Fig. 1.

Studies on T6SSs range from the atomic over the molecular to the organismal scale. Little over a decade since its discovery, extensive knowledge has been gained on the structural aspects of T6SSs, as well as their assembly–contraction dynamics within individual bacterial cells. T6SS functionality is typically tested using in vitro assays in which the killing of prey (often E. coli as a surrogate) is enumerated. Recently, more complex systems have been studied, such as chitin-mediated T6SS induction, which fosters horizontal gene transfer in V. cholerae, light-organ occupancy among competing V. fischeri strains (6), and T6SS-mediated commensal invasion by human pathogens. Gray shaded boxes refer to the study by Speare et al. (6). IM, inner membrane; OM, outer membrane; PG, peptidoglycan.