title: Post-transcriptional modulation of the SigF regulon inMycobacterium smegmatisby the PhoH2 toxin-antitoxin

authors: Andrews, Emma Sophie Vout

subjects: Science & Technology

abstract: PhoH2 proteins are highly conserved across bacteria and archaea yet their biological function is poorly characterised. We examined the growth profiles of Mycobacterium smegmatis strains mc²155 and mc²155 ΔphoH2 and observed the same growth profile and growth rate in a variety of conditions. In light of the comparable growth, we used RNAseq to provide a snapshot of the differences between the transcriptomes of M. smegmatis mc²155 and M. smegmatis mc²155 ΔphoH2 during normal growth. At 48 hours, elevated expression of the sigF regulon was observed in ΔphoH2