Times Higher Production Research Articles

Influence of Density of 3D Printing Using the Fdm Method on Productivity and Mechanical Properties of ABS

The economic and technical advantages of 3D printing make it a possible replacement for conventional production processes, especially for complex products and small batches. It is important to point out that technological parameters of 3D printing, such as layer thickness, print density, print speed, melting temperature, and table temperature, have a significant impact on the mechanical properties and productivity of parts obtained by 3D printing. Because of all the above, there is a great interest in research in this area. The paper presents the results of testing the tensile strength of the ABS polymer, in which two parameters were varied: the thickness of the print layer (0.39 mm) and the print density of 60–100% in steps of 10% each. The samples were obtained on a ZORTRAX M200+ 3D printer using fused filament deposition (FDM) technology. The selected thickness of the printing layer is relatively large, and with it, parts with lower accuracy and high surface roughness are obtained, although at the same time high productivity is achieved, which can satisfy some requirements. The obtained tensile strength values show that increasing the print density leads to an increase in its value, with a deviation in the sample with a print density of 100%, whereas the tensile strength values are comparable to the values obtained by other authors.

Assessing the Role and Capacity of Water Management Organizations for Ensuring Delta Food Security in Bangladesh

The coastal zone, consisting of one-third country's area, is the most climate-vulnerable region of Bangladesh. The country has invested significantly in coastal zone through the construction and rehabilitation of polders. Despite vast opportunities, land productivity in the polders is very low due to poor water governance and management. To improve in-polder water management, the responsibility of operation and maintenance of the polder water infrastructure has been transferred to Water Management Organizations (WMOs) since 2001. WMOs are currently voluntary organizations but are very important for micro-level agricultural water management. A study was conducted in 2017 and 2018 in a medium saline polder; with a major focus on organizational behaviour: hierarchy in decision-making, transparency, financial accountability, leadership, internal communication, and motivational incentives of the WMOs. The data were collected through a structured questionnaire from 192 respondents of randomly selected eight Water Management Groups (WMGs – the lowest tier of WMOs), out of 40 WMGs of the polder. The results revealed that the WMGs operations are not fully participatory in principle yet. Even the transparency, financial accountability, leadership, and internal communications within WMGs are not strong enough to take the organizational responsibility to address future challenges in food security of the climate-vulnerable polder communities. Improving drainage through efficient water management showed a yield gain of at least 1.5 t/ha in the wet season only. In addition, improved drainage fosters sustainable year-round cropping with high-yielding, high-value and nutrition-rich crops with 2 to 3 times higher productivity than the traditional cropping system. Therefore, investment in water governance particularly in improving drainage in the polders could be a major game-changer in sustaining the food security of the climate-vulnerable polder communities of Bangladesh. The study identified the knowledge gap as a significant concern that demands the need for capacity building of the WMOs.

Syntheses of Silylene-Bridged Thiophene-Fused Cyclopentadienyl ansa-Metallocene Complexes for Preparing High-Performance Supported Catalyst

We synthesized a series of Me2Si-bridged ansa-zirconocene complexes coordinated by thiophene-fused cyclopentadienyl and fluorenyl ligands (Me2Si(2-R1-3-R2-4,5-Me2C7S)(2,7-R32C13H6))ZrMe2 (R1 = Me or H, R2 = H or Me, R3 = H, tBu, or Cl) for the subsequent preparation of supported catalysts. We determined that the fluorenyl ligand adopts an η3-binding mode in 9 (R1 = Me, R2 = H, R3 = H) by X-ray crystallography. Further, we synthesized a derivative 15 by substituting the fluorenyl ligand in 9 with a 2-methyl-4-(4-tert-butylphenyl)indenyl ligand, derivatives 20 and 23 by substituting the Me2Si bridge in 12 (R1 = Me, R2 = H, R3 = tBu) and 15 with a tBuO(CH2)6(Me)Si bridge, and the dinuclear congener 26 by connecting two complexes with a –(Me)Si(CH2)6Si(Me)– spacer. The silica-supported catalysts prepared using 12, 20, and 26 demonstrated up to two times higher productivity in ethylene/1-hexene copolymerization than that prepared with conventional (THI)ZrCl2 (21–26 vs. 12 kg-PE/g-(supported catalyst)), producing polymers with comparable molecular weight (Mw, 330–370 vs. 300 kDa), at a higher 1-hexene content (1.3 vs. 1.0 mol%) but a lower bulk density of polymer particles (0.35 vs. 0.42 g/mL).

