Higher Oxygen Uptake Rate Research Articles

Rapid physiological and transcriptomic changes associated with oxygen delivery in larval anemonefish suggest a role in adaptation to life on hypoxic coral reefs.

Connectivity of coral reef fish populations relies on successful dispersal of a pelagic larval phase. Pelagic larvae must exhibit high swimming abilities to overcome ocean and reef currents, but once settling onto the reef, larvae transition to endure habitats that become hypoxic at night. Therefore, coral reef fish larvae must rapidly and dramatically shift their physiology over a short period of time. Taking an integrative, physiological approach, using swimming respirometry, and examining hypoxia tolerance and transcriptomics, we show that larvae of cinnamon anemonefish (Amphiprion melanopus) rapidly transition between "physiological extremes" at the end of their larval phase. Daily measurements of swimming larval anemonefish over their entire early development show that they initially have very high mass-specific oxygen uptake rates. However, oxygen uptake rates decrease midway through the larval phase. This occurs in conjunction with a switch in haemoglobin gene expression and increased expression of myoglobin, cytoglobin, and neuroglobin, which may all contribute to the observed increase in hypoxia tolerance. Our findings indicate that critical ontogenetic changes in the gene expression of oxygen-binding proteins may underpin the physiological mechanisms needed for successful larval recruitment to reefs.

Abyssal fauna, benthic microbes, and organic matter quality across a range of trophic conditions in the western Pacific ocean

The abyssal plain covers more than half the Earth’s surface. The main food source to abyssal ecosystems is phytodetritus, which originates from phytoplankton in the surface ocean, and thus its variability to the seafloor is a major driver of abyssal ecosystem biomass and functioning. In this study, we conducted a comparative survey on organic matter (OM) quality and quantity in abyssal plain sediments and examined the distributions of megafauna, macrofauna, meiofauna, prokaryotes, and viruses in eutrophic (39°N), oligotrophic (1°N), and ultra-oligotrophic (12°N) areas of the western Pacific. We also analyzed stable carbon and nitrogen isotopic compositions of organisms at 39°N and 1°N to assess differences in benthic abyssal food-web structures with contrasting trophic states. Sediments collected at 39°N presented highest concentrations of total organic carbon (TOC) and labile OM, and high diffusive oxygen uptake rates. By contrast, the lowest values were found at 12°N. Vertical distributions of sediment macrofauna, meiofauna, and prokaryotes matched with labile OM profiles. There were prominent differences in abundances of macro- and megafauna among stations with different OM fluxes, whereas the abundance of meiofauna and prokaryotes showed smaller differences among stations. Such differences could be explained by higher turnover rates of smaller organisms. Food-web structures of abyssal plains are likely influenced by both the type and size of primary producers in surface ocean. Our results underscore the crucial importance of OM fluxes and their compositions to the abundances and vertical profiles of labile OM and benthic biota in abyssal ecosystems.

Integrated selection and identification of bacteria from polluted sites for biodegradation of lipids.

Wastewater treatment plants face major social concern towards removal of problematic pollutants such as fat oils and grease (FOG). In this context, the main objective of the present work was to select natural bacterial isolates from different polluted sites and evaluate them comparatively to isolates from commercial products, for improved bioremediation strategies and bioaugmentation. In total, 196 isolates were analysed for genomic diversity by two PCR-fingerprinting methods and screened for biodegradation potential with pollutants as sole carbon source. The net area under curve (NAUC) was used for preliminary evaluation of growth ability in M9 medium supplemented with oleic acid and triolein. A principal component analysis of all NAUC data showed that natural isolates presented higher overall biodegradation ability and enabled the selection of 11 natural isolates for lipid degradation assays. Selected isolates were identified by 16S rRNA gene sequencing as members of genera with previously described degradative strains, namely, Acinetobacter (1), Aeromonas (2), Bacillus (1), Pseudomonas (1) and Staphylococcus (6). Best biodegradation results in 7-days assay of FOG content removal were 37.9% for oleic acid and 19.1% for triolein by an Aeromonas sp. isolate and a Staphylococcus cohnii isolate, respectively. A respirometry approach confirmed their higher oxygen uptake rates, although longer adaptation phases where required by the Aeromonas sp. isolate. Consequently, these isolates showed great potential for future bioaugmentation products, to promote FOG degradation, for both in situ and ex situ approaches.

