Shaping Reactor Microbiomes to Produce the Fuel Precursor n-Butyrate from Pretreated Cellulosic Hydrolysates

Abstract

To maximize the production of carboxylic acids with open cultures of microbial consortia (reactor microbiomes), we performed experiments to understand which factors affect the community dynamics and performance parameters. We operated six thermophilic (55 °C) bioreactors to test how the factors: (i) biomass pretreatment; (ii) bioreactor operating conditions; and (iii) bioreactor history (after perturbations during the operating period) affected total fermentation product and n-butyrate performance parameters with corn fiber as the cellulosic biomass waste. We observed a maximum total fermentation product yield of 39%, a n-butyrate yield of 23% (both on a COD basis), a maximum total fermentation production rate of 0.74 g COD l(-1) d(-1) and n-butyrate production rate of 0.47 g COD l(-1) d(-1) in bioreactors that were fed with dilute-acid pretreated corn fiber at a pH of 5.5. Pyrosequencing of 16S rRNA genes with constrained ordination and other statistical methods showed that changes in operating conditions to enable dilution of toxic carboxylic acid products, which lead to these maximum performance parameters, also altered the composition of the microbiome, and that the microbiome, in turn, affected the performance. Operating conditions are an important factor (tool for operators) to shape reactor microbiomes, but other factors, such as substrate composition after biomass pretreatment and bioreactor history are also important. Further optimization of operating conditions must relieve the toxicity of carboxylic acids at acidic bioreactor pH levels even more, and this can, for example, be accomplished by extracting the product from the bioreactor solutions.

High‐rate volatile fatty acid (VFA) production by a granular sludge process at low pH

“…This coexistence can possibly be explained by the transient presence lactate and polyglucose during the operational cycle. Transient lactic acid production was reported earlier in a similar system (Agler et al, 2012), suggesting an intrinsically higher growth rate of lactic acid bacteria on glucose. A second niche may be created by microorganisms that perform anaerobic polyglucose storage as strategy for rapid glucose uptake.…”

Comparing the inhibitory thresholds of dairy manure co-digesters after prolonged acclimation periods: Part 2 – correlations between microbiomes and environment

“…The Variance Inflation Factors (VIF) for the constraining parameters were also evaluated to determine if the constraints were redundant (VIF score>10). Redundant or non-significant parameters were discarded in an iterative process until all the constraining variables in the db-RDA were significant (p < 0.05) and non-redundant (VIF score<10) (Agler et al, 2012).…”

Production of high-concentration n-caproic acid from lactate through fermentation using a newly isolated Ruminococcaceae bacterium CPB6

“…The conversion of lactate to CA had been described in pure culture studies using Megasphaera elsdenii [15] and reactor systems [16, 17]; however, the CA production from lactate was not suitable to be considered as an effective and worthwhile approach for organic waste treatment, because the CA produced was only the negligible byproduct with low titer (<1.0 g/L) beside propionate or butyrate as the main product. Recently, we reported a unique microbiome that is predominated by Clostridium cluster IV, which can efficiently convert lactate into high level of CA as the primary product [18].…”