Kinetic analysis of the growth of Chlorella vulgaris

The energy of the total transmitted light was subtracted from that of the incident light in a culture vessel and the difference was divided by the weight of cells. The value thus obtained was defined as the amount, E(x), of light energy absorbed per unit cell weight per unit time.Batch and continuous cultures of Chlorella vulgaris were carried out at 30 degrees C in the pH range of 6.4-6.7 while restricting illumination. Next the specific growth rate, mu, in the batch culture and the fixed dilution rate, D, in the continuous culture were plotted against E(x). The results showed that the relation between D and E(x) can be expressed in a Michaelis-Menten equation, where the maximal specific growth rate is 0.24 h (-1) and the saturation constant is 6.58 kcal/g . h.Cell concentration calculated by substituting the apparent concentration, X(e), of incubated cells and the apparent maintenance constant, M(e), for this equation agreed with that observed in almost all growth phases. Furthermore, from the change of chlorophyll productivity and the relationship between D and E(x) expressed in this equation, it is assumed that E(x) involves the light energy directly utilized in photosynthesis in the cells and that which is converted into, e.g., heat. This equation also indicated that a maximum in the growth yield existed. Then the growth yield of 0.029 g/kcal obtained at the incident light of 1.46 or 2.63 cal/cm(2) . h was maximum (maximal conversion efficiency of light energy, 15.6%).These results indicate that this method of deriving the equation for the growth rate from this study is a useful procedure for obtaining bioengineering findings.     

Yield Coefficients of Thiobacillus neapolitanus in Continuous Culture

Thiobacillus neapolitanus, when grown in continuous culture with thiosulfate limiting growth, possessed an apparent maximal molar growth yield of 8.0 g (dry weight) per mole of thiosulfate. The substrate requirement for energy of maintenance was the highest yet reported, amounting to 21.8 mmoles of thiosulfate per g per hr. The molar growth yield, corrected for this maintenance energy requirement, was 13.9 g (dry weight) per mole of thiosulfate. It was concluded that substrate-level phosphorylation during sulfite oxidation accounted for about 45% of the adenosine triphosphate (ATP) requirement for CO₂ assimilation and maintenance during growth on limiting thiosulfate, that three sites of energy conservation exist in the electron-transport chain terminating in oxygen, and that 7.8 moles of ATP are required to fix and assimilate 1 mole of CO₂ into cell material.     

Glucose degradation, molar growth yields, and evidence for oxidative phosphorylation in Streptococcus agalactiae

In a complex medium with the energy source as the limiting nutrient factor and under anaerobic growth conditions, Streptococcus agalactiae fermented 75% of the glucose to lactic acid and the remainder to acetic and formic acids and ethanol. By using the adenosine triphosphate (ATP) yield constant of 10.5, the molar growth yield suggested 2 moles of ATP per mole of glucose from substrate level phosphorylation. Under similar growth conditions, pyruvate was fermented 25% to lactic acid, and the remainder was fermented to acetic and formic acids. The molar growth yield suggested 0.75 mole of ATP per mole of pyruvate from substrate level phosphorylation. Under aerobic growth conditions about 1 mole of oxygen was consumed per mole of glucose; about one-third of the glucose was converted to lactic acid and the remainder to acetic acid, acetoin, and carbon dioxide. Molar growth yields indicated 5 moles of ATP per mole of glucose. Estimates based on products of glucose degradation suggested that about one-half of the ATP was derived from substrate level phosphorylation and one-half from oxidative phosphorylation. Addition of 0.5 m 2,4-dinitrophenol reduced the growth yield to that occurring in the absence of oxygen. Aerobic pyruvate degradation resulted in 30% of the substrate becoming reduced to lactic acid and the remainder being converted to acetic acid and carbon dioxide, with small amounts of formic acid and acetoin. The molar growth yields and products found suggested that 0.70 mole of ATP per mole of pyruvate resulted from substrate level phosphorylation and 0.4 mole per mole of pyruvate resulted from oxidative phosphorylation.     

Energies of Activation and Uncoupled Growth in Streptococcus faecalis and Zymomonas mobilis

Growing cultures of Streptococcus faecalis at temperatures above 30 C have activation energies for both rates of growth and glycolysis of 10.3 kcal mole(-1), and a constant growth yield; when growth takes place below this temperature, the growth yield decreases and the activation energy for growth increases to 21.1 kcal mole(-1), but the activation energy for glycolysis is unchanged. The adenosine triphosphate pool in the organisms behaves differently above and below 30 C, suggesting that the energetic coupling between anabolism and catabolism is less effective below 30 C. Washed suspensions of S. faecalis have repressed glycolytic activity and an activation energy for glycolysis of 15.6 kcal mole(-1) over the whole temperature range studied. Growing cultures of Zymomonas mobilis below 33 C have a constant growth yield of 8.3 g (dry weight) of organisms per mole of glucose degraded, and activation energies for both glycolysis and growth of 11.1 kcal mole(-1); above this temperature, the growth yield falls, the activation energy for growth changes to -6.9 kcal mole(-1), but the activation energy for glycolysis is unchanged, so that the coupling between anabolism and catabolism is less effective above 33 C. The findings support the view that energy turnover in these bacteria is not well regulated.     

Growth yields of bacteria on selected organic compounds

Cell yields were determined for two bacterial soil isolants grown aerobically in minimal media on a variety of synthetic organic compounds. 1-Dodecanol, benzoic acid, phenylacetic acid, phenylglyoxylic acid, and diethylene, triethylene, and tetraethylene glycols were tested. Two “biochemicals,” succinate and acetate, were also tested for comparison. Yields were calculated on the basis of grams of cells obtained per mole of substrate utilized, gram atom of carbon utilized, mole of oxygen consumed, and equivalent of “available electrons” in the substrates. This latter value appears to be nearly constant at 3 g of cells per equivalent of “available electrons.” Yields predicted on this basis for other bacteria and for yeasts on other substrates are in fair agreement with reported values.     

Molar Growth Yields as Evidence for Oxidative Phosphorylation in Streptococcus faecalis Strain 10C1

During the aerobic growth of Streptococcus faecalis strain 10C1, with limiting levels of glucose as the substrate, a molar growth yield (Y) of 58.2 g (dry weight) per mole of glucose was obtained. Under these conditions of growth, glucose was dissimilated primarily to acetate and CO(2). The incorporation of (14)C-glucose into cell material was no greater under aerobic conditions than during anaerobic growth. Assuming an adenosine triphosphate coefficient of 10.5, the aerobic Y cannot be explained solely on the basis of substrate phosphorylation and would appear to substantiate previous enzymatic evidence for oxidative phosphorylation in this cytochromeless species. With mannitol as the substrate, an aerobic Y of 64.6 was obtained. Extracts of mannitol-grown cells contained a nicotinamide adenine dinucleotide (NAD)-linked mannitol-1-phosphate (M-1-P) dehydrogenase. The difference in aerobic Y values with mannitol and glucose as substrates would indicate that the in vivo P/O ratio from the oxidation of reduced NAD generated by the oxidation of M-1-P approximates 0.6. The Y values with pyruvate and glycerol as substrates under aerobic conditions were 15.5 and 24.7, respectively.     

Energetics of Microbacterium thermosphactum in glucose-limited continuous culture.

Microbacterium thermosphactum was grown at 25 degrees C in glucose-limited continuous culture under aerobic (greater than 120 microM oxygen) and anaerobic (less than 0.2 microM oxygen) conditions. The end products of the anaerobic metabolism of glucose were identified as L-lactate and ethanol. Together these compounds accounted for between 85 and 90% of the glucose utilized over the full range of growth rates studied. In addition, 4% of the glucose utilized was incorporated into cellular material. Under anaerobic conditions the molar growth yield was 40 g (dry weight) of cells per mol of glucose utilized, and the maintenance energy coefficient was 0.4 mmol of glucose utilized per g (dry weight) of cells per h. For cells grown under aerobic conditions in the corresponding values were 73 g/mol and 0.2 mmol/g per h, respectively. The molar growth yield with respect to adenosine 5'-triphosphate varied with the growth rate of the culture, and the true molar growth yield with respect to adenosine 5'-triphosphate was found to be 20 g/mol of adenosine 5'-triphosphate.     

Energetics of Microbacterium thermosphactum in glucose-limited continuous culture.

Microbacterium thermosphactum was grown at 25 degrees C in glucose-limited continuous culture under aerobic (greater than 120 microM oxygen) and anaerobic (less than 0.2 microM oxygen) conditions. The end products of the anaerobic metabolism of glucose were identified as L-lactate and ethanol. Together these compounds accounted for between 85 and 90% of the glucose utilized over the full range of growth rates studied. In addition, 4% of the glucose utilized was incorporated into cellular material. Under anaerobic conditions the molar growth yield was 40 g (dry weight) of cells per mol of glucose utilized, and the maintenance energy coefficient was 0.4 mmol of glucose utilized per g (dry weight) of cells per h. For cells grown under aerobic conditions in the corresponding values were 73 g/mol and 0.2 mmol/g per h, respectively. The molar growth yield with respect to adenosine 5'-triphosphate varied with the growth rate of the culture, and the true molar growth yield with respect to adenosine 5'-triphosphate was found to be 20 g/mol of adenosine 5'-triphosphate.     

Effects of growth temperature on yield and maintenance during glucose-limited continuous culture of Escherichia coli.

The effects of growth temperature on the aerobic growth yield with respect to oxygen consumption (Y0-grams [dry weight] per gram-atom of O) and the rate of maintenance respiration (m0-milligram-atoms of O/gram [dry weight] per hour) are reported for Escherichia coli B cultivated continuously in the presence of oxygen with limiting glucose. During anaerobic continuous culture, YATP(max) (grams [dry weight] per mole of ATP corrected for maintenance) increases from 10.3 to 12.7 as the growth temperature is lowered from 37 to 25 C. Over this same range, Y0(max) (Y0 corrected for maintenance respiration) rises from 12.5 to 28.8 and remains at the higher value down to 17.5 C. From 37 to 32 C, m0 increases from 0.9 to 4.4 but then falls to 1.5 as the temperature is lowered to 17.5 C. The value of m0 sharply rises some 13-fold as the temperature is raised to 42 C without a significant change in the value of Y0(max). Changes of Y0(max) are consistent with a temperature-sensitive doubling of the efficiency of oxidative phosphorylation, but the reasons for the changes of the rate of maintenance respiration are not known.     

Eukaryotic and prokaryotic DNA-polymerase. II. The role of internucleotide phosphate groups of a template in its binding with the enzyme

The affinity of different ligands (phosphate, nucleoside monophosphates, oligonucleotides) to the template binding site of DNA polymerase alpha from human placenta was estimated. To this goal, dependences of rate of the enzyme inactivation by the affinity reagent d(pT)2pC[Pt2+(NH3)2OH](pT)7 on the concentration of these ligands as competitive inhibitors were determined. Minimal ligands capable to bind with the template site of DNA polymerase alpha were shown to be triethylphosphate (Kd 600 microM) and phosphate (Kd 53 microM). Ligand affinity increases by the factor 1.71 per added monomer unit from phosphate to d(pT) and then for oligothymidylates d(Tp)nT (n 1 to 14). The partial ethylation of phosphodiester groups does not change the efficiency of the oligothymidylate binding with the enzyme. However, the complete ethylation of these groups lowers affinity of the oligothymidylates to the enzyme by 7-9 times. The decrease is comparable with the change of Pt2+-decathymidylate affinity to the enzyme caused by Mn2+-ions. The data obtained led to suggestion that an electrostatic contact (most likely, Me2+-dependent) of phosphodiester group with the enzyme takes place. The type of contact is confirmed by Gibbs' energy change 1.1-1.4 kcal/mole. Formation of a hydrogen bond with the oxygen atom of P = O group of the same phosphate is also assumed (delta G =--4.4 . . .--4.5 kcal/mole). The other internucleotide phosphates and all bases of oligonucleotides form neither hydrogen bonds nor electrostatic contacts with the template binding site. Gibbs' energy changes by 0.32 kcal/mole when the template is lengthened by one unit. We suppose that this value characterizes the energy gain in the transition of oligonucleotide template from aquous medium to the hydrophobic environement of the enzyme active site. Comparison of Km values of oligothymidylates and their partially or completely ethylated analogues as templates in the reaction of DNA polymerization catalysed by DNA polymerase alpha from human placenta and Klenow's fragment of E. coli DNA polymerase I suggests a similar mechanism of template recognition by both enzymes.     

Prediction of DNA structure from sequence: a build-up technique

A build-up technique has been devised that permits prediction of DNA structure from sequence. No experimental information is employed other than the force field parameters. This strategy for dealing with the multiple minimum problem requires a supercomputer to make the necessary global searches. The number of energy minimization trials that were made for each of the 16 deoxydinucleoside monophosphate conformational building blocks of DNA was 1944. As a test case, the minimum energy conformations of d(GpC) and d(CpG) to 5.5 kcal/mole were then combined to generate energy-minimized structures for d(CpGpC). The number of trials that were made for d(CpGpC) was 3752. Minima for this single-stranded trimer to 15 kcal/mole were then employed to search for minimum energy conformations of the duplex d(CpGpC).d(GpCpG). The number of starting conformations that were utilized at this stage was 1514. The lowest energy duplex had a Z-II-DNA conformation, followed by a B-DNA form at 1.2 kcal/mole. The A- and Z-I-forms as well as many novel Watson-Crick base-paired structures were found at higher energy. Finally, energy-minimized structures of d(CG)6.d(CG)6 in Z-II and B-DNA conformations were computed using torsion angles from the analogous duplex trimer minima.     

The reduction of xylose to xylitol by Candida guilliermondii and Candida parapsilosis: Incidence of oxygen and pH

Summary The ability of C. guilliermondii and C. parapsilosis to ferment xylose to xylitol was evaluated under different oxygen transfer rates in order to enhance the xylitol yield. In C. guilliermondii, a maximal xylitol yield of 0.66 g/g was obtained when oxygen transfer rate was 2.2 mmol/l.h. Optimal conditions to produce xylitol by C. parapsilosis (0.75 g/g) arose from cultures at pH 4.75 with 0.4 mmoles of oxygen/l.h. The response of the yeasts to anaerobic conditions has shown that oxygen was required for xylose metabolism.Nomenclature max maximum specific growth rate (per hour) - qSmax maximum specific rate of xylose consumption (g xylose per g dry biomass per hour) - qpmax maximum specific productivity of xylitol (g xylitol per g dry biomass per hour) - Qp average volumetric productivity of xylitol (g xylitol per liter per hour) - Y_P/S xylitol yield (g xylitol per g substrate utilized) - Y_P'/S glycerol yield (g glycerol per g substrate utilized) - Y_X/S biomass yield (g dry biomass per g substrate utilized)     

Energetic studies of lactose active transport in Escherichia coli membrane vesicles

The energetics of D-lactate-driven active transport of lactose in right-side-out Escherichia coli membrane vesicles has been investigated with a microcalorimetric method. Changes of enthalpy (delta Hox), free energy (delta Gox), and entropy (delta Sox) during the D-lactate oxidation reaction in the presence of membrane vesicles are -39.9 kcal, -46.4 kcal, and 22 cal/deg per mole of D-lactate, respectively. The free energy released by this reaction is utilized to form a proton electrochemical potential (delta-microH+) across the membrane. The higher observed heat in the D-lactate oxidation reaction in the presence of carbonylcyanide m-chlorophenylhydrazone (a proton ionophore) supports the postulate that delta-microH+ is formed across the membrane vesicles. Thermodynamic quantities for the formation of delta-microH+ are delta Hm = 14.1 kcal, delta Gm = 0.6 kcal, and delta Sm = 45 cal/deg per mole of D-lactate. The efficiency in the free energy transfer from the oxidation reaction to the formation of delta-microH+ (defined by delta Gm/delta Gox) was 2%, as compared to that in the heat transfer (defined by delta Hm/delta Hox) of 35%. The energetics of the movement of lactose in symport with proton across the membrane as a consequence of the formation of delta-microH+ are delta H1 = -19 kcal, delta G1 = -0.5 kcal, and delta S1 = -62 cal/deg per mole of lactose. No heat of reaction is contributed by lactose movement across the membrane without symport with H+.     

多变鱼腥藻在不同氮源培养条件下光能转换效率的研究

依公式PE=KY,其中K等于生物量的热值(每克干重千卡),Y等于产率即每吸收千卡光能所产生的生物量的干重,测试了在无氮和有结合氮培养下的多变鱼腥藻(Anabaena variabilis)的光能转化效率。结果指出在无氮培养下的最高PEN2为8．1％,在结合氮(NH4Cl)培养下PENH =4+为5.8％。对这种差异性作了简要讨论。     

Amide isosteres of lexitropsins: synthesis, DNA binding characteristics and sequence selectivity of thioformyldistamycin.

The synthesis and properties of an amide isostere of the antibiotic distamycin, thioformyldistamycin 3 is described. Compound 3 exists predominantly in the E conformation of the thioamide group in freshly prepared DMSO solution but is converted into the Z form, predicted by molecular mechanics to be more stable, on standing for 24 h. The coalescence temperature in DMSO is 110 degrees C by 1H-NMR. The thioformyl moiety of 3 is resistant to both peptidase action and acid treatment. Complementary strand MPE footprinting on a EcoRI/Hind III restriction fragment of pBR322 DNA demonstrated that either E or Z forms of 3 give a single set of footprints very similar to that of the parent antibiotic with strongest protection at TAAG and TATTAT with moderately strong protection at ATTT and AAAA. The strength of binding of 3 and distamycin from delta Tm measurements to either poly.d(AT) or calf thymus DNA is comparable. Molecular modeling predicted a preferred conformation for 3 wherein the C = S bond has a torsional angle of 110 degrees with the pyrrole ring. The energy difference between this conformation and the E form is less than 1 kcal/mole. In contrast the E-form has an energy 17.3 kcal/mole greater than the Z and a value of 26.3 kcal/mole was calculated for the energy barrier between the two isomers.     

Klenow fragment of DNA-polymerase I from E. coli. III. The role of internucleotide phosphate groups of the matrix in its binding with the enzyme

The modification of Klenow fragment of DNA polymerase I E. coli was investigated by the affinity reagents d(Tp)2C[Pt2+(NH3)2OH](pT)7 and d(pT)2pC[Pt2+(NH3)2OH](pT)7. The template binding site of the enzyme was modified by these reagents in the presence of NaF (5 mM), which inhibits selectively the 3'----5'-exonuclease activity of the enzyme and therefore prevents the reagent from degradation. NaCN destroyed covalent bonds between reagents and enzyme, restoring activity of the Klenow fragment. The affinity of different ligands (inorganic phosphate, nucleoside monophosphates, oligonucleotides) to the template binding site of Klenow fragment was estimated. Minimal ligands capable to bind with the template site were shown to be triethylphosphate (Kd 290 microM) and phosphate (Kd 26 microM). Ligand affinity increases by the factor 1.76 per an added (monomer unit from phosphate to d(pT) and then for oligonucleotides d(Tp)nT (n 1 to 19-20). At n greater than 19-20, the ligand affinity remained constant. The complete ethylation of phosphodiester groups lowers affinity of the oligothymidylates to the enzyme by approximately 10 times, and comparable decrease of Pt2+-oligonucleotide affinity to polymerase is caused by the absence of Mn2+-ions. The data obtained led to suggestion that one Me2+-dependent electrostatic contact of the template phosphodiester group with the enzyme takes place (delta G = -1.45...-1.75 kcal/mole). Formation of a hydrogen bond with the oxygen atom of P = O group of the same template phosphate is also assumed (delta G = -4.8...-4.9 kcal/mole). Other template internucleotide phosphates do not interact with the enzyme but the bases of oligonucleotides take part in hydrophobic interactions with the template binding site. Gibbs energy changes by -0.34 kcal/mole when the template is lengthened by one unit.     

多变鱼腥藻在不同氮源培养条件下光能转换效率的研究

依公式PE=KY,其中K等于生物量的热值(每克干重千卡),Y等于产率即每吸收千卡光能所产生的生物量的干重,测试了在无氮和有结合氮培养下的多变鱼腥藻(Anabaena variabilis)的光能转化效率。结果指出在无氮培养下的最高PE_(N2)为8.1%,在结合氮(NH_4Cl)培养下PE_(NH_4~ )为5.8%。对这种差异性作了简要讨论。     

Influence of transport energization on the growth yield of Escherichia coli.

The growth yields of Escherichia coli on glucose, lactose, galactose, maltose, maltotriose, and maltohexaose were estimated under anaerobic conditions in the absence of electron acceptors. The yields on these substrates exhibited significant differences when measured in carbon-limited chemostats at similar growth rates and compared in terms of grams (dry weight) of cells produced per mole of hexose utilized. Maltohexaose was the most efficiently utilized substrate, and galactose was the least efficiently utilized under these conditions. All these sugars were known to be metabolized to glucose 6-phosphate and produced the same pattern of fermentation products. The differences in growth yields were ascribed to differences in energy costs for transport and phosphorylation of these sugars. A formalized treatment of these factors in determining growth yields was established and used to obtain values for the cost of transport and hence the energy-coupling stoichiometries for the transport of substrates via proton symport and binding-protein-dependent mechanisms in vivo. By this approach, the proton-lactose stoichiometry was found to be 1.1 to 1.8 H+ per lactose, equivalent to approximately 0.5 ATP used per lactose transported. The cost of transporting maltose via a binding-protein-dependent mechanism was considerably higher, being over 1 to 1.2 ATP per maltose or maltodextrin transported. The formalized treatment also permitted estimation of the net ATP yield from the metabolism of these sugars; it was calculated that the growth yield data were consistent with the production of 2.8 to 3.2 ATP in the metabolism of glucose 6-phosphate to fermentation products.     

Maintenance energy demand affects biomass synthesis but not cellulase production by a mesophilicClostridium

Summary Secretion of cellulolytic activity by the mesophilClostridium strain C7 was studied while the bacterium underwent progressive carbon/energy starvation and the ensuing continuous decline in growth rate. In the slowest range of growth rates studied the organism was in full response to the global regulation imposed by guanosine 5, 3-bispyrophosphate (ppGpp). The exoenzymes of the cellulase complex were produced at the same volumetric rate whether or not the response was active. However, the volumetric rate of biomass synthesis was reduced 45% or more by the response. Energy necessary to maintain the ppGpp-regulated state (i.e., maintenance energy) was, therefore, diverted from energy going to synthesis of biomass but not from that going to exoenzyme synthesis, making the yield of cellulase activity per mole of carbon-energy substrate independent of growth rate and the exoenzyme complex produced from the substrate with equal efficiency at all growth rates. The primary consideration in improving exoenzyme productivity by bacteria with this type of energy distribution between secretion, growth, and maintenance is simply increasing yield per mole of carbon-energy substrate, with growth rate effects on yield a secondary and minimum concern.     

Data consistency,yield and maintenance coefficient for the growth of Candida lypoytica and Pseudomonas aeruginosa on n-hexadecane

Summary When more than the minimum number of variables are measured, and measurement error is taken into account, the results of parameter estimation depend on which of the measured variables are selected for this purpose. The reparameterization of Pirt's models for growth produces multiresponse models with common parameters. By using the covariate adjustment technique, a unit variate linear model with covariates is obtained. This allows a combined point and interval estimates of biomass energetic yield and maintenance coefficient to be obtained using standard multiple regression programmes. When this method was applied using form I and form II of the Pirt's models, good combined estimates were obtained and compared. Using data from the literature for Candida lipolytica produced reliable results. However, for Pseudomonas aeruginosa, which has been known to produce intermediate products, a modified Pirt's model is required for a good estimate of the biomass energetic yield.Nomenclature a Mole of ammonia per quantity of organic substrate containing 1 g atom carbon, g mole/g atom carbon - b Moles of oxygen per quantity of organic substrate containing 1 g atom carbon, g mole/g atom carbon - c Moles of water per quantity of organic substrate containing 1 g atom carbon, g mole/g atom carbon; no of covariates included in model - d Moles of carbon dioxide per quantity of organic substrate containing 1 g atom carbon, g mole/g atom carbon - e _i Error terms in Eqs. (6–8) - l Atomic ratio of oxygen to carbon in organic substrate, dimensionless - m Atomic ratio of hydrogen to carbon in organic substrate, dimensionless - m _e Rate of organic substrate consumption for maintenance, g equiv. of available electrons in biomass (h) or kcal/Kcal of biomass(h) - n Atomic ratio of oxygen to carbon in biomass, dimensionless - p Atomic ratio of hydrogen to carbon in biomass, dimensionless - Q _{CO 2} Rate of evolution of carbon dioxide, g moles/g dry wt (h) - Q _{O 2} Rate of oxygen consumption, g moles/g dry wt (h) - Q _s Rate of organic substrate consumption g/g dry wt (h) - q Atomic ratio of nitrogen to carbon in biomass, dimensionless - r Atom ratio of hydrogen to carbon in products, dimensionless; the number of parameters of interest - s Atomic ratio of oxygen to carbon in products, dimensionless - t Atomic ratio of nitrogen to carbon in products, dimensionless - r Mean of k responses in Eq. (10) - x _ki Kth response in the ith observation - y _c Biomass carbon yield (fraction of organic substrate carbon in biomass), dimensionless - z _i Covariate matrix - z Fraction of organic substrate carbon in products, dimensionless - a _i Parameters associated with covariates - _s Reductance degree of biomass, equivalents of available electrons per gram atom carbon - Reductance degree of organic substrate, equivalents of available electrons per gram atom carbon - Fraction of energy in organic substrate which is evolved as heat, dimensionless - Fraction of available electrons transferred to biomass; biomass energetic yield - True growth yield - Specific growth rate, h^-1 - _p Fraction of available electrons incorporated into products; product energetic yield - Correlation coefficient - Mass fraction carbon - ² Mean square error of model (10)