Quantitative Oxygen Consumption and Respiratory Activity of Meat Spoiling Bacteria Upon High Oxygen Modified Atmosphere.

High oxygen modified atmosphere packaging is a commonly applied method to prolong the minimum shelf life of fresh (red) meats. Upon spoilage, changes of the initial oxygen concentration and microbiome composition can be observed. Thus, we classified the typical representative meat spoiling bacteria Brochothrix (B.) thermosphacta TMW2.2101 and the four lactic acid bacteria (LAB) Carnobacterium (C.) divergens TMW2.1577, C. maltaromaticum TMW2.1581, Leuconostoc (L.) gelidum subsp. gelidum TMW2.1618, and L. gelidum subsp. gasicomitatum TMW2.1619 along their oxygen consuming capacity, which can indicate the timeline of microbiome and sensorial changes. All bacteria were grown in a model system employing gas tight glass bottles containing meat simulation media and under modified atmosphere (70% O2 and 30% CO2). Oxygen concentrations of media and headspaces were monitored over time and the oxygen uptake rate (OUR) was calculated for all species. All bacteria were able to consume dissolved oxygen, with B. thermosphacta TMW2.2101 exhibiting a 31-times higher OUR per single cell in 60 h. Furthermore, all strains showed significant growth enhancement in the presence of heme indicating respiratory activity. Comparative genomic and physiological analyses predict the activity of a respiratory chain for all species upon high oxygen atmosphere. An additional cytochrome aa3 oxidase is suggested to be responsible for the increased OUR of B. thermosphacta TMW2.2101. Furthermore, B. thermosphacta TMW2.2101 revealed highest oxidative stress tolerance compared to the other bacteria, facilitating a higher respiratory activity. Coupling of respiration and fermentation via regeneration of NADH can be a competitive advantage for meat spoiling bacteria resulting in a higher cell count and possibly accelerated spoilage. The exhibited highest capacity for oxygen consumption of B. thermosphacta compared to LAB in vitro also suggests a higher contribution of this bacterium to the change in the atmosphere upon spoilage of MAP meats in situ.

Diethylhexyl phthalate removal in full scale activated sludge plants: Effect of operational parameters

Removal of emerging contaminants (ECs) is a serious concern in wastewater industry especially for public acceptance of reclaimed water. Diethylhexyl phthalate (DEHP) is one of the ubiquitous and detectable plasticizers in municipal wastewater across the globe. Water Framework Directive (2000/60/EC) has prioritized it for the establishment of discharge regulations. A cost-effective strategy, especially for developing nations, may be the re-engineering of the existing biological process for the simultaneous removal of ECs and conventional pollutants. Wastewater treatment plants are one of the main sources for DEHP occurrence in surface water. In this study, possible role of activated sludge process operational parameters in effective removal of DEHP was assessed. Principal component analysis of occurrence data showed dissimilarity with the organic and nutrient characteristics of sewage. DEHP concentration in more than half (55%) of treated wastewater samples was more than environmental quality standard value for inland and surface water bodies (1.3 μg/L). At a mixed liquor suspended solid (MLSS) concentration range of 3461–4972 mg/L, overall removal was 23.9 μg/gMLSS.d (92 ± 6%) with biodegraded portion as 22.4 μg/gMLSS.d (85 ± 4%) and sorbed portion of 1.5 μg/gMLSS.d (7 ± 4%). DEHP removal showed an increasing trend at higher oxygen uptake rates (OUR) of sludge with DEHP removal of 8.1 μg DEHP/gMLSS.d (70 ± 6%), in the OUR range of 20-28mgO2/L/h. Increase in overall removal of DEHP showed a positive correlation (r2 = 0.7) with increasing sludge retention time (SRT) and so does the decreasing food to microorganism (F/M) ratio with increasing removal of DEHP (r2 = 0.8). A temperature decrease of 13 °C caused a decrease of 30% in overall removal of DEHP.

