Seminar of the Department of Microbiology
Rapid evolution of marine bacteria mediated by phages
Nina Bartlau, PhD - Postdoc - Universität Wien – Centre for Microbiology and Environmental Systems Science, Division of Microbial Ecology
16.01.2025, 11:00 - Hybrid
- Join online
- or in presence: Seminarraum Biologie - Foyer (Technikerstraße 25, Viktor-Franz-Hess Haus, Parterre).
Abstract
Phages shape microbial communities through their predatory activity and potential to facilitate horizontal gene transfer. Interactions between phages and their bacterial hosts are mediated by a combination of specific attachment, and host defense as well as phage counter defense mechanisms, all of which determine whether a phage can infect a particular host. However, how these complex mechanisms play out in the wild remains poorly understood. Here we reveal phage-host dynamics in a coastal marine time series using both community metagenomics and a model system based on high resolution phage-host interactions. Daily samples obtained over 93 days revealed, as a general feature, short host blooms followed by equally short phage blooms across phylogenetically diverse bacteria. To understand such dynamics mechanistically, we characterized a bloom of Vibrio splendidus and V. cyclitrophicus and a coincident bloom of their phages using a combination of metagenomics, and bacteria and phage isolation. To assess whether phage predation exerts strong selection on the host population, we tested changes in susceptibility of bacterial isolates to phages across the bloom days by conducting a cross-infection assay with 1103 V. cyclitrophicus isolates and 76 diverse V. cyclitrophicus phages. This revealed that the fraction of bacteria to which phages could attach was always higher than the fraction in which phages could replicate, indicating that internal defenses are an important element in these dynamics. Moreover, indicating phage-driven host evolution over very short time scales, strains to which phages could attach and which could be killed increased at the beginning of the bloom, peaked in the middle, and then quickly decreased where the killed hosts dropped to a very small proportion. Metagenomic analysis showed that a diverse set of phages are involved in bacterial killing, including several prophages that were actively replicating at the onset of the bloom, overall suggesting that a phage cocktail rather than single phages plays a role in limiting the bacterial bloom.