Enrichment of a Mixed Bacterial Culture with a High Polyhydroxyalkanoate Storage Capacity

Abstract

Polyhydroxyalkanoates (PHAs) are microbial storage polymers that attract interest as bioplastics. PHAs can be produced with open mixed cultures if a suitable enrichment step based on the ecological role of PHA is used. An acetate-fed sequencing batch reactor operated with 1 day biomass residence time and with feast-famine cycles of 12 h was used to enrich a mixed culture of PHA producers. In subsequent fed-batch experiments under growth limiting conditions, the enriched mixed culture produced PHA up to a cellular content of 89 wt % within 7.6 h (average rate of 1.2 g/g/h). The PHA produced from acetate was the homopolymer polyhydroxybutyrate. The culture was dominated by a Gammaproteobacterium that showed little similarity on 16S rRNA level with known bacteria (<90% sequence similarity). The mixed culture process for PHA production does not require aseptic conditions. Waste streams rather than pure substrates could be used as raw materials.

Ecobiotechnological Strategy to Enhance Efficiency of Bioconversion of Wastes into Hydrogen and Methane

“…Mixed defined bacteria as inoculum enhances the chance of survival of at least one or two types of bacteria, which are sufficient to ensure consistency and reproducibility of the process. This approach has been exploited previously for producing polyhydroxyalkanoates [14,18]. In the present work, the whole process is quite complex.…”

“…The ecobiotechnological strategy is based on the concept of using a mixture of bacteria, which have been well defined to carry out the desired metabolic activity. Under a given set of physiological conditions prevailing in a fermenting biowaste, at least one of these well defined bacteria will be able to survive and carry out the process successfully [14,18].…”

Composition of mixed culture PHA biopolymers and implications for downstream processing

“…In the second stage, the PHA-storing microorganisms are transferred to a nutrient limited fed-batch reactor with a high organic load maximising the polymer accumulation. PHA contents of up to 89% of the cell dry weight have been achieved in approximately 8 hours of reaction using acetate as substrate using this strategy (Johnson et al 2009). …”

“…Previous works have shown that through selection pressures, mixed cultures can be shifted into very well defined and narrow community compositions with high yielding and consistent PHA production using synthetic feeds (Johnson et al 2009. It is known that the PHA performance of a microbial population selected using waste feedstocks is influenced by the VFA composition (Duque et al 2014) and the concentration of VFA feeding the SBR (Albuquerque et al 2010).…”

“…Existing metabolic models assume that the use of acetyl-CoA and propionyl-CoA for active biomass synthesis is proportional to the acetic and propionic acid uptake ). These models are based on the metabolic approach described by van Aalst-van Leeuwen et al (1997) and are a set of empiric equations to describe volatile fatty acid uptake and polymer production (Dias et al 2005, Johnson et al 2009), and monomer composition ).…”