Energetic enhancement of thermal assistance in the cooling stage of biodrying by stimulating microbial degradation

In this study, thermal assistance was employed in the cooling stage of conventional biodrying. The results indicated that thermal assistance greatly enhanced water removal with improved vapor-carrying capacity of air-flow, and rapidly decreased moisture contents (MCs) from 45.15% to 49.42% to 15.20–25.85% in 6 days, which were much lower than those of conventional biodrying (CB, 34.90–40.85%). More importantly, a synergistic enhancement of physical and biological effects was observed in thermally assisted biodrying (TB) in terms of stimulated enzymes activity and microbial metabolism (higher oxygen uptake rate and degradation coefficient k). Among the degraded organics, lignocellulose was noted to be important for bio-heat generation in cooling stages, especially for straw as bulking agent. Heat balance results suggested that small fractions of thermal heat (19.76–24.73%) were required to upgrade CB processes for water evaporation with higher energy efficiency. Based on economic viability analysis and with consideration of the further drying for CB products, thermally assisted biodrying presented more economic benefits with less investment and shorter payback period. This research provided an efficient engineering approach to upgrade the cooling stage of conventional biodrying with low external heat cost.

Comprehensive study on Wave bioreactor system to scale up the cultivation of and recombinant protein expression in baculovirus-infected insect cells

Although the baculovirus expression vector system has been widely used to produce a variety of recombinant proteins, the shear sensitivity of insect cells besides their relatively high oxygen uptake rates have limited their large scale applicability. To address such issues, Wave bioreactor systems have been developed to provide the insect cells with sufficient dissolved oxygen in a bubble free medium of minimal shear stress. However, selection of rocking parameters, and the methods used to control the processes have not been well described in literature. Herein, oxygen transfer capacity of Wave bioreactor has been investigated at different combinations of rocking parameters. Considering the specific oxygen uptake rates (SOUR) and the assessed oxygen transfer capacity of the Wave bioreactor, rocking parameters were set to cultivate non-infected Spodoptera frugiperda 9 cells and infected/non-infected BTI-TN-5B1-4 cells in 2 L Cellbags. The obtained results were exploited to estimate the SOUR of the insect cells under actual condition of Wave bioreactor system. Furthermore, although Express Five medium was recommended by the supplier, the yield of the active soluble human papillomavirus (HPV) 16L1 protein expression was improved in Sf900 II medium. Using the obtained results, protein expression in BTI-TN-5B1-4 cells was finally scaled up to 50 L confirming that the obtained information could be successfully used to scale the Wave bioreactor by specifying the rocking parameters.

Oxygen Transfer at the Sediment/Water Interface for Sediment Bed With Rough Surface

AbstractA model of sediment oxygen demand (SOD) for a sediment bed with a rough surface was presented. The equivalent sand roughness commonly used in hydraulics was chosen to express the size of roughness elements, and SOD was expressed as a function of the intensity of near‐bed turbulence described by the shear velocity; microbial oxygen uptake rate, that is, the maximum oxidation rate; and roughness height. The modeling results show that bed roughness enhances oxygen transfer from the water column to the sediment surface. The effects of bed roughness on SOD depend on both the shear velocity and microbial oxygen uptake rate. At low microbial oxygen uptake rate, SOD approaches a constant value rapidly as the shear velocity increases. Bed roughness barely influences SOD regardless of the shear velocity because SOD can substantially be sediment side limiting. The roughness height plays an important role in determining SOD at high microbial oxygen uptake rate, because SOD can be controlled by oxygen transfer from the water column to the sediment surface, that is, transfer limiting. Increasing roughness height makes the oxygen transfer rate from flowing water to the sediment surface faster as well as increasing shear velocity, resulting in raised SOD. The proposed mode can substantially reproduce the experimental SOD for rough bed.

