Insight into the comprehensive effect of carbon dioxide, light intensity and glucose on heterotrophic-assisted phototrophic microalgae biofilm growth: A multifactorial kinetic model.

Heterotrophic-assisted photoautotrophic microalgae biofilm cultivation was an alternative way to realize CO2 reduction and wastewater treatment. Growth kinetics supplied a channel to better understand how the cultivation conditions affect microalgal growth and CO2 reduction. However, the two growth modes (heterotroph and photoautotroph) have different needs for organic and inorganic nutrients. Thus, combining the threshold theory and multiplication theory, an integral multifactorial kinetic model that looking insight into the comprehensive effect of glucose, CO2, light intensity, and nitrate was developed for heterotrophic-assisted photoautotrophic microalgae biofilm growth in this study. R2 between model and experiment was 0.99. It predicted the maximum specific growth rate and maximum CO2 consumption rate of heterotrophic-assisted photoautotrophic microalgae biofilm was 1.868 h-1 and 1.02 h-1, respectively. This model fully explained the influence of the main factors on microalgae biofilm growth and reasonably predicted the growth rate of microalgae biofilm under different growth conditions.

ANAMMOX-like performances for nitrogen removal from ammonium-sulfate-rich wastewater in an anaerobic sequencing batch reactor.

Ammonium removal by the ANaerobic AMonium OXidation (ANAMMOX) process was observed through the Sulfate-Reducing Ammonium Oxidation (SRAO) process. The same concentration of ammonium (100 mg N L(-1)) was applied to two anaerobic sequencing batch reactors (AnSBRs) that were inoculated with the same activated sludge from the Vermicelli wastewater treatment process, while nitrite was fed in ANAMMOX and sulfate in SRAO reactors. In SRAO-AnSBR, in substrates that were fed with a ratio of NH4(+)/SO4(2-) at 1:0.4 ± 0.03, a hydraulic retention time (HRT) of 48 h and without sludge draining, the Ammonium Removal Rate (ARR) was 0.02 ± 0.01 kg N m(-3).d(-1). Adding specific ANAMMOX substrates to SRAO-AnSBR sludge in batch tests results in specific ammonium and nitrite removal rates of 0.198 and 0.139 g N g(-1) VSS.d, respectively, indicating that the ANAMMOX activity contributes to the removal of ammonium in the SRAO process using the nitrite that is produced from SRAO. Nevertheless, the inability of ANAMMOX to utilize sulfate to oxidize ammonium was also investigated in batch tests by augmenting enriched ANAMMOX culture in SRAO-AnSBR sludge and without nitrite supply. The time course of sulfate in a 24-hour cycle of SRAO-AnSBR showed an increase in sulfate after 6 h. For enriched SRAO culture, the uptake molar ratio of NH4(+)/SO4(2-) at 8 hours in a batch test was 1:0.82 lower than the value of 1:0.20 ± 0.09 as obtained in an SRAO-AnSBR effluent, while the stoichiometric ratio of 1:0.5 that includes the ANAMMOX reaction was in this range. After a longer operation of more than 2 years without sludge draining, the accumulation of sulfate and the reduction of ammonium removal were observed, probably due to the gradual increase in the sulfur denitrification rate and the competitive use of nitrite with ANAMMOX. The 16S rRNA gene PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) and PCR cloning analyses resulted in the detection of the ANAMMOX bacterium (Candidatus Brocadia sinica JPN1) Desulfacinum subterraneum belonging to the genus Desulfacinum and bacteria that are involved in sulfur metabolism (Pseudomonas aeruginosa strain SBTPe-001 and Paracoccus denitrificans strain IAM12479) in SRAO-AnSBR.

High current densities enable exoelectrogens to outcompete aerobic heterotrophs for substrate.

