Nitrogen-to-phosphorus limitation shift in a polyhydroxyalkanoate-enriched mixed microbial community

Abstract

Polyhydroxyalkanoates are biodegradable polyesters considered promising alternatives to conventional plastics. To reduce costs associated with pure cultures, increasing attention has been given to mixed microbial communities and low-cost substrates. Uncoupled feeding of carbon and nutrients enables the separation of growth and polyhydroxyalkanoates accumulation phase and has been reported as a strategy to enhance process performance. While nitrogen limitation is usually applied to restrict biomass growth, phosphorus limitation has been also proposed as a relevant alternative limiting condition. This study investigates the sequential transition from nitrogen- to phosphorus-limiting conditions in a single sequential batch reactor, with emphasis on temporal process evolution and microbial community dynamics. Nitrogen limitation was associated with higher polyhydroxybutyrate accumulation than phosphorus limitation conditions. Low phosphorus availability may have been associated with intracellular phosphorus storage or retention, potentially affecting the uncoupled feeding regime, or metabolic energy redirection mechanisms that may have reduced accumulation. Filamentous polyhydroxyalkanoates-accumulating bacteria (e.g., Neomegalonema) dominated under nitrogen limitation, whereas Thauera and Paracoccus increased under phosphorus-limiting conditions.