Influence of recovery duration during 6-s sprint interval exercise on time spent at high rates of oxygen uptake

Background/ObjectiveThis study examined whether time spent at high rates of oxygen consumption (VO2) during 6-s sprint interval exercises (SIE) is a function of recovery interval duration. MethodsIn a randomised crossover study, thirteen male endurance runners performed 40 × 6-s all-out sprints interspersed with 15-s, 30-s and 60-s passive recovery intervals (SIE15, SIE30, and SIE60 trials respectively), and a work duration-matched Wingate-SIE (8 × 30-s all-out sprints with 4-min passive recovery, SIEWin trial). The accumulated exercise time at ≥ 80%, 85%, 90%, 95% and 100% of VO2max, and maximum heart rate (HRmax) in the four trials were compared. ResultsDuring the 6-s SIEs, accumulated time spent at all selected high rates of VO2max increased as recovery time decreased, whilst the SIE work rate decreased (p < .05). In SIEWin, although the exercise lasted longer, the time spent at ≥90% VO2max (74 ± 16 s) was significant less than that in SIE15 (368 ± 63 s, p < .05), yet comparable to that in SIE30 (118 ± 30 s, p > .05), and longer than that in SIE60 (20 ± 14 s, p < .05). The differences between the four trials in accumulated time at high percentages of HRmax were similar to those for VO2, although the temporal characteristics of the increases in HR and VO2 during the SIEs were different. ConclusionIn conclusion, the duration of the recovery interval in 6-s SIE protocols appears to be a crucial parameter when sprint interval training is prescribed to enhance aerobic capacity. Further, the SIE15 protocol may represent a potential alternative to 30-s SIEWin in the development of time-efficient aerobic training intervention.

Membrane fouling control and enhanced removal of pharmaceuticals and personal care products by coagulation-MBR

We investigated the effects of the addition of two coagulants−polyaluminium chloride (PACl) and chitosan−into the membrane bioreactor (MBR) process on membrane fouling and the removal of pharmaceuticals and personal care products (PPCPs). Their addition at optimized dosages improved the permeability of the membrane by reducing the concentration of soluble microbial products in mixed liquor, the content of inorganic elements, and irreversible fouling of the membrane surface. During long-term operation, the addition of PACl increased removal efficiencies of tetracycline, mefenamic acid, atenolol, furosemide, ketoprofen, and diclofenac by 17–23%. The comparative evaluation using mass balance calculations between coagulation-MBR (with PACl addition) and control-MBR (without PACl addition) showed that enhanced biodegradability played a key role in improving removal efficiencies of some PPCPs in coagulation-MBR. Coagulation-MBR also had higher oxygen uptake rates and specific nitrification rates of microorganisms. Overall, our findings suggest that the combination of MBR with coagulation reduced membrane fouling, lengthening operation period of the membrane, and improved the removal of some PPCPs as a result of enhanced biodegradability.

Metabolite profiling coupled with metabolic flux analysis reveals physiological and metabolic impacts on Lactobacillus paracasei oxygen metabolism

Abstract In this study, the impacts of oxygen metabolism characterized by oxygen uptake rate (OUR) on lactic acid production in Lactobacillus paracasei were investigated through metabolite profiling and metabolic flux analysis. At growth phase, with the cost of declining lactic acid yield, the cells shifted pyruvate metabolism from lactic acid production to ATP high-yielding acetate synthesis to guarantee sufficient energy supply for cell growth under high OUR condition. When the cells reached to stationary phase, significant glucose metabolism inhibition happened with high OUR level due to much more reactive oxygen species (ROS) accumulation in the cells, which subsequently would attack glycolytic key enzyme, glycerate-3-phosphate dehydrogenase (GAPDH), leading to the substantial limitation of glucose consumption. Moreover, other than glucose metabolism restriction, the decline on metabolic level regulation of lactic acid yield further decreased lactic acid productivity. On the other hand, it was interestingly found that intracellular redox balance was greatly dependent on acetyl-CoA node (acetate/ethanol) in growth phase, and acetoin node (acetoin/2,3-butanediol) in stationary phase respectively. The application of integrated metabolite profiling and metabolic flux analysis highlighted the regulation of energy and redox metabolism in lactic acid production by L. paracasei.

