bacteria
    • HGT
    • T4SS
    • conjugation
    • conjugative pili
    • environmental cues
    • microgravity
    • outer space
    • plasmid
    • tra genes


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