Zepernick, B. N. | Search bioRxiv

bioRxiv2023

Declines in ice cover induce light limitation in freshwater diatoms

The rediscovery of diatom blooms embedded within and beneath Lake Erie ice cover (2007-2012) ignited an intense interest in psychrophilic adaptations and winter limnology. Subsequent studies determined ice plays a vital role in winter diatom ecophysiology, as diatoms partition to the underside of ice thereby fixing their location within the photic zone. Yet, climate change has led to widespread ice decline across the Great Lakes, with Lake Erie presenting a nearly ice-free state in several recent winters. It has been hypothesized the resultant turbid, isothermal water column will induce light limitation amongst winter diatoms, serving as a detrimental competitive disadvantage. Here, we conducted a physiochemical and metatranscriptomic survey of the winter Lake Erie water column (2019-2020) that spanned spatial, temporal, and climatic gradients to investigate this hypothesis. We determined ice-free conditions decreased diatom bloom magnitude and altered diatom community composition. Diatoms increased the expression of various photosynthetic genes and iron transporters, suggesting they are attempting to increase their quantity of photosystems and light-harvesting components (a well-defined indicator of light limitation). Notably, we identified two gene families which serve to increase diatom fitness in the turbid ice-free water column: proton-pumping rhodopsins (a second means of light-driven energy acquisition) and fasciclins (a means to "raft" together to increase buoyancy and co-locate to the surface to optimize light acquisition). With large-scale climatic changes already underway, our observations provide insight into how diatoms respond to the dynamic ice conditions of today and shed light on how they will fare in a climatically altered tomorrow.

ecology↗

bioRxiv2019

Flaming as part of aseptic technique increases CO2(g) and decreases pH in freshwater culture media

Aseptic technique has historically served as a fundamental practice in microbiology, helping maintain culture purity and integrity. This technique has been widely encouraged and employed for use with cultures of heterotrophic bacteria as well as freshwater and marine algae. Yet, recent observations have suggested these approaches may bring their own influences. We observed variations in growth amongst replicate experimental cyanobacterial cultures upon flaming of the culture tube opening during sample transfer and collection. Investigation revealed the pH of culture media had decreased from the initial pH established during media preparation. Flaming of sterile culture media alone confirmed a significant decrease, by as much as 1.7 pH units, and correlated with increased flaming events over time. We hypothesized that the causative factor was the introduction of carbon dioxide into the media. To test this hypothesis, qualitative and quantitative analyses were used to identify the primary driver of pH decline. We further assessed the direct effects of flaming and subsequent pH changes on Microcystis aeruginosa cultures, showing flame-driven pH changes and/or the introduction of carbon dioxide influenced experimental results. Our observations provide a cautionary tale of how classic and well-accepted approaches may not always provide the results promised, suggesting new approaches may be necessary in research areas assessing pH or carbon related-effects on microbial communities.

microbiology↗