Impacts of elicitors on metabolite production and on antioxidant\xa0potential and tyrosinase inhibition in watercress microshoot cultures

The study has proved the stimulating effects of different strategies of treatments with elicitors on the production of glucosinolates (GSLs), flavonoids, polyphenols, saccharides, and photosynthetic pigments in watercress (Nasturtium officinale) microshoot cultures. The study also assessed antioxidant and anti-melanin activities. The following elicitors were tested: ethephon (ETH), methyl jasmonate (MeJA), sodium salicylate (NaSA), and yeast extract (YeE) and were added on day 10 of the growth period. Cultures not treated with the elicitor were used as control. The total GSL content estimations and UHPLC-DAD-MS/MS analyses showed that elicitation influenced the qualitative and quantitative profiles of GSLs. MeJA stimulated the production of gluconasturtiin (68.34 mg/100 g dried weight (DW)) and glucobrassicin (65.95 mg/100 g DW). The elicitation also increased flavonoid accumulation (max. 1131.33 mg/100 g DW, for 100 μM NaSA, collection after 24 h). The elicitors did not boost the total polyphenol content. NaSA at 100 μM increased the production of total chlorophyll a and b (5.7 times after 24 h of treatment), and 50 μM NaSA caused a 6.5 times higher production of carotenoids after 8 days of treatment. The antioxidant potential (assessed with the CUPRAC FRAP and DPPH assays) increased most after 24 h of treatment with 100 μM MeJA. The assessment of anti-melanin activities showed that the microshoot extracts were able to cause inhibition of tyrosinase (max. 27.84% for 1250 µg/mL).Key points• Elicitation stimulated of the metabolite production in N. officinale microshoots.• High production of pro-health glucosinolates and polyphenols was obtained.• N. officinale microshoots have got tyrosinase inhibition potential.• The antioxidant potential of N. officinale microshoots was evaluated.Graphical abstract

The Perfect Match: Adjusting High Tree Density to Rootstock Vigor for Improving Cropping and Land Use Efficiency of Sweet Orange

The rise in the productivity of sweet orange in Brazil has been related to the use of superior rootstocks and higher tree density, among other factors. In order to investigate whether the cropping system and the land use efficiency would benefit from more intensive cultivation, the performance of Valencia sweet orange was evaluated over nine years on four rootstocks, which induced contrasting vigor, at 513, 696 and 1000 trees·ha−1. Agronomic Institute of Campinas (IAC) 1697 and IAC 1710 citrandarins, and diploid and allotetraploid (4×) Swingle citrumelos were classified as semi-dwarfing, super-standard, standard, and dwarfing rootstocks, respectively. The fruit yield per tree was decreased at higher tree densities, notably for more vigorous rootstocks. Conversely, the cumulative productivity was increased over the evaluation period by 27% at 1000 trees·ha−1, irrespective of the rootstock, and the most vigorous rootstock resulted in 2.5 times higher production than the dwarfing one on average. Most fruit quality parameters were seldom influenced by the tree density, while the rootstock was a decisive factor in improving the quality and the soluble solids content. Dwarfing rootstocks allowed for harvesting 17% more fruit per minute by manual pickers. Because the tree row volume per area is lower with such rootstocks, even at higher tree density, spray volume can be reduced, although appropriate equipment should be developed for better spray coverage on smaller trees. Nine years after planting under strict vector control, the cumulative incidence of huanglongbing-symptomatic trees on IAC 1710 was double that on Swingle 4×. Taken together, the results suggested that the land use efficiency in the citrus industry can be further improved by planting vigorous rootstocks at moderate to high tree densities. Nevertheless, obtaining highly productive semi-dwarfing and dwarfing rootstocks is the sine qua non for making high-density pedestrian sweet orange orchards more profitable.

