title: A Rapid, Small-Scale Method for Improving Fermentation Medium Performance

authors: Zhu, Yin

subjects: media design

abstract: Cell biomass and chemicals (e.g. bioactive compounds) can be produced by fermentation.  Optimising a fermentation system involves optimizing many variables such as determining the effect of inoculum quality and media components, and selecting the most appropriate fermenter design and operating conditions (such as agitation aeration and fermentation mode).  Identifying the optimal media is very important because it can significantly affect product concentration, yield and productivity.  However, the media contains many components so many trials need to be done, which makes the process laborious, expensive, open-ended, and often time-consuming.  The data generated from the many trials can be difficult to analyse.  

This study developed a rapid, inexpensive small-scale technique to identify how media components affected the growth of Streptomyces hygroscopicus and its production of a secondary metabolite, the anti-tumour agent rapamycin.  A method was developed using microtitre plates to screen the effect of three concentrations of nine media components on cell growth and rapamycin production using the Box-Behnken experimental design.  Firstly, the methodology for microtitre plates was developed, which involved characterizing the physical parameters of a fermentation system, identifying the incubation time to minimize evaporation, modifying the assay method to deal with the small sample volumes, and developing an alternative method to determinate the rapamycin concentration that was cheaper than the HPLC method.  Data from shake flasks trials (the normal screening method) were used to validate the microtitre method and to assess the latter's usefulness in predicting scale-up effects.

Six media components - sodium chloride (NaCl), di-potassium orthophosphate (K2HPO4), l-aspartic acid, l-arginine, l-histidine and salt (formula 1) solution - significantly affected culture growth and/or rapamycin concentration.  The regression tree method was used to indicate the importance and critical concentration range of each factor.  The Pearson's product-moment value indicated a good correlation between data from microtitre plates and shake flasks (cell growth: r=0.75 p=0.016 n=8; rapamycin concentration r=0.92 p=0.08 n=6).  

The speed of the microtitre plate and shake methods were compared by assessing the total cycle time and the time required for various stages in the method.  Performance of each method was assessed as cost of media and equipment.  Using microtitre plates to screen and optimise media in terms of biomass and secondary metabolite production is faster and cheaper than using shake flasks.  Labour efficiency for the numerous, repetitive, small-scale experiments was substantially increased.  Trials could be run without well-to-well cross contamination.  

The  regression tree  statistics methodology successfully showed the effect of input variables on target variables and identified effective medium component concentrations and any interactions.  It is recommended that the microtitre plate procedure developed in this research may be applied to any study investigating the optimum media composition for growing other Streptomyces spp. strains, in screening studies when searching for new bioactive molecules, or for characterizing natural or recombinant/mutated micro-organisms.

text: A Rapid, Small-Scale Method for Improving Fermentation Medium Performance Cell biomass and chemicals (e.g. bioactive compounds) can be produced by fermentation.  Optimising a fermentation system involves optimizing many variables such as determining the effect of inoculum quality and media components, and selecting the most appropriate fermenter design and operating conditions (such as agitation aeration and fermentation mode).  Identifying the optimal media is very important because it can significantly affect product concentration, yield and productivity.  However, the media contains many components so many trials need to be done, which makes the process laborious, expensive, open-ended, and often time-consuming.  The data generated from the many trials can be difficult to analyse.  

This study developed a rapid, inexpensive small-scale technique to identify how media components affected the growth of Streptomyces hygroscopicus and its production of a secondary metabolite, the anti-tumour agent rapamycin.  A method was developed using microtitre plates to screen the effect of three concentrations of nine media components on cell growth and rapamycin production using the Box-Behnken experimental design.  Firstly, the methodology for microtitre plates was developed, which involved characterizing the physical parameters of a fermentation system, identifying the incubation time to minimize evaporation, modifying the assay method to deal with the small sample volumes, and developing an alternative method to determinate the rapamycin concentration that was cheaper than the HPLC method.  Data from shake flasks trials (the normal screening method) were used to validate the microtitre method and to assess the latter's usefulness in predicting scale-up effects.

Six media components - sodium chloride (NaCl), di-potassium orthophosphate (K2HPO4), l-aspartic acid, l-arginine, l-histidine and salt (formula 1) solution - significantly affected culture growth and/or rapamycin concentration.  The regression tree method was used to indicate the importance and critical concentration range of each factor.  The Pearson's product-moment value indicated a good correlation between data from microtitre plates and shake flasks (cell growth: r=0.75 p=0.016 n=8; rapamycin concentration r=0.92 p=0.08 n=6).  

