Polyhydroxybutyrate production from lactate using a mixed microbial culture

Abstract

In this study we investigated the use of lactate and a lactate/acetate mixture for enrichment of poly-3-hydroxybutyrate (PHB) producing mixed cultures. The mixed cultures were enriched in sequencing batch reactors (SBR) that established a feast-famine regime. The SBRs were operated under conditions that were previously shown to enable enrichment of a superior PHB producing strain on acetate (i.e., 12 h cycle length, 1 day SRT and 30°C). Two new mixed cultures were eventually enriched from activated sludge. The mixed culture enriched on lactate was dominated by a novel gammaproteobacterium. This enrichment can accumulate over 90 wt% PHB within 6 h, which is currently the best result reported for a bacterial culture in terms of the final PHB content and the biomass specific PHB production rate. The second mixed culture enriched on a mixture of acetate and lactate can produce up to 84 wt% PHB in just over 8 h. The predominant bacterial species in this culture were Plasticicumulans acidivorans and Thauera selenatis, which have both been reported to accumulate large amounts of PHB. The data suggest that P. acidivorans is a specialist on acetate conversion, whereas Thauera sp. is a specialist on lactate conversion. The main conclusion of this work is that the use of different substrates has a direct impact on microbial composition, but has no significant effect on the functionality of PHB production process.

Combining the enrichment and accumulation step in non-axenic PHA production: Cultivation of Plasticicumulans acidivorans at high volume exchange ratios

“…In previous acetate-fed SBRs that were dominated by P. acidivorans and operated at volume exchange ratios between 0.04 and 0.50 (1-12 h cycles) the feast phase occupied around 5% of the total cycle ( Fig. 7) (Jiang et al, 2011a(Jiang et al, , 2011b. At an exchange ratio of 0.75 (18 h cycles) the relative feast phase length increased to 12%.…”

“…Johnson et al (2009a) presented three accumulation experiments -conducted after respectively 2, 7, and 16 months of operation -that show a clear increase of the biomass-specific PHB production rate and the PHB storage capacity over time. Furthermore, the feast phase was reported to last 50 min (Johnson et al, 2009a), while later a feast phase length of 38 min has been reported for the same enrichment culture (Jiang et al, 2011b).…”

“…acidivorans predominated enrichment cultures (88-89 wt%) by, e.g., Johnson et al (2009a) and Jiang et al (2011b). The maximum PHB content reached in the culture enriched at 20 h cycles was further reduced: 83±1 wt% after 11 h or more.…”

“…Biomass with PHA contents of 70-80 wt% has thus been produced from fermented waste streams like molasses and paper or food industry effluents (Albuquerque et al, 2010;Jiang et al, 2012;Tamis et al, 2014). The highest PHA contents reported for microbial enrichment cultures are around 90 wt% and were obtained using sole acetate or lactate as substrate (Jiang et al, 2011b;Johnson et al, 2009a).…”

“…The reactor was operated for almost 4 years and cleaned once or twice a week to remove biofilm from the walls, electrodes, and other submerged reactor parts. The performance was monitored online by the length of the feast phase, which can be derived from the dissolved oxygen profile (Jiang et al, 2011b).…”