Tuning the gas-liquid-solid segmented flow for enhanced heterogeneous photosynthesis of Azo- compounds

Difficult handling the solid catalysts remains one of the pain points in the continuous flow photochemistry. In this work, the gas–liquid-solid segmented flow was employed in the photocatalytic production of azo- compounds (azoxybenzene and azobenzene) from nitrobenzene using graphitic carbon nitride (g-C3N4) as solid catalyst. Compared with the batch reactor, the photocatalytic reaction rate was greatly improved in the microreactor, and the reaction time was shortened from 180 min of the batch to 7.5 min for near-full conversion of nitrobenzene. The effects of various reaction parameters (temperature, light source power, catalyst content) in the continuous system were examined, and the reaction kinetic was found in first order. The photocatalytic reaction performance was very sensitive to the gas–liquid-solid segmented flow conditions, which needed to be carefully tuned. With the help of high-speed camera and micro particle image velocimetry (µ-PIV) techniques, it was identified that the increasing inert gas fraction resulted in more stable segmented flow with shorter liquid segments, favoring the reaction rate. With a high gas fraction, the intensity of recirculation in the liquid segments was strengthened by the increasing total flow rate, enhancing the local mass transfer, thereby benefiting the photocatalytic reaction. Overall, the continuous microreactor reached 5.6 times higher productivity per volume (26.1 mmol/h*L) of azo- compounds than the batch reactor under the same conditions. The successful photosynthesis of azo- compounds demonstrated the great potential of the presented gas–liquid-solid segmented flow, and the findings of this work provide useful guidance on its future application in other heterogeneously catalyzed reactions.

Establishment of genomic library technology mediated by non-homologous end joining mechanism in Yarrowia lipolytica.

Genomic variants libraries are conducive to obtain dominant strains with desirable phenotypic traits. The non-homologous end joining (NHEJ), which enables foreign DNA fragments to be randomly integrated into different chromosomal sites, shows prominent capability in genomic libraries construction. In this study, we established an efficient NHEJ-mediated genomic library technology in Yarrowia lipolytica through regulation of NHEJ repair process, employment of defective Ura marker and optimization of iterative transformations, which enhanced genes integration efficiency by 4.67, 22.74 and 1.87 times, respectively. We further applied this technology to create high lycopene producing strains by multi-integration of heterologous genes of CrtE, CrtB and CrtI, with 23.8 times higher production than rDNA integration through homologous recombination (HR). The NHEJ-mediated genomic library technology also achieved random and scattered integration of loxP and vox sites, with the copy number up to 65 and 53, respectively, creating potential for further application of recombinase mediated genome rearrangement in Y. lipolytica. This work provides a high-efficient NHEJ-mediated genomic library technology, which enables random and scattered genomic integration of multiple heterologous fragments and rapid generation of diverse strains with superior phenotypes within 96 h. This novel technology also lays an excellent foundation for the development of other genetic technologies in Y. lipolytica.

New Insights into the Deactivation and Stabilization Causes of Plugged AlSBA‐15 in Liquid‐phase Friedel‐Crafts Organic Reactions

AbstractDeactivation is the major challenge of heteroatom‐substituted mesoporous silica materials for large scale applications. Here we report the impact of plugging of mesochannels of AlSBA‐15 on activity and stability of liquid‐phase acylation of anisole with (extremely) low catalyst loadings of 0.15–0.6 wt.% and 0.6–3 wt.% in batch and in repeated batch reactions, respectively. The analysis of property‐catalytic performances showed that deactivation of the plugged AlSBA‐15 was partially from a physical cause by deposition of a uniform nanometer layer of coke on the surface blocking the active sites which could be restored by calcination and partially from an irreversible chemical cause by Al leaching. The catalytic performance of plugged AlSBA‐15 was compared with that of open AlSBA‐[15]. The plugged AlSBA‐15 showed lower but more sustained activity than that by open AlSBA‐15 coming from less and different type of coke deposition. These properties of plugged AlSBA‐15 resulted in two times higher productivity (44.3 vs 23.3 mg‐product/mg‐catalyst) than that by open AlSBA‐[15] . The plugging of mesochannels thus reduced the amount of coke deposition and stabilized the catalyst; however, it exerted no effect on Al leaching. In conclusion, understanding the role of plugging of mesochannels in stabilization and Al leaching and coke deposition in deactivation are useful to design and synthesize efficient solid acid catalysts for liquid‐phase organic reactions.

