Abstract
One of the universal traits of microorganisms is their ability to form multicellular structures, the cells of which differentiate and communicate via various signaling molecules. Reactive oxygen species (ROS), and hydrogen peroxide in particular, have recently become well-established signaling molecules in higher eukaryotes, but still little is known about the regulatory functions of ROS in microbial structures. Here we summarize current knowledge on the possible roles of ROS during the development of colonies and biofilms, representatives of microbial multicellularity. In Saccharomyces cerevisiae colonies, ROS are predicted to participate in regulatory events involved in the induction of ammonia signaling and later on in programmed cell death in the colony center. While the latter process seems to be induced by the total ROS, the former event is likely to be regulated by ROS-homeostasis, possibly H2O2-homeostasis between the cytosol and mitochondria. In Candida albicans biofilms, the predicted signaling role of ROS is linked with quorum sensing molecule farnesol that significantly affects biofilm formation. In bacterial biofilms, ROS induce genetic variability, promote cell death in specific biofilm regions, and possibly regulate biofilm development. Thus, the number of examples suggesting ROS as signaling molecules and effectors in the development of microbial multicellularity is rapidly increasing.
Highlights
Since the first observations of microorganisms by Antonie van Leeuwenhoek and their isolation and cultivation by Robert Koch, microorganisms have been traditionally viewed as simple unicellular organisms
We propose that Reactive oxygen species (ROS) are produced by the central cells in response to ammonia and/or alkalization and their production leads to cell death
Endogenous ROS production is an inevitable consequence of microbial life in the presence of oxygen and can be even potentiated by some antibiotics that induce ROS production in sensitive microbes [134,135,136]
Summary
Since the first observations of microorganisms by Antonie van Leeuwenhoek and their isolation and cultivation by Robert Koch, microorganisms have been traditionally viewed as simple unicellular organisms. The structural complexity and degree of organization of microbial multicellular structures vary from a simple single-layer biofilm and simple aggregates to complicated structures like the fruiting bodies of myxobacteria and slime molds [2, 3], complex natural biofilms [4] and the colonies of various microbes [5] Cells within these structures differentiate and use various signaling molecules to coordinate and regulate the metabolism and development of the community. In the second part of this review, we summarize current knowledge on the role of oxidative stress defense and endogenous ROS production in other well-studied microbial multicellular structures—Candida albicans and bacterial biofilms
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