In mixed-culture microbial fuel cells (MFCs), exoelectrogens and other microorganisms compete for substrate. It has previously been assumed that substrate losses to other terminal electron acceptors over a fed-batch cycle, such as dissolved oxygen, are constant. However, a constant rate of substrate loss would only explain small increases in coulombic efficiencies (CEs, the fraction of substrate recovered as electrical current) with shorter cycle times, but not the large increases in CE that are usually observed with higher current densities and reduced cycle times. To better understand changes in CEs, COD concentrations were measured over time in fed-batch, single-chamber, air-cathode MFCs at different current densities (external resistances). COD degradation rates were all found to be first-order with respect to COD concentration, even under open circuit conditions with no current generation (first-order rate constant of 0.14 ± 0.01 h(-1) ). The rate of COD removal increased when there was current generation, with the highest rate constant (0.33 ± 0.02 h(-1) ) obtained at the lowest external resistance (100 Ω). Therefore, as the substrate concentration was reduced more quickly due to current generation, the rate of loss of substrate to non-exoelectrogens decreased due to this first-order substrate-concentration dependence. As a result, coulombic efficiencies rapidly increased due to decreased, and not constant, removal rates of substrate by non-exoelectrogens. These results show that higher current densities (lower resistances) redirect a greater percentage of substrate into current generation, enabling large increase in CEs with increased current densities. Biotechnol. Bioeng. 2014;111: 2163-2169. © 2014 Wiley Periodicals, Inc.

Macroscopic modeling of the growth and substrate consumption of wild type and genetically modified Pichia pastoris.

Pichia pastoris is a popular yeast platform to generate several industrially relevant products which have applications in a wide range of sectors. The complexities in the processes due to the addition of a foreign gene are not widely explored. Since these complexities can be dependent on the strain characteristics, promoter, and type of protein produced, it is vital to investigate the growth and substrate consumption patterns of the host to facilitate customized process optimization. In this study, the growth rates of P. pastoris GS115 wild type (WT) and genetically modified (GM) strains grown on glycerol and methanol in batch cultivation mode were estimated and the model providing the best representation of the true growth kinetics based on substrate consumption was identified. It was observed that the growth of P. pastoris exhibits Haldane kinetics on glycerol rather than the most commonly used Monod kinetics due to the inability of the latter to describe growth inhibition at high concentrations of glycerol. Whereas, the cardinal parameter model, a newly proposed model for this application, was found to be the best fitting to describe the growth of P. pastoris on methanol due to its ability to describe methanol toxicity. Interestingly, the findings from this study concluded that in both substrates, the genetically engineered strain exhibited a higher growth rate compared to the WT strain. Such an observation has not been established yet in other published works, indicating an opportunity to further optimize the carbon source feeding strategies when the host is grown in fed-batch mode.

The effects of dynamic bacterial succession on the flavor metabolites during Baijiu fermentation.

The succession of microbial community significantly affect the flavor formation of traditional fermented foods and beverages. Chinese liquor (Baijiu) fermentation is a typical spontaneous solid-state fermentation process driven by natural microbiota. The type of process used to make liquor-craft or industrial-alters the operational environment and the aromatic qualities of the product contributed by various microbial consortia. But differences in microbial community assembly and temporal succession are often overlooked. In this study, we investigated bacterial community dynamics, substrate consumption, and metabolite production during both craft and industrial liquor-making processes (CLP and ILP, respectively). We found that the compositions of bacterial communities were different, even though no significant difference (p > 0.05) was observed in bacterial species between CLP and ILP at the beginning of fermentation. During ILP, glucose was used more rapidly by microflora, leading in turn to a higher ethanol production rate during the early stage of fermentation. The higher rate of ethanol production in ILP shortened the lifetime of bacteria such as Weissella, Pediococcus, Leuconostoc, and Bacillus during the early stage of fermentation. Lactobacillus sp. became dominant earlier in ILP than in CLP. Finally, the change in bacterial community dynamics led to changes in aroma compounds. Using CLP and ILP as a model system, our results illustrate the dynamic nature of Baijiu fermentations and microbial succession patterns therein. This can be applied to optimize the fermentation processes and flavors attributes of this and other fermented foods.

Physiological Response of Corynebacterium glutamicum to Increasingly Nutrient-Rich Growth Conditions.