Non-destructive extraction of lipids from Botryococcus braunii and its potential to reduce pond area and nutrient costs

The production of oil from microalgae is a process with a long way to go before reaching commercial viability. High costs associated with harvesting and solvent extraction make it difficult to compete with fossil fuel. The in-situ, non-destructive, repetitive extraction of lipids from Botryococcus braunii (milking) offers an alternative to the conventional microalgal-oil production process, with significantly reduced nutrient, dewatering and cultivation costs. Here, we compare low shear column solvent extraction with high shear stirred tank solvent extraction to ascertain which is better suited to a repetitive extraction process using B. braunii and carry out a preliminary economic analysis on the nutrient costs and raceway pond area requirements once scaled to industrial production. Stirred tank extraction with heptane resulted in five times higher productivities than that of column solvent extraction. Using this to generate an extraction model we found a lipid productivity of 104 mg L-1 day-1 was possible, six times greater than that of previous repetitive extraction studies. Thanks to the high lipid content of the B. braunii biomass generated in the recovery phase, when scaled to open raceway ponds, a lipid productivity of 13.4 g m-2 day-1 can be predicted. With this productivity, an estimated combined carbon, nitrogen and phosphorus cost of $2.52 L-1 of oil produced and a cultivation pond area of 3.53 km2 (assuming an annual oil production of 15,900 m3 year-1) is predicted, corresponding to reductions when compared to conventional extraction of 40% and 50% respectively. This repetitive extraction process provides an alternative method for the production of 3rd generation biofuels without the need to harvest and dewater algal biomass with significant reductions in nutrient and pond area requirements.

Recent Contributions of Some Fields of the Electronics in Development of Forest Operations Technologies

In the last years, there has been a growing need to improve forest-wood chain concerning all three pillars of sustainability (economic, environmental, and social). Using electronic systems, in particular GIS, GNSS, and various kinds of sensors related to forest harvesting, is clearly one of the most powerful instruments to reach this aim. The contribution of these tools to forest operation is wide and various. One of the most important application was integrating ICT and GPS/GNSS on-board systems on modern forest machines. This allowed one to ensure multiple benefits to forest operation field. On the one hand, electronic systems, and particularly GIS, could be used to improve forest harvesting with a previous planning of the skid trails network, in order to minimize utilization impacts and risks for operators, ensuring at the same time high work productivity. Moreover, GIS developed files could also be implemented in modern forest machine GPS/GNSS systems, helping forest machines operators to move only along a designed skid trails network or making it possible to avoid restricted access areas. On the other hand, modern forest machines could be equipped with complex and accurate sensors that are able to determine, register, and share information about wood biomass quantity and quality and even undertake economic evaluation of stumpage value. Finally, the input and output of these systems and sensors could be implemented in a decision support system (DSS) ensuring the best silvicultural and operative alternative from a sustainable forest management point of view. A detailed review of the contribution of electronics in the development of forest operations is provided here.