The speed of the microtitre plate and shake methods were compared by assessing the total cycle time and the time required for various stages in the method.  Performance of each method was assessed as cost of media and equipment.  Using microtitre plates to screen and optimise media in terms of biomass and secondary metabolite production is faster and cheaper than using shake flasks.  Labour efficiency for the numerous, repetitive, small-scale experiments was substantially increased.  Trials could be run without well-to-well cross contamination.  

The  regression tree  statistics methodology successfully showed the effect of input variables on target variables and identified effective medium component concentrations and any interactions.  It is recommended that the microtitre plate procedure developed in this research may be applied to any study investigating the optimum media composition for growing other Streptomyces spp. strains, in screening studies when searching for new bioactive molecules, or for characterizing natural or recombinant/mutated micro-organisms.

year: 2007

title: Mechanical and Structural Properties of Microwave Sintered Tin-Copper-Antimony Alloys

authors: Ariff, Tasnim Firdaus Binti Mohamed

subjects: Pewter alloys

abstract: Tin-copper-antimony (pewter) alloys have been traditionally produced by a casting process which consumes large amounts of energy, time and as a result is expensive. This research aims to investigate the possibilities of implementing powder metallurgy for pewter production through a sintering process using microwave energy. The optimum sintering conditions using microwave sintering are also of interest. Pewter alloys were examined to determine the effect of green density, sintering time, and sintering temperature on the mechanical and structural properties of the sintered compacts. Samples were prepared by hydraulic pressing of a well mixed and blended tin alloy powder with three different compositions; 97wt%Sn 2wt%Cu 1wt%Sb, 94wt%Sn 4wt%Cu 2wt%Sb and 91wt%Sn 6wt%Cu 3wt%Sb. Two compaction loads were used to produce the samples with different green densities. Pellets pressed at 96 MPa had an average relative density of 80.7%, while those pressed at 129 MPa had an average green density of 84.6%.  

Sixteen different time-temperature combinations were used for the heat treatments at 160 and 220 C for both conventional and microwave sintering. However, the sintering times had to be restricted to 15 and 30 minutes for microwave heating. Meanwhile, 60 and 120 minutes were used for conventional heating. It was found that for all three compositions, samples with a higher green density had a higher sintered density, compared to samples with lower green density, for the same sintering time and temperature. The relative density of sintered pewter alloys increased on average by 13% after conventional sintering and by about 14% after microwave sintering, when the sintering was carried out for the longer of the two sintering times and at the higher of the sintering temperatures selected, for all three compositions. 

Moreover, the hardness increased by 25.6%, 23.5% and 7.0% when microwave sintered relative to the conventional sintering for 97Sn2Cu1Sb, 94Sn4Cu2Sb and 91Sn6Cu3Sb alloys respectively. Nevertheless, the grain size remained similar for all three compositions under the same sintering conditions. The degree of grain growth in microwave sintered samples was marginally smaller (up to 23-24 μm) than in conventionally sintered samples which reached a grain size of 26-27 μm. 

In terms of strength, microwave sintering produced samples with similar properties to those conventionally sintered under the same sintering conditions for all three compositions. The tensile strengths obtained compared well with the strengths obtained from the casting process. Nonetheless, tensile strengths for both conventionally and microwave sintered material was higher in the transverse direction than in the longitudinal direction. In conventionally sintered material, there was an increase in transverse strength of about 6.9%, 5% and 4%, while for the microwave sintered material, the strength increase was 9.1%, 5.6% and 4.5% for 97Sn2Cu1Sb, 94Sn4Cu2Sb and 91Sn6Cu3Sb alloys respectively when compared to the longitudinal direction. 