To ensure economic competitiveness, bioprocesses should achieve maximum productivities enabled by high growth rates (µ) and equally high substrate consumption rates (qS) as a prerequisite of sufficient carbon-to-product conversion. Both traits were investigated and improved via bioprocess engineering approaches studying the industrial work horse Corynebacterium glutamicum. Standard minimal medium CGXII with glucose as sole carbon source was supplemented with complex brain-heart-infusion (BHI) or amino acid (AA) cocktails. Maximum µ of 0.67 h-1 was exclusively observed in 37 g BHI L-1 whereas only minor growth stimulation was found after AA supplementation (µ = 0.468 h-1). Increasing glucose consumption rates (qGlc) were solely observed in certain dosages of BHI (1-10 g L-1), while 37 g BHI L-1 and AA addition revealed qGlc below the reference experiments. Moreover, BHI supplementation revealed Monod-type saturation kinetics of µ (KBHI = 2.73 g BHI L-1) referring to the preference of non-AAs as key boosting nutrients. ATP-demands under reference, 1 g BHI L-1, and AA conditions were nearly constant but halved in BHI concentrations above 5 g L-1 reflecting the energetic advantage of consuming complex nutrient components in addition to "simple" building blocks such as AAs. Furthermore, C. glutamicum revealed maximum biomass per carbon yields of about 18 gCDW C-mol-1 irrespective of the medium. In AA supplementation experiments, simultaneous uptake of 17 AAs was observed, maximum individual consumption rates determined, and L-asparagine and L-glutamine were distinguished as compounds with the highest consumption rates. Employment of the expanded stoichiometric model iMG481 successfully reproduced experimental results and revealed the importance of C. glutamicum's transaminase network to compensate needs of limiting AA supply. Model-based sensitivity studies attributed the highest impact on µ to AAs with high ATP and NADPH demands such as L-tryptophan or L-phenylalanine.

Biosynthesis of poly(hydroxybutyrate-hydroxyvalerate) from the acclimated activated sludge and microbial characterization in this process.

This study investigated the effects of substrate composition (acetate and propionate) on synthesis of various mix of poly(hydroxybutyrate-hydroxyvalerate) (P(HB/HV)) from activated sludge, which was acclimated using a single carbon (acetate) and mixed carbons (acetate and propionate). Results of batch P(HB/HV) production tests indicated that the yield and synthesis rate of P(HB/HV) decreased as the proportion of propionate in the substrate increased. However, mixed-carbon-acclimated sludge with acetate and propionate exhibited better P(HB/HV) production performance than with acetate-acclimated sludge in terms of substrate utilization, yield of P(HB/HV) and HV fraction in P(HB/HV). The desired hydroxyvalerate (HV) fraction (0-74%) of the P(HB/HV) could be obtained based on the substrate composition and sludge acclimation. Furthermore, PCR-DGGE analysis indicated that specific species dominated the activated sludge used for P(HB/HV) production. Acidobacteria and Burkholderiales were the dominant bacterial populations and played an important role in HV synthesis.

Utilization of a waste glycerol fraction using and reusing immobilized Gluconobacter oxydans ATCC 621 cell extract

Background: Depletion of petroleum resources has enforced the search for alternative sources of renewable energy. Introduction of biofuels into the market was expected to become a solution to this disadvantageous situation. Attempts to cover fuel demand have, however, caused another severe problem­the waste glycerol generated during biodiesel production at a concentration of approximately 10% w/w. This, in turn, prompted a global search for effective methods of valorization of the waste fraction of glycerol. Results: Utilization of the waste fraction at 48 h with an initial glycerol concentration of 30 g·L-1 and proceeding with 62% efficiency enabled the production of 9 g·L-1 dihydroxyacetone at 50% substrate consumption. The re-use of the immobilized biocatalyst resulted in a similar concentration of dihydroxyacetone (8.7 g·L-1) in two-fold shorter time, with an efficiency of 85% and lower substrate consumption (35%). Conclusions: The method proposed in this work is based on the conversion of waste glycerol to dihydroxyacetone in a reaction catalyzed by immobilized Gluconobacter oxydans cell extract with glycerol dehydrogenase activity, and it could be an effective way to convert waste glycerol into a valuable product.