FeedER: a feedback-regulated enzyme-based slow-release system for fed-batch cultivation in microtiter plates

With the advent of modern genetic engineering methods, microcultivation systems have become increasingly important tools for accelerated strain phenotyping and bioprocess engineering. While these systems offer sophisticated capabilities to screen batch processes, they lack the ability to realize fed-batch processes, which are used more frequently in industrial bioprocessing. In this study, a novel approach to realize a feedback-regulated enzyme-based slow-release system (FeedER), allowing exponential fed-batch for microscale cultivations, was realized by extending our existing Mini Pilot Plant technology with a customized process control system. By continuously comparing the experimental growth rates with predefined set points, the automated dosage of Amyloglucosidase enzyme for the cleavage of dextrin polymers into d-glucose monomers is triggered. As a prerequisite for stable fed-batch operation, a constant pH is maintained by automated addition of ammonium hydroxide. We show the successful application of FeedER to study fed-batch growth of different industrial model organisms including Corynebacterium glutamicum, Pichia pastoris, and Escherichia coli. Moreover, the comparative analysis of a C. glutamicum GFP producer strain, cultivated under microscale batch and fed-batch conditions, revealed two times higher product yields under slow growing fed-batch operation. In summary, FeedER enables to run 48 parallel fed-batch experiments in an automated and miniaturized manner, and thereby accelerates industrial bioprocess development at the screening stage.

Optimization of limonene biotransformation to limonene-1,2-diol by Colletotrichum nymphaeae CBMAI 0864

Abstract This study aimed to optimize the conditions of the biotransformation of limonene to limonene-1,2-diol by C. nymphaeae. In the initial modeling, in shake flasks, the use of 13.2 g.L−1 biomass, 27 °C, 250 rpm, and pH of 6.0 could maximize the production of limonene-1,2-diol (6.75 g.L−1). Subsequently, optimal conditions were transposed to a bioreactor, where agitation and aeration were also evaluated. A minimum 60% of dissolved oxygen was defined for this process. The limonene volatilization could be reduced almost three times when a larger condenser is used. Finally, when the bioreactor was operated at 27 °C, 300 rpm, 1 vvm, and with 13.2 g.L−1 biomass, limonene-1,2-diol production reached 7.1, 7.8, and 5.6 g.L−1 after 72 h when using 20 g.L−1 of R-(+)-, S-(−)-limonene or citrus terpene as substrate, respectively. This is approximately the same maximum product concentration found for the shake flasks, but it represents an almost three times higher productivity.

An indoor pelagic mesocosm facility to simulate multiple water-column characteristics

Mesocosms are important research tools in aquatic ecology because they close the gap between laboratory studies at the individual or lower organization level and field studies at the population and ecosystem level. However, most mesocosm studies regarding the pelagic environment do not consider the effects of physical factors like water-column stratification, turbulence and mixing. Neglecting such factors might bias the results compared to the natural system. Using a unique indoor mesocosm facility, we present results on how different water-column stratifications can be made and how they act as barriers for exchange between water layers. Turbulent mixing, simulated by vertically rotating incubation vessels, is shown to be of high importance for primary production, generating up to nine times higher production in humus-rich water than incubation vessels at fixed depths. Convective stirring is shown to be an attractive method for generating different turbulence conditions, and different temperature settings can be used to get turnover times from 84 h or more down to 17 min for a 5-m water parcel. We also demonstrate how an anoxic bottom layer can be achieved by stimulating heterotrophic bacteria through addition of bioavailable organic carbon.

Continuous precipitation of process related impurities from clarified cell culture supernatant using a novel coiled flow inversion reactor (CFIR).

Coiled Flow Inverter Reactor (CFIR) has recently been explored for facilitating continuous operation of several unit operations involved in downstream processing of biopharmaceuticals such as viral inactivation and protein refolding. The application of CFIR for continuous precipitation of clarified cell culture supernatant has been explored. The pH based precipitation is optimized in the batch mode and then in the continuous mode in CFIR using a design of experiments (DOE) study. Improved clearance of host cell DNA (52× vs. 39× in batch), improved clearance of host cell proteins (HCP) (7× vs. 6× in batch) and comparable recovery (90 vs. 91.5 % in batch) are observed along with six times higher productivity. To further demonstrate wider applicability of CFIR in performing continuous precipitation, two more case studies involving use of two different precipitation protocols (CaCl2 based and caprylic acid based) are also performed. In both cases, clearance of host cell DNA, HCP, and product recovery are found to be comparable or better in CFIR than in batch operations. Moreover, increase in productivity of 16 times (CaCl2 based) and eight times (caprylic acid based) is obtained for the two precipitation protocols, respectively. The data clearly demonstrate that CFIR can be seamlessly integrated into a continuous bioprocess train for performing continuous precipitation of clarified cell culture supernatant. To our knowledge this is the first report of such use.