The microwave sintered samples in general have improved hardness, better densification and a finer microstructure compared with the conventionally sintered samples and traditionally cast pewter. Increasing the Cu and Sb content increases the hardness and strength but in return, decreases its ductility. Hence, a pewter alloy with a moderate amount of Cu and Sb, i.e. 97Sn2Cu1Sb, microwave sintered at 220 C for 30 minutes would be the best choice for optimum mechanical properties.

text: Mechanical and Structural Properties of Microwave Sintered Tin-Copper-Antimony Alloys Tin-copper-antimony (pewter) alloys have been traditionally produced by a casting process which consumes large amounts of energy, time and as a result is expensive. This research aims to investigate the possibilities of implementing powder metallurgy for pewter production through a sintering process using microwave energy. The optimum sintering conditions using microwave sintering are also of interest. Pewter alloys were examined to determine the effect of green density, sintering time, and sintering temperature on the mechanical and structural properties of the sintered compacts. Samples were prepared by hydraulic pressing of a well mixed and blended tin alloy powder with three different compositions; 97wt%Sn 2wt%Cu 1wt%Sb, 94wt%Sn 4wt%Cu 2wt%Sb and 91wt%Sn 6wt%Cu 3wt%Sb. Two compaction loads were used to produce the samples with different green densities. Pellets pressed at 96 MPa had an average relative density of 80.7%, while those pressed at 129 MPa had an average green density of 84.6%.  

Sixteen different time-temperature combinations were used for the heat treatments at 160 and 220 C for both conventional and microwave sintering. However, the sintering times had to be restricted to 15 and 30 minutes for microwave heating. Meanwhile, 60 and 120 minutes were used for conventional heating. It was found that for all three compositions, samples with a higher green density had a higher sintered density, compared to samples with lower green density, for the same sintering time and temperature. The relative density of sintered pewter alloys increased on average by 13% after conventional sintering and by about 14% after microwave sintering, when the sintering was carried out for the longer of the two sintering times and at the higher of the sintering temperatures selected, for all three compositions. 

Moreover, the hardness increased by 25.6%, 23.5% and 7.0% when microwave sintered relative to the conventional sintering for 97Sn2Cu1Sb, 94Sn4Cu2Sb and 91Sn6Cu3Sb alloys respectively. Nevertheless, the grain size remained similar for all three compositions under the same sintering conditions. The degree of grain growth in microwave sintered samples was marginally smaller (up to 23-24 μm) than in conventionally sintered samples which reached a grain size of 26-27 μm. 

In terms of strength, microwave sintering produced samples with similar properties to those conventionally sintered under the same sintering conditions for all three compositions. The tensile strengths obtained compared well with the strengths obtained from the casting process. Nonetheless, tensile strengths for both conventionally and microwave sintered material was higher in the transverse direction than in the longitudinal direction. In conventionally sintered material, there was an increase in transverse strength of about 6.9%, 5% and 4%, while for the microwave sintered material, the strength increase was 9.1%, 5.6% and 4.5% for 97Sn2Cu1Sb, 94Sn4Cu2Sb and 91Sn6Cu3Sb alloys respectively when compared to the longitudinal direction. 

The microwave sintered samples in general have improved hardness, better densification and a finer microstructure compared with the conventionally sintered samples and traditionally cast pewter. Increasing the Cu and Sb content increases the hardness and strength but in return, decreases its ductility. Hence, a pewter alloy with a moderate amount of Cu and Sb, i.e. 97Sn2Cu1Sb, microwave sintered at 220 C for 30 minutes would be the best choice for optimum mechanical properties.

year: 2009

title: Maori goddesses in literature. Part 2: 1900-1940

authors: Yates-Smith, Aroha

subjects: Atua wāhine

abstract: Many contemporary Māori are familiar with atua wāhine, Māori goddesses, through accounts that have been passed on to them by word of mouth. Few, however, have had an opportunity to consult accounts of atua wāhine that date from the early period of Māori-Pākehā contact. Those who wish to do so may have considerable difficulty in sifting through all of the written materials for the information they seek. For this reason, this paper provides a review of the literature pertaining to atua wāhine from 1900 to 1940, together with a commentary on the sources to which reference is made. A review of literature on atua wāhine from 1880 – 1900 appeared in the first issue of this Journal. The period 1940 towards 2000 will be reviewed in the next issue.

text: Maori goddesses in literature. Part 2: 1900-1940 Many contemporary Māori are familiar with atua wāhine, Māori goddesses, through accounts that have been passed on to them by word of mouth. Few, however, have had an opportunity to consult accounts of atua wāhine that date from the early period of Māori-Pākehā contact. Those who wish to do so may have considerable difficulty in sifting through all of the written materials for the information they seek. For this reason, this paper provides a review of the literature pertaining to atua wāhine from 1900 to 1940, together with a commentary on the sources to which reference is made. A review of literature on atua wāhine from 1880 – 1900 appeared in the first issue of this Journal. The period 1940 towards 2000 will be reviewed in the next issue.

year: 2001-02