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1.2: Interactions with their environments

Microbiology for Earth Scientists · LibreTexts

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    From LibreTexts, under CC BY-SA 4.0, as the source states it; its equations are written in TeX, which the PDF shows typeset. This page at LibreTexts.

    Microorganisms impact the properties of their environments by driving chemical reactions forward, forming biomass, and causing minerals to dissolve and precipitate. In turn, however, environments influence what microorganisms are doing by providing chemical and physical constraints on their activities. Thus, there are two-way interactions between microorganisms and their environments (Box 1.1).

    Impacts of microorganisms on their environments are diverse. They help drive the rock cycle and serve as major controls on the composition and quality of our water resources, the abundances of greenhouse gases and oxygen in the atmosphere, the fertility of soils, and more. Microbial impacts to the environment are not just subjects of academic interest, but also societal interest. They affect the habitability of the planet and resources available to human populations.

    We can better predict these impacts for natural as well as engineered systems by understanding how environments influence microbial populations. That understanding can also be used to develop strategies to manage microbial populations to achieve favorable outcomes. Microbial biotechnology offers opportunities to generate energy, increase the sustainability and amount of food production, cleanse our water, and more (Bender et al., 2016; Blaser et al., 2016; Newsome et al., 2014). Thus, exciting opportunities can emerge from learning about both sides of the two-way interactions between microbes and their environments.

    BOX 1.1 Example Interactions

    There are countless examples of the ways that environments and microbial communities interact. However, to provide a concrete example here, we consider results from the bioreactor experiments described in Paper et al. (2021). A bioreactor is a vessel that hosts biological activity and reactions. Bioreactors can take many forms but the design used by Paper et al. (2021) was relatively simple and consisted of a serum bottle containing a solution (or aqueous medium) and some sediment (Fig. \(1.1\)).

    During the incubation, microorganisms in the bioreactors primarily survived by ‘eating’ acetate \(\left(\mathrm{CH3COO}^{-}\right)\) and respiring or ‘breathing’ ferric iron \((\mathrm{Fe(III)})\) and sulfate \(\left({\mathrm{SO}_{4}}^{2-}\right)\). But the proportions of iron and sulfate they respired varied with the pH of the aqueous medium (Fig. \(1.2\mathrm{A}\)). In bioreactors supplied with an aqueous medium that had pH 6.0, microorganisms respired two to three times more iron than sulfate. In contrast, in bioreactors with pH 7.5 medium, microorganisms respired iron and sulfate in equal proportions (reaction ratio = 1). Thus, pH influenced the proportions of iron and sulfate that were respired by microbes within the bioreactors.

    While pH influenced what reactions the microorganisms were using, those reactions in turn changed the pH of the bioreactors during the incubation. When microorganisms consume ferric iron and sulfate, their reactions also consume hydrogen ions. As such, the reactions cause the pH of the bioreactor water to increase. In the experiments by Paper et al., the amount of pH increase was directly proportional to the amount of acetate that the microbes consumed (Fig. \(1.2\)).

    Taken together, the results demonstrate that pH can influence what microorganisms are doing – in this case the proportion of iron to sulfate respiration. However, in turn, microbial activity can alter pH – here by causing it to increase. Thus, the interactions go both ways.

    Simple bioreactor design consisting of a bottle containing sediment and aqueous medium, with channels to allow unreacted fluid in and reacted fluid out.
    Figure \(1.1\): Simple bioreactor design used by Paper et al. (2021)
    https://commons.wikimedia.org/wiki/File:Serum_bottle_bioreactor.png
    A: Graph showing how the environment affects microorganisms, with the molar ratio of feric iron to sulfate reduction decreasing as the pH of the media decreases. B: Graph showing how microorganisms affect their environment, increasing the pH of their surroundings as the amount of acetate they have consumed increases.
    Figure \(1.2\): Example of the two-way interactions between microorganisms and their environment based on data from bioreactor experiments described by Paper et al. (2021). (Graph A) The pH of the environment helped steer microbial activity by affecting the proportion of iron to sulfate reduction in the experiments. (Graph B) In turn, the microbial reactions caused the pH of the bioreactor solutions to increase. Scatter points show averages for replicate reactors and lines are best-fit results of linear regressions.
    https://commons.wikimedia.org/wiki/File:Example_interactions_between_microbial_activity_and_pH.png

    This page titled 1.2: Interactions with their environments was last modified on Sun, 12 May 2024 08:22:24 GMT and is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by Matthew F Kirk via source content that was edited to the style and standards of the LibreTexts platform.