Scalable Production of Peptides for Enhanced Struvite Formation via Expression on the Surface of Genetically Engineered Microbes

Abstract

A promising method for recycling phosphate from wastewater is through precipitation of struvite (MgNH₄PO₄·6H₂O), a slow-release fertilizer. Peptides have been shown to increase the yield of struvite formation, but producing peptides via solid phase synthesis is cost prohibitive. This work investigates the effects of peptide-expressing bacteria on struvite precipitation to provide a sustainable and cost-efficient means to enhance struvite precipitation. A peptide known for increased struvite yield was expressed on a membrane protein in Escherichia coli(E. coli), and then 5 mL precipitation reactions were performed in 50 mL culture tubes for at least 15 min. The yield of struvite crystals was examined, with the presence of peptide-expressing E. coli inducing significantly higher yields than nonpeptide-expressing E. coli when normalized to the amount of bacteria. The precipitate was identified as struvite through Fourier transform infrared spectroscopy and energy dispersive spectroscopy, while the morphology and size of the crystals were analyzed through optical microscopy and scanning electron microscopy. Crystals were found to have a larger area when precipitated with the peptide-expressing bacteria. Additionally, bacteria–struvite samples were thermogravimetrically analyzed to quantify their purity and determine their thermal decomposition behavior. Overall, this study presents the benefits of a novel, microbe-driven method of struvite precipitation, offering a means for scalable implementation.