Effect of PVA-gel filling ratio in attached growth membrane bioreactor for treating polluted surface water

ABSTRACTSurface water has been facing increasing loads of various types of organic contamination due to human activities. Attached growth membrane bioreactor (aMBR) has been reported as a promising approach in treating polluted surface water. By using bio-carrier to provide biodegradation and utilize organic pollutants as substrates, aMBR was able to integrate biodegradation and physical rejection in one system. The filling ratio of polyvinyl alcohol gel (PVA-gel), which is an important bioprocess contributor in an aMBR system, was analyzed by batch test and lab-scale aMBR in this study. Batch test with various filling ratios (2%, 5%, 10%, 15% and 30%) were carried out. Oxygen uptake rate (OUR) and specific oxygen uptake rate were used for the comparison of bioactivities. Five percent filling ratio had the highest OUR results of 3.6 mg/L h obtained from the batch test. The chosen filling ratios were tested in a lab-scale aMBR system with hydraulic retention time (HRT) of 1, 2, 2.5 and 3 h. Results shown that at HRT 2.5 h, the aMBR system had the lowest membrane fouling. PVA-gel was able to reject more organic matters than a naturally immobilized membrane bioreactor system, and thus mitigated membrane fouling in the aMBR system.

Enhancement of l-phenylalanine production in Escherichia coli by heterologous expression of Vitreoscilla hemoglobin.

l-Phenylalanine is an important amino acid that is widely used in the production of food flavors and pharmaceuticals. Generally, l-phenylalanine production by engineered Escherichia coli requires a high rate of oxygen supply. However, the coexpression of Vitreoscilla hemoglobin gene (vgb), driven bya tac promoter, with the genes encoding 3-deoxy-d-arabinoheptulosonate-7-phosphate synthetase (aroF) and feedback-resistant chorismate mutase/prephenate dehydratase (pheAfbr ), led to increased productivity and decreased demand for aeration by E. coli CICC10245. Shake-flask studies showed that vgb-expressing strains displayed higher rates of oxygen uptake, and l-phenylalanine production under standard aeration conditions was increased. In the aerobicfermentation process, cell growth, l-phenylalanine production, and glucose consumption by the recombinant E. coli strain PAPV, which harbored aroF, pheAfbr , and tac-vgb genes, were increased compared to that in the strain harboring only aroF and pheAfbr (E. coli strain PAP), especially under oxygen-limited conditions. The vgb-expressing strain PAPV produced 21.9% more biomass and 16.6% more l-phenylalanine, while consuming only approximately 5% more glucose after 48 H of fermentation. This study demonstrates a method to enhance the l-phenylalanine production by E. coli using less intensive and thus more economical aeration conditions.

Oxygen dynamics in shelf seas sediments incorporating seasonal variability

Shelf sediments play a vital role in global biogeochemical cycling and are particularly important areas of oxygen consumption and carbon mineralisation. Total benthic oxygen uptake, the sum of diffusive and faunal mediated uptake, is a robust proxy to quantify carbon mineralisation. However, oxygen uptake rates are dynamic, due to the diagenetic processes within the sediment, and can be spatially and temporally variable. Four benthic sites in the Celtic Sea, encompassing gradients of cohesive to permeable sediments, were sampled over four cruises to capture seasonal and spatial changes in oxygen dynamics. Total oxygen uptake (TOU) rates were measured through a suite of incubation experiments and oxygen microelectrode profiles were taken across all four benthic sites to provide the oxygen penetration depth and diffusive oxygen uptake (DOU) rates. The difference between TOU and DOU allowed for quantification of the fauna mediated oxygen uptake and diffusive uptake. High resolution measurements showed clear seasonal and spatial trends, with higher oxygen uptake rates measured in cohesive sediments compared to the permeable sediment. The significant differences in oxygen dynamics between the sediment types were consistent between seasons, with increasing oxygen consumption during and after the phytoplankton bloom. Carbon mineralisation in shelf sediments is strongly influenced by sediment type and seasonality.

Optimization of Herbicidin A Production in Submerged Culture of Streptomyces scopuliridis M40.

