Biology subjects

Morris, J. J.

Publications and source records attributed to Morris, J. J..

2 recordsLinked to original sources

bioRxiv2025

Enzymatically active exudates from Alteromonas facilitate Prochlorococcus survival in stationary phase

The cyanobacterium Prochlorococcus has a conspicuously reduced genome causing it to require help from co-existing organisms for survival under a variety of stressful conditions. In this work we demonstrated that the heterotrophic bacterium Alteromonas macleodii EZ55 facilitated the survival of Prochlorococcus MIT9312 batch co-cultures as they entered stationary phase. We further showed that exudates from both Alteromonas and Prochlorococcus were responsible for this effect. Unidentified toxic exudates of Prochlorococcus lowered the carrying capacity of Pro99 medium for axenic Prochlorococcus cells, whereas heat-labile high-molecular weight exudates of Alteromonas both removed the effect of Prochlorococcus exudates and extended the lifespan of axenic Prochlorococcus cultures. Alteromonas exudates contained a wide variety of proteins and demonstrated enzymatic activities. Some of these proteins and activities may have been packaged within extracellular membrane vesicles, which we identified within Alteromonas exudates and found capable of physically associating with Prochlorococcus cells. Many of the functionalities observed in Alteromonas exudates (e.g., increasing phosphate availability, degrading hydrogen peroxide) were consistent with leaky Black Queen processes, which are defined as services provided by one organism that benefit the entire community and favor the evolution of interdependencies in microbial communities. Therefore, we discuss the potential ramifications of such processes being packaged into vesicles as opposed to freely diffusing through the extracellular milieu.

microbiology↗

bioRxiv2018

Competition and Synergy Between Prochlorococcus and Synechococcus Under Ocean Acidification Conditions

Anthropogenic CO2 emissions are projected to lower the pH of the open ocean by 0.2 to 0.3 units over the next century. Laboratory experiments show that different phytoplankton taxa exhibit a wide variety of responses, with some strains having higher fitness under projected future conditions, and others being negatively impacted. Previous studies have suggested that Prochlorococcus and Synechococcus, the numerically dominant picophytoplankton in the oceans, have very different responses to elevated CO2 that may result in a dramatic shift in their relative abundances in future oceans. Here we show that these two genera experience faster exponential growth rates under future CO2 conditions, similar to most other cyanobacteria that have been studied. However, Prochlorococcus strains have significantly lower realized growth rates due to more extreme lag periods after exposure to fresh culture media. Surprisingly, however, Synechococcus was unable to outcompete Prochlorococcus in co-culture at elevated CO2. Under these conditions, Prochlorococcus poor response to elevated CO2 disappeared, and it showed negative frequency dependence in its relative fitness compared to Synechococcus, with a significant fitness advantage when it was initially rare. Moreover, both Synechococcus and Prochlorococcus had faster growth rates in co-culture with each other than either had in unialgal culture. We speculate that this negative frequency dependence is an outgrowth of reductive Black Queen evolution operating on both taxa that has resulted in a passively mutualistic relationship analogous to that connecting Prochlorococcus with the \"helper\" heterotrophic microbes in its environment.

microbiology↗