The C. elegans transcriptome exhibits reproducible, periodic patterns that are phase-locked with features of the larval molting cycle, but the gene regulatory networks underlying this interdependency are unknown. We show here that repeated transcriptional pulses of the lin-4 temporal patterning miRNA are generated by cooperative binding between the C. elegans orthologs of master circadian regulators Rev-Erb and ROR to elements upstream of the lin-4 gene. Remarkably, the precise timing and length of lin-4 transcriptional pulses are dictated by the phased overlap of NHR-85Rev-Erb and NHR-23ROR temporal expression patterns. We also demonstrate that LIN-42Period functions in a similar capacity to its circadian orthologs to negatively regulate periodic transcription but does so by limiting the duration of NHR-85Rev-Erb/NHR-23ROR cooperative activity at the lin-4 gene.
Microbially induced calcite precipitation (MICP) technique has gained attention recently as a novel method to enhance the engineering properties of soils, especially sandy soils. However, the applicability of this method to field scale is challenging and requires understanding of the factors affecting MICP process under variable subsurface conditions. This study presents a laboratory investigation and numerical predictive model to assess pore-water chemistry and calcite precipitation during the biocementation process. Laboratory experiments were conducted to assess the microbial treatment of Narmada sand in plastic tubes using three bacterial strains and two cementation media concentrations. Calcite precipitation via ureolysis as a result of biogeochemical reactions was measured. The effects of pH and electrical conductivity (EC) on the rate of urea hydrolysis and calcite precipitation were assessed. The presence of calcite crystals was analyzed using scanning electron microscopy (SEM). The SEM images confirmed the formation of calcite at the surface and between the sand particles. A simplified numerical model was developed to estimate the rate of urea hydrolysis and their effects on the biocementation of sand. Three stages of MICP process were identified: bacterial ureolysis, dynamic equilibrium between liquid-gas interface and oversaturation of ions, and calcite precipitation. The variations of pH and EC at these three stages were modeled. The predicted pH, EC, and calcite precipitation based on the simplified model were found to be in close agreement with the experimental results. The numerical model can be used to assess and optimize the system variables for effective MICP field applications.
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