Herbicidin A is a potent herbicide against dicotyledonous plants as well as an antibiotic against phytopathogens. In this study, fermentation parameters for herbicidin A production in submerged culture of Streptomyces scopuliridis M40 were investigated. The herbicidin A concentration varied with the C/N ratio. High C/N ratios (>4) resulted in a herbicidin A production of more than 900 mg/l, whereas maximally 600 mg/l was obtained at ratios between 1 and 3.5. In 5-L batch fermentation, there was a positive correlation between the oxygen uptake rate (OUR) and herbicidin A production. Once the OUR increased, the substrate consumption rate increased, leading to an increase in volumetric productivity. Mechanical shear force affected the hyphal morphology and OUR. When the medium value of hyphal size ranged from 150 to 180 μm, high volumetric production of herbicidin A was obtained with OUR values >137 mg O2/l·h. The highest herbicidin A concentration of 956.6 mg/l was obtained at 500 rpm, and coincided with the highest relative abundance of hyphae of 100-200 μm length and the highest OUR during cultivation. Based on a constant impeller tip speed, which affects hyphal morphology, herbicidin A production was successfully scaled up from a 5-L jar to a 500-L pilot vessel.

Sedimentary oxygen dynamics in a seasonally hypoxic basin

AbstractSeasonal hypoxia refers to the oxygen depletion that occurs in summer in the bottom water of stratified systems, and is increasingly observed in coastal areas worldwide. The process induces a seasonal cycle on the biogeochemistry of the underlying sediments, which remains poorly quantified. Here, we investigated the sedimentary oxygen consumption within Lake Grevelingen (The Netherlands), a saline coastal reservoir that is impacted by yearly recurrent bottom water hypoxia. Monthly sampling campaigns were conducted throughout 2012 at three sites along a depth gradient. Macrofauna sampling and sediment profile imaging demonstrated how summer hypoxia strongly impacts the benthic communities below 15 m of water depth. Benthic fluxes of oxygen, dissolved inorganic carbon, total alkalinity, and ammonium were determined by closed core incubations, while oxygen depth profiles were recorded by microsensor profiling of sediment cores. Our results reveal a pronounced seasonality in the sedimentary oxygen consumption. Low uptake rates in summer were caused by oxygen limitation, and resulted in the build‐up of an “oxygen debt” through the accumulation of reduced iron sulfides. Highest oxygen uptake rates were recorded in fall, linked to the reoxidation of the pool of iron sulfides in the top layer. However, uptake rates remained unexpectedly high during winter and early spring, likely associated with the oxidation of iron sulfides down to centimeters depth due to the electrogenic sulfur oxidation by cable bacteria. Overall, our results suggest that the sedimentary oxygen dynamic in seasonally hypoxic coastal systems is characterized by a strongly amplified “oxygen debt” dynamics induced by cable bacteria.

Application of plow-tillage as an innovative technique for eliminating overwintering cyanobacteria in eutrophic lake sediments

Surface sediment in eutrophic lakes is both a destination and a habitat for overwintering cyanobacteria. The resuspension and recovery of viable, overwintering cyanobacteria from the surface sediment during warm spring weather is usually the primary stage of cyanobacterial blooms (CBs) in shallow eutrophic lakes. Therefore, the elimination of overwintering cyanobacteria in sediment is vital to control CBs. In the present study, sediment plow-tillage (PT) was introduced as an innovative technique for eliminating overwintering cyanobacteria in sediments from Lake Chaohu. Four depths of PT (2, 5, 10, and 15 cm) were tested during the 42-day experiment. The results showed that rapid cell death during the first 0–7 d after PT was accompanied by high oxygen uptake rates. The viable cells in deeper sediment died more quickly and at a higher rate after PT. A PT depth of >10 cm effectively eliminated viable cyanobacteria (with a removal rate of 82.8%) from the sediment and prevented their resuspension. The activity of the viable cyanobacteria also decreased quickly as cyanobacteria were eliminated. It appears that the dark, anoxic environment of the deeper sediment after PT was responsible for the elimination of viable cells. Although high release rates of nitrogen and phosphorus were found to accompany the dying and decomposition of cyanobacteria during days 0–7 of the experiment, greater depth of PT was found to decrease nutrient concentrations in the overlying water. In conclusion, we recommend sediment PT as a new technique for eliminating overwintering algae in sediments. However, the release of nutrients from the sediment and the in situ control of CBs in lakes after PT should be further studied.

