Abstract
Microorganisms are widely utilized for the treatment of wastewater in activated sludge systems. However, the uncontrolled growth of filamentous bacteria leads to bulking and adversely affects wastewater treatment efficiency. To clarify the nutrient requirements for filament formation, we track the growth of a filamentous bacterium, Leptothrix cholodnii SP-6 in different nutrient-limited conditions using a high aspect-ratio microfluidic chamber to follow cell-chain elongation and sheath formation. We find that limitations in Na+, K+, and Fe2+ yield no observable changes in the elongation of cell chains and sheath formation, whereas limitations of C, N, P, or vitamins lead to more pronounced changes in filament morphology; here we observe the appearance of partially empty filaments with wide intercellular gaps. We observe more dramatic differences when SP-6 cells are transferred to media lacking Mg2+ and Ca2+. Loss of Mg2+ results in cell autolysis, while removal of Ca2+ results in the catastrophic disintegration of the filaments. By simultaneously limiting both carbon and Ca2+ sources, we are able to stimulate planktonic cell generation. These findings paint a detailed picture of the ecophysiology of Leptothrix, which may lead to improved control over the unchecked growth of deleterious filamentous bacteria in water purification systems.
Highlights
Sustainable management of water resources is an issue of fundamental importance for supporting the health of growing populations and continued development of economic activity
To measure the effect of abrupt nutrient limitation on cell behavior, we culture SP-6 cells in 2D chambers that are fed with MSVP culture media that are severely depleted in specific components
We confirm that L. cholodnii cultured in full strength MSVP display behavior that is consistent with previous reports
Summary
Sustainable management of water resources is an issue of fundamental importance for supporting the health of growing populations and continued development of economic activity. In contrast to the usefulness of bacteria for industrial water filtration and wastewater treatment, filamentous bacteria such as various species of Sphaerotilus, Thiothrix, and Leptothrix, can grow exponentially, thereby forming microbial mats that clog water distribution systems and lead to bulking and/or foaming in activated sludge tanks of wastewater treatment plants (van Veen et al, 1978; Kunoh et al, 2016a; Henriet et al, 2017). As they grow, these filamentous bacteria generate woven mesh-like networks that clog pipes and reduce the efficiency of separating activated sludge flocs from the water column (Eggerichs et al, 2020). To this end, developing a fundamental understanding of the mechanism of filament formation employed by such bacteria could identify new control techniques that disrupt or inhibit this mechanism, halting growth when needed to improve the capacity and efficiency of wastewater treatment while limiting the use of toxic chemicals
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