Flux balance modeling to predict bacterial survival during pulsed-activity events
2017
Abstract. Desert biological soil crusts (BSCs) are cyanobacteria-dominated
surface soil microbial communities common to plant interspaces in arid
environments. The capability to significantly dampen their metabolism allows
them to exist for extended periods in a desiccated dormant state that is
highly robust to environmental stresses. However, within minutes of wetting,
metabolic functions reboot, maximizing activity during infrequent permissive
periods. Microcoleus vaginatus , a primary producer within the crust
ecosystem and an early colonizer, initiates crust formation by binding
particles in the upper layer of soil via exopolysaccharides, making microbial
dominated biological soil crusts highly dependent on the viability of this
organism. Previous studies have suggested that biopolymers play a central
role in the survival of this organism by powering resuscitation, rapidly
forming compatible solutes, and fueling metabolic activity in dark, hydrated
conditions. To elucidate the mechanism of this phenomenon and provide a basis
for future modeling of BSCs, we developed a manually curated, genome-scale
metabolic model of Microcoleus vaginatus (iNJ1153). To validate this
model, gas chromatography–mass spectroscopy (GC–MS) and liquid chromatography–mass spectroscopy (LC–MS) were used to characterize the rate of
biopolymer accumulation and depletion in in hydrated Microcoleus vaginatus under light and dark conditions. Constraint-based flux balance
analysis showed agreement between model predictions and experimental reaction
fluxes. A significant amount of consumed carbon and light energy is invested
into storage molecules glycogen and polyphosphate, while β -polyhydroxybutyrate may function as a secondary resource. Pseudo-steady-state
modeling suggests that glycogen, the primary carbon source with the
fastest depletion rate, will be exhausted if M. vaginatus
experiences dark wetting events 4 times longer than light wetting events.
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