Efficient and Selectable Production of Reactive Species Using a Nanosecond Pulsed Discharge in Gas Bubbles in Liquid

A plasma gas bubble‐in‐liquid method for high production of selectable reactive species using a nanosecond pulse generator has been developed. The gas of choice is fed through a hollow needle in a point‐to‐plate bubble discharge, enabling improved selection of reactive species. The increased interface reactions, between the gas‐plasma and water through bubbles, give higher productivity. H2O2 was the predominant species produced using Ar plasma, while predominantly and NO2 were generated using air plasma, in good agreement with the observed emission spectra. This method has nearly 100% selectivity for H2O2, with seven times higher production, and 92% selectivity for , with nearly twice the production, compared with a plasma above the water.

Brevibacillus themoruber : a promising microbial cell factory for exopolysaccharide production

This study aims to identify a high level exopolysaccharide (EPS) producer thermophile that in turn could be used as a model organism to study the biological mechanisms and whole genome organization of EPS-producing thermophilic bacteria. Thermophilic isolates were screened, and then growth and EPS production of the best producer Brevibacillus thermoruber strain 423 were investigated under different carbon and nitrogen sources, temperature, pH and agitation rates. Rheological characterization revealed that the EPS behaved like a typical Newtonian fluid and viscosity of the EPS solution increased with increasing Ca(2+) ion concentration. Chemical characterization by TLC, GC-MS, FT-IR and NMR suggested a heteropolymer structure with glucose as major monomer unit. High biocompatibility of pure EPS fractions suggested their potential use in biomedical applications. This study reports on the comprehensive description of microbial production conditions as well as chemical, rheological and biological characterization of the EPS produced by B. thermoruber strain 423. The bioreactor cultures were found to reach two times higher yields and three times higher productivities when compared with literature. Brevibacillus thermoruber strain 423 combined the advantages of its nonpathogenicity with the advantages of fast productivity and hence proved to be a very promising model organism and cell factory for microbial EPS production.

Comparison of growth of Tetraselmis in a tubular photobioreactor (Biocoil) and a raceway pond

Microalgae cultivation systems can be divided broadly into open ponds and closed photobioreactors. This study investigated the growth and biomass productivity of the halophilic green alga Tetraselmis sp. MUR-233, grown outdoors in paddle wheel-driven open raceway ponds and in a tubular closed photobioreactor (Biocoil) at a salinity of 7 % NaCl (w/v) between mid-March and June 2010 (austral autumn/winter). Volumetric productivity in the Biocoil averaged 67 mg ash-free dry weight (AFDW) L−1 day−1 when the culture was grown without CO2 addition. This productivity was 86 % greater, although less stable, than that achieved in the open raceway pond (36 mg L−1 day−1) grown at the same time in the autumn period. The Tetraselmis culture in the open raceway pond could be maintained in semi-continuous culture for the whole experimental period of 3 months without an additional CO2 supply, whereas in the Biocoil, under the same conditions, reliable semi-continuous culture was only achievable for a period of 38 days. However, stable semi-continuous culture was achieved in the Biocoil by the addition of CO2 at a controlled pH of ~7.5. With CO2 addition, the volumetric biomass productivity in the Biocoil was 85 mg AFDW L−1 day−1 which was 5.5 times higher than the productivity achieved in the open raceway pond (15 mg AFDW L−1 day−1) with CO2 addition and 8 times higher compared to the productivity in the open raceway pond without CO2 addition (11 mg AFDW L−1 day−1), when cultures were grown in winter. The illuminated area productivities highlight an alternative story and showed that the open raceway pond had a three times higher productivity (3,000 mg AFDW m−2 day−1) compared to the Biocoil (850 mg AFDW m−2 day−1). Although significant differences were found between treatments and cultivation systems, the overall average lipid content for Tetraselmis sp. MUR-233 was 50 % in exponential phase during semi-continuous cultivation.

