Biology subjects

Kirzner, S.

Publications and source records attributed to Kirzner, S..

3 recordsLinked to original sources

bioRxiv2026

Virus-grazer interplay enhances virus production, particle aggregation, and trophic efficiency during infection of Prochlorococcus

Viruses and grazers are fundamental agents of mortality in the oceans, impacting phytoplankton populations and organic matter cycling. Although viruses and grazers co-occur in nature, they are typically studied in isolation in laboratory experiments, limiting our understanding of their combined ecosystem impacts. Here, using a simplified ecosystem approach, we investigated individual and combined effects of the T7-like cyanopodovirus, P-SSP7, and the protistan grazer, Paraphysomonas bandaiensis, on the abundant marine cyanobacterium, Prochlorococcus MED4, and co-occurring non-photosynthetic heterotrophic bacteria (bacteria from here on). We observed that, individually, viruses and grazers caused substantial Prochlorococcus mortality. Viral lysis also triggered increases in damaged Prochlorococcus cells, dissolved organic matter release, and bacterial growth, while grazing reduced bacterial abundances. When grazers and viruses were combined, Prochlorococcus mortality was lower than expected from the sum of their individual effects. Contrary to expectations, this reduced Prochlorococcus mortality did not result in fewer viruses or grazers. Instead, virus-grazer-Prochlorococcus interplay resulted in greater virus production, maintenance of grazer growth, and a dramatic increase in particle aggregation. Our results reveal trophic cooperation and efficiency in which competition between viruses and grazers was likely mitigated, with virus progeny production enhanced by grazers, and grazer growth sustained through a shift to alternative food sources (bacteria, damaged cells, aggregates) secondarily derived from Prochlorococcus following viral lysis. The synergistic enhancement of particle aggregation via grazer-virus-phytoplankton interplay observed with the small buoyant Prochlorococcus phytoplankter underscores the importance of food web interactions for the flow of phytoplankton-fixed carbon within, and export from, the photic zone. SignificanceViruses and grazers both use phytoplankton as a resource for reproduction. In a simplified experimental system with Prochlorococcus, an important primary producer in the oceans, we found that the interplay between viruses and grazers led to reduced mortality of Prochlorococcus. Despite this reduced mortality, virus-grazer interactions resulted in elevated virus production and a dramatic increase in organic matter aggregation. Furthermore, grazer abundance was not affected by this interplay, likely due to the transfer of organic matter from Prochlorococcus to bacteria and aggregates, which the grazers could consume as alternative food sources. These findings provide insights into the complexity of ecosystem interactions and how they impact the fate of organic matter fixed by phytoplankton in the oceans.

microbiology↗

bioRxiv2025

Inferring single-cell heterogeneity of bacteriophage life-history traits from population-scale dynamics

Phage-induced lysis of bacteria transforms population dynamics, community structure, and ecosystem functioning. Scaling up infected cell fate to quantify population- and ecosystem-scale impacts requires estimates of viral life history traits, including underlying heterogeneity in the timing, efficiency, and outcome of lytic infections. However, the variability of lysis-associated phage traits remains poorly characterized. Here, we infer single-cell heterogeneity in lysis-associated traits for an ecologically relevant system: Syn9, a T4-like cyanophage infecting Synechococcus strain WH8109, a representative of globally abundant marine cyanobacteria. We estimate the heterogeneous distribution of latent period and burst size using a nonlinear model of infection dynamics applied to population-scale time series data. We then validate our inference approach using a single-cell assay - demonstrating the feasibility of inferring phage trait heterogeneity from population data even in the absence of single-cell experiments. The variation in Syn9s latent period exceeds that previously found in coliphages and reinforces the limitations of representing viral traits with a single value. Moreover, by partitioning lytic events via the inferred heterogeneous latent period distribution, we show that realized burst size variability is largely explained by differences in latent period, providing a path forward to measure and integrate trait (co)variation into population and ecosystem models.

microbiology↗

bioRxiv2018

Adaptation to sub-optimal hosts is a driver of viral diversification in the ocean

Marine cyanophages are viruses that infect oceanic cyanobacteria, thus affecting global ecological processes. Cyanophages of the Myoviridae family are of great interest since they include generalist viruses capable of infection of a wide range of hosts including those from different cyanobacterial genera. While the influence of phages on host evolution has been studied previously, it is not known how the infection of distinct hosts influences the evolution of cyanophage populations. In marine systems this question is of special interest as the abundance of different Synechococcus and Prochlorococcus hosts constantly changes, temporally and spatially. Here, using an experimental evolution approach, we investigated the adaptation of multiple cyanophage populations to three distinct cyanobacterial hosts. We show that when infecting an \"optimal\" host, whose infection is the most efficient, phage populations accumulated only a few mutations. However, when infecting \"sub-optimal\" hosts, different, largely host-specific sets of mutations, spread in the phage populations, leading to rapid diversification into distinct subpopulations. The mutations included insertions, deletions, SNPs and codon adaptations. Most of the mutations were found in genes encoding for proteins responsible for host recognition, attachment and infection, regardless of their evolutionary conservation. Based on our results, we propose a model demonstrating how shifts in bacterial abundance, which lead to infection of \"sub-optimal\" hosts, act as a driver for rapid diversification of phage populations.

evolutionary biology↗