Bacteriophage specificity is impacted by interactions between bacteria.

Predators play a central role in shaping community structure, function, and stability. The degree to which bacteriophage predators (viruses that infect bacteria) evolve to be specialists with a single bacterial prey species versus generalists able to consume multiple types of prey has implications for their effect on microbial communities. The presence and abundance of multiple bacterial prey types can alter selection for phage generalists, but less is known about how interactions between prey shape predator specificity in microbial systems. Using a phenomenological mathematical model of phage and bacterial populations, we find that the dominant phage strategy depends on prey ecology. Given a fitness cost for generalism, generalist predators maintain an advantage when prey species compete, while specialists dominate when prey are obligately engaged in cross-feeding interactions. We test these predictions in a synthetic microbial community with interacting strains of Escherichia coli and Salmonella enterica by competing a generalist T5-like phage able to infect both prey against P22vir, an S. enterica-specific phage. Our experimental data conform to our modeling expectations when prey species are competing or obligately mutualistic, although our results suggest that the in vitro cost of generalism is caused by a combination of biological mechanisms not anticipated in our model. Our work demonstrates that interactions between bacteria play a role in shaping ecological selection on predator specificity in obligately lytic bacteriophages and emphasizes the diversity of ways in which fitness trade-offs can manifest. IMPORTANCE: There is significant natural diversity in how many different types of bacteria a bacteriophage can infect, but the mechanisms driving this diversity are unclear. This study uses a combination of mathematical modeling and an in vitro system consisting of Escherichia coli, Salmonella enterica, a T5-like generalist phage, and the specialist phage P22vir to highlight the connection between bacteriophage specificity and interactions between their potential microbial prey. Mathematical modeling suggests that competing bacteria tend to favor generalist bacteriophage, while bacteria that benefit each other tend to favor specialist bacteriophage. Experimental results support this general finding. The experiments also show that the optimal phage strategy is impacted by phage degradation and bacterial physiology. These findings enhance our understanding of how complex microbial communities shape selection on bacteriophage specificity, which may improve our ability to use phage to manage antibiotic-resistant microbial infections.

Undergraduates' lived experience of project-/problem-based learning in introductory biology.

Recommendations for enhancing scientific literacy, inclusivity, and the ecosystem for innovation call for transitioning from teacher-centered to learner-centered science classrooms, particularly at the introductory undergraduate level. Yet little is documented about the challenges that undergraduates perceive in such classrooms and the students' ways of navigating them. Via mixed methods, we studied undergraduates' lived experience in one form of learner-centered teaching, hybrid project-/problem-based learning (PBL), in introductory organismal biology at a baccalaureate institution. Prominent in qualitative analyses of student interviews and written reflections were undergraduates' initial expectation of and longing for an emphasis on facts and transmission of them. The prominence diminished from semester's middle to end, as students came to value developing ideas, solving problems collaboratively, and engaging in deep ways of learning. Collaboration and personal resources such as belief in self emerged as supports for these shifts. Quantitative analyses corroborated that PBL students transformed as learners, moving toward informed views on the nature of science, advancing in multivariable causal reasoning, and more frequently adopting deep approaches for learning than students in lecture-based sections. The qualitative and quantitative findings portray the PBL classroom as an intercultural experience in which culture shock yields over time to acceptance in a way supported by students' internal resources and peer collaboration. The findings have value to those seeking to implement PBL and other complex-learning approaches in a manner responsive to the lived experience of the learner.