Biology subjects

von Emster, K.

Publications and source records attributed to von Emster, K..

3 recordsLinked to original sources

bioRxiv2025

Influence of heterotrophs on phage infection of marine picocyanobacteria

Picocyanobacteria Prochlorococcus and Synechococcus coexist with both their lytic phages and heterotrophic bacteria in the oceans. These lytic phages are a significant cause of mortality, and heterotrophic bacteria have been shown to increase the fitness of Prochlorococcus by reducing oxidative stress and cross feeding under extended darkness. Studies of Prochlorococcus-phage interactions are often done with xenic cultures as it has been historically difficult to obtain and maintain heterotroph-free cultures. Here we examine the effects of heterotrophic bacteria on phage infection in Prochlorococcus and Synechococcus by comparing phage infection dynamics in cultures with and without heterotrophs present. We found that Prochlorococcus populations resumed growth following infection only in the presence of heterotrophs, independent of phage:host or heterotroph:host ratios. In phage:host pairing with Synechococcus the outcomes varied, suggesting that the impact of heterotrophs on phage infection may be dependent on the phage:host interaction. In cases where the host recovered from phage infection, heterotrophs appeared to facilitate it both by mitigating oxidative stress and possibly supplying organic carbon sources, which may support post-infection growth. Furthermore, Prochlorococcus and Synechococcus populations that recovered from infection were resistant to phage infection when transferred to fresh media. Evidence argues against genetic change as the mechanism of resistance, suggesting that Prochlorococcus and Synechococcus populations in co-culture with heterotrophs undergo non-genetic adaptations during recovery from phage infection, likely driven by heterotroph-derived organic compounds that reshape host metabolism and confer protection against future lysis.

microbiology↗

bioRxiv2024

Emergence of metabolic coupling to the heterotroph Alteromonas promotes dark survival in Prochlorococcus

Prochlorococcus is found throughout the euphotic zone in the oligotrophic open ocean. Deep mixing and sinking while attached to particles can, however, transport Prochlorococcus cells below this sunlit zone, depriving them of light for extended periods of time. Previous work has shown that Prochlorococcus by itself cannot survive extended periods of darkness. However, when co-cultured with a heterotrophic microbe and subjected to repeated periods of extended darkness, Prochlorococcus cells develop an epigenetically inherited dark-tolerant phenotype that can survive longer periods of darkness. Here we examine the metabolic and physiological changes underlying this adaptation using co-cultures of dark-tolerant and parental strains of Prochlorococcus, each grown with the heterotroph Alteromonas under diel light:dark conditions. The relative abundance of Alteromonas was higher in dark-tolerant than parental co-cultures, while dark-tolerant Prochlorococcus cells were larger, contained less chlorophyll, and were less synchronized to the light:dark cycle. Meta-transcriptome analysis revealed that dark-tolerant co-cultures undergo a joint change, in which Prochlorococcus undergoes a relative shift from photosynthesis to respiration, while Alteromonas shifts towards using more organic acids instead of sugars. Furthermore, the transcriptome data suggested enhanced biosynthesis of amino acids and purines in dark-tolerant Prochlorococcus and enhanced degradation of these compounds in Alteromonas. Collectively, our results demonstrate that dark adaptation involves a strengthening of the metabolic coupling between Prochlorococcus and Alteromonas, presumably mediated by an enhanced, and compositionally modified, carbon exchange between the two species.

microbiology↗

bioRxiv2023

Sleep is required for neural network plasticity in the jellyfish Cassiopea

Sleep in animals plays roles that appear specific to the brain, including synaptic homeostasis [1], neurotransmitter regulation [2], cellular repair [3], memory consolidation [4], and neural plasticity [5,6]. Would any of these functions of sleep be relevant to an animal without a brain? The upside-down jellyfish Cassiopea xamachana, like other cnidarians, lacks a centralized nervous system, yet the animal sleeps [7]. By tracking the propensity of the radially spaced ganglia to initiate muscle contractions over several days we determined how neural activity changes between sleep and wake in a decentralized nervous system. Ganglia-network sleep/ wake activity patterns range from being highly specialized to a few ganglia, to being completely unspecialized. Ganglia specialization also changes over time, indicating a high degree of plasticity in the neural network. The ganglia that lead activity can persist or switch between sleep/wake transitions, signifying a level of local control of the behavioral state in a decentralized nervous system. Following sleep deprivation, ganglia usage becomes far more sleep specialized, demonstrating reduced network plasticity. Together, these findings identify a novel behavioral control system that is decentralized and yet displays temporal specialization and centralization, and show a role for sleep in maintaining neural network plasticity, revealing a conserved function of sleep in this brain-less animal.

neuroscience↗