Intensification of enzymatic conversion of glucose to lactic acid by reactive extraction

Lactic acid is an important commercial product and extracting this out of aqueous solution is a growing requirement in fermentation-based industries and recovery from waste streams. The design of an amine extraction process requires (i) equilibrium and (ii) kinetic data for the acid–amine (solvent) system used. Equilibria and kinetics for lactic acid extraction by Alamine 336 in octanol as a diluent have been determined and compared with other diluents studied earlier. An approach for extracting the lactic acid by a long-chain tertiary amine, which is in the dispersed phase as a liquid ion exchanger (LIX), is presented. A mathematical model for slurry phase reactor with glucose in the continuous aqueous phase, the amine with a diluent in the dispersed phase and the immobilized enzyme as the solid catalyst, has been developed using equilibrium and kinetic data for reactive extraction. Effects of various parameters affecting the conversion of glucose have been discussed. The model has been solved for batch and semi-batch modes. It has been shown that the semi-batch mode yields approximately five times higher productivity than batch mode.

Site-specific mutagenesis at positions 272 and 273 of the Bacillus sp. SAM1606 α-glucosidase to screen mutants with altered specificity for oligosaccharide production by transglucosylation

The Bacillus sp. SAM1606 α-glucosidase catalyzes the transglucosylation of sucrose to produce theanderose (6- O G-glucosylsucrose) as the major transfer product along with the other di-, tri-, and tetrasaccharides. To obtain an α-glucosidase variant(s) producing theanderose more abundantly, we carried out site-specific mutagenesis studies, in which an amino acid residue (Gly273 or Thr272) near the putative catalytic site (Glu271) of this α-glucosidase was replaced by all other naturally-occurring amino acids. Each mutant, whose concentration was set at 2.6 U/ml (sucrose-hydrolyzing units), was reacted at 60 °C and pH 6.0 with 1.75 M sucrose, and the course of the oligosaccharide production was monitored by HPLC to systematically analyze the effects of amino acid substitutions on the specificity of transglucosylation. The analysis clearly showed site- and residue-dependent differential effects of substitution near the catalytic site on the specificity of oligosaccharide production. For example, mutants with substitution at position 273 by aromatic amino acids or His virtually lost the ability to produce oligosaccharides by transglucosylation. Mutants with substitution at position 272 by amino acids that were bulkier than the wild-type Thr showed enhanced production of tetrasaccharides; whereas, mutants with substitution at position 273 by Lys and Arg exclusively produced disaccharidal transfer products. The highest specificity for theanderose formation (i.e. the highest content of theanderose in the reaction product) was obtained with the T272I mutant, which showed 1.74 times higher productivity (per sucrose-hydrolyzing unit) of theanderose than that of the wild-type enzyme.

Physical control of primary productivity on a seasonal scale in central and eastern Arabian Sea

Usingin situ data collected during 1992–1997, under the Indian programme of Joint Global Ocean Flux Study (JGOFS), we show that the biological productivity of the Arabian Sea is tightly coupled to the physical forcing mediated through nutrient availability. The Arabian Sea becomes productive in summer not only along the coastal regions of Somalia, Arabia and southern parts of the west coast of India due to coastal upwelling but also in the open waters of the central region. The open waters in the north are fertilized by a combination of divergence driven by cyclonic wind stress curl to the north of the Findlater Jet and lateral advection of nutrient-rich upwelled waters from Arabia. Productivity in the southern part of the central Arabian Sea, on the other hand, is driven by advection from the Somalia upwelling. Surface cooling and convection resulting from reduced solar radiation and increased evaporation make the northern region productive in winter. During both spring and fall inter-monsoons, this sea remains warm and stratified with low production as surface waters are oligotrophic. Inter-annual variability in physical forcing during winter resulted in one-and-a-half times higher production in 1997 than in 1995.