Development of a real-time bioprocess monitoring method for docosahexaenoic acid production by Schizochytrium sp.

Oxygen uptake rate (OUR) and respiratory quotient (RQ) are key respiratory parameters for docosahexaenoic acid (DHA) production by Schizochytrium sp. HX-308 under dissolved oxygen limited conditions. To investigate the relationship of OUR and RQ with culture status, three independent cultures with different aeration rates were performed in a 50L bioreactor. OUR was found to be positively correlated with the aeration rate, which reflected the oxygen supply level in each culture. The highest biomass, reaching 124.5g/L, was achieved under the highest OUR. DHA content was found to be highly correlated with the RQ value, and the highest DHA content (44.85% in total fatty acids, w/w) was achieved in the highest RQ level, which implies that the polyketide synthase pathway was more active. OUR and RQ, which reflect the physiological state of microorganisms, are suggested as synergistic real-time bioprocess monitoring parameters for DHA fermentation.

Improvement of L‐lactic acid production with a two‐step OUR control strategy

AbstractBACKGROUNDOxygen metabolism plays an important role in cell growth, metabolism and survival of microorganism. This report describes the effects of different oxygen metabolism levels on L‐lactic acid production by Lactobacillus paracasei, and then a new oxygen uptake rate (OUR) strategy is proposed based on integrated process physiological and metabolic analyses.RESULTSPhysiological parameter, OUR, was introduced to quantitatively characterize oxygen metabolism in a microaerobic bioprocess for the first time, and 0.14 mmol L−1 h−1 was adopted as control to simulate industrial lactic acid production. During the growth phase, moderate to high OUR (0.43 mmol L−1 h−1) could promote cell growth, glucose consumption and L‐lactic acid production with little decrease in yield. However, when cells entered the stationary phase, significant glycolysis inhibition and pyruvate metabolism shift from lactic acid to acetoin occurred with 0.43 and 0.85 mmol L−1 h−1, both of which led to further L‐lactic acid production limitation. Through a new two‐step OUR control strategy with 0.43 mmol L−1 h−1 during the growth phase and 0.14 mmol L−1 h−1 during the stationary phase, productivity was enhanced 12.7% and the same yield was achieved as in the control.CONCLUSIONSOUR was identified to be a feasible process control parameter for microaerobic lactic acid production, and the OUR control strategy efficiently improved L‐lactic acid production. © 2015 Society of Chemical Industry

Fish embryos on land: terrestrial embryo deposition lowers oxygen uptake without altering growth or survival in the amphibious fish Kryptolebias marmoratus.

Few teleost fishes incubate embryos out of water, but the oxygen-rich terrestrial environment could provide advantages for early growth and development. We tested the hypothesis that embryonic oxygen uptake is limited in aquatic environments relative to air using the self-fertilizing amphibious mangrove rivulus, Kryptolebias marmoratus, which typically inhabits hypoxic, water-filled crab burrows. We found that adult mangrove rivulus released twice as many embryos in terrestrial versus aquatic environments and that air-reared embryos had accelerated developmental rates. Surprisingly, air-reared embryos consumed 44% less oxygen and possessed larger yolk reserves, but attained the same mass, length and chorion thickness. Water-reared embryos moved their opercula ∼2.5 more times per minute compared with air-reared embryos at 7 days post-release, which probably contributed to the higher rates of oxygen uptake and yolk utilization we observed. Genetically identical air- and water-reared embryos from the same parent were raised to maturity, but the embryonic environment did not affect growth, reproduction or emersion ability in adults. Therefore, although aspects of early development were plastic, these early differences were not sustained into adulthood. Kryptolebias marmoratus embryos hatched out of water when exposed to aerial hypoxia. We conclude that exposure to a terrestrial environment reduces the energetic costs of development partly by reducing the necessity of embryonic movements to dispel stagnant boundary layers. Terrestrial incubation of young would be especially beneficial to amphibious fishes that occupy aquatic habitats of poor water quality, assuming low terrestrial predation and desiccation risks.