Rhodococcus opacus is a bacterium that
has a high
tolerance to aromatic compounds and can produce significant amounts
of triacylglycerol (TAG). Here, we present iGR1773, the first genome-scale
model (GSM) of R. opacus PD630 metabolism based on
its genomic sequence and associated data. The model includes 1773
genes, 3025 reactions, and 1956 metabolites, was developed in a reproducible
manner using CarveMe, and was evaluated through Metabolic Model tests
(MEMOTE). We combine the model with two Constraint-Based Reconstruction
and Analysis (COBRA) methods that use transcriptomics data to predict
growth rates and fluxes: E-Flux2 and SPOT (Simplified Pearson Correlation
with Transcriptomic data). Growth rates are best predicted by E-Flux2.
Flux profiles are more accurately predicted by E-Flux2 than flux balance
analysis (FBA) and parsimonious FBA (pFBA), when compared to 44 central
carbon fluxes measured by 13C-Metabolic Flux Analysis (13C-MFA). Under glucose-fed conditions, E-Flux2 presents an R
2 value of 0.54, while predictions based on
pFBA had an inferior R
2 of 0.28. We attribute
this improved performance to the extra activity information provided
by the transcriptomics data. For phenol-fed metabolism, in which the
substrate first enters the TCA cycle, E-Flux2’s flux predictions
display a high R
2 of 0.96 while pFBA showed
an R
2 of 0.93. We also show that glucose
metabolism and phenol metabolism function with similar relative ATP
maintenance costs. These findings demonstrate that iGR1773 can help
the metabolic engineering community predict aromatic substrate utilization
patterns and perform computational strain design.
In this work, we demonstrate plasma-catalytic synthesis of hydrogen and
acrylonitrile (AN) from CH and N. The
process involves two steps: 1) plasma synthesis of
CH and HCN in a nominally 1:1
stoichiometric ratio with high yield up to 90% and high methane
conversion > 90%; and 2) downstream thermocatalytic
reaction of these intermediates to make AN. The effect of process
parameters on product distributions and specific energy requirements are
reported. If the catalytic conversion of
CH and HCN in the downstream
thermocatalytic step to AN were perfect, which will require further
improvements in the thermocatalytic reactor, then at the maximum output
of our 1 kW radiofrequency 13.56 MHz transformer, a specific energy
requirement of 73 kWh kgANwas determined. The
expectation is that scaling up the process to higher throughputs would
result in decreases in specific energy requirement into the predicted
economically viable range less than 10 kWh kgAN.
Rate constants for the reaction of nitrate radical (NO 3 * ) with several carboxylic acids (RCO 2 H) were measured in acetonitrile using laser flash photolysis, and found to be on the order of 10 5 -10 6 M À 1 s À 1 . No observable H/D kinetic isotope effect was observed at the carboxyl OÀ H group, α-CÀ H bond and (possibly) in the case of formic acid, the formylic CÀ H bond. This suggests that NO 3 * does not abstract hydrogen from any of these positions despite the fact that all these processes are thermodynamically favorable. Reactivity increases with increased length and/or branching of the alkyl side chain (R), and approaches, but does not quite reach, that of an alkane towards NO 3 * . The relative inertness of carboxylic acids towards NO 3 * can be explained by the polar effect.
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