Efecto de la melaza de caña tratada con ácido sulfúrico en la producción de celulosa por Gluconacetobacter xylinus IFO 13693 / Effect of molasses cane treated with sulfuric acid in the production of cellulose by Gluconacetobacter xylinus IFO 13693 / Efeito do melaço de cana tratada com ácido sulfúrico na produção de celulose por Gluconacetobacter xylinus IFO 13693

En este estudio se evaluó el efecto de la melaza tratada con ácido sulfúrico (MZA-TR) y de las condiciones del cultivo (estático) sobre la síntesis de celulosa por Gluconacetobacter xylinus IFO 13693, para ello, se usó un reactor con 0,2 litros de medio de cultivo, con concentraciones iniciales de 13,3 % y 26,6 % de MZA-TR en el medio de cultivo a pH 5,6. El volumen del inóculo fue del 10 % del volumen total del medio; el proceso se realizó a temperatura ambiente (30 °C), con tiempos de incubación de 3, 7, 14, 21 y 28 días. Además, se evaluaron distintos parámetros fisicoquímicos y mecánicos de la celulosa. El grosor de la película de celulosa presentó un máximo de 2,5 cm, siendo el mejor resultado obtenido, en comparación con anteriores reportes en la literatura. También se encontró que al usar MZA-TR en el medio de cultivo hay un incremento considerable de la producción de celulosa en estático a los 28 días de incubación. Finalmente, se observó que el consumo de glucosa y de fructosa disminuye durante la síntesis de celulosa bacteriana (CB); durante los 3 primeros días de incubación se observó el máximo descenso, lo que permite correlacionar la producción de CB con el consumo de medio. La concentración de 13,3 %, presenta los mejores resultados en los parámetros de velocidad de crecimiento microbiano, cantidad y calidad de la celulosa producida.

This study assessed the effect of molasses treated with sulfuric acid (MZA-TR) and the condition of the crop (static) on the synthesis of cellulose by Gluconacetobacter xylinus IFO 13693, using a reactor with 0,2 liters of growing medium, with initial concentrations of 13,3 % and 26,6 % of molasses treated (MZA-TR) in the culture medium at pH 5,6. The volume of the inoculum was 10 per cent of the total volume of the environment; the process was carried out at ambient temperature (30 °C), with times of incubation of 3, 7, 14, 21 and 28 days. Also, different physico-chemical and mechanical parameters of the pulp were evaluated. The thickness of the cellulose film presented a maximum of 2.5 cm, being the best result obtained, in comparison to previous reports in the literature. Furthermore, it was found that using MZA-TR in the middle considerably increased the production of cellulose in static at 28 days of incubation. Finally, it was observed that the consumption of glucose and fructose decreased during the synthesis of Bacterial Cellulose (BC); during the first 3 days of incubation it was noted the maximum decline, which allows to correlate the production of CB with the consumption of media. The concentration of 13.3 %, presents the best results in the speed parameters of microbial growth, the quantity and quality of cellulose produced.

Neste estudo foi avaliado o efeito do melaço tratado com ácido sulfúrico (MZA-TR) e das condições da cultura (estática) sobre a síntese de celulose pelo Gluconacetobacter xylinus IFO 13693. Para isso, foi utilizado um reator com 0,2 litros de meio de cultura, com concentrações iniciais de 13,3 e 26,6% de MZA-TR, e pH igual a 5,6. O volume de inoculo foi de 10% do volume total do meio, e o processo foi realizado a temperatura ambiente (30°C), com tempos de 3, 7, 14, 21 e 28 dias. Além disso, foram avaliados os distintos parâmetros físico-químicos e mecânicos da celulose. A espessura máxima que apresentou o filme de celulose foi de 2,5 cm, sendo o melhor resultado obtido, ao comparar com os reportados anteriormente na literatura. Verificou-se também que ao usar MZA-TR no meio de cultura houve um aumento considerável na produção de celulose no meio estático aos 28 dias de incubação. Finalmente foi observado que o consumo de glicose e frutose diminuiu durante a síntese de celulose bacteriana (CB). Durante os três primeiros dias de incubação verificou-se a diminuição máxima, o que permite correlacionar a produção de CB com o consumo do meio. A concentração de 13,3% apresentou os melhores resultados nos parâmetros da velocidade de crescimento microbiano, quantidade e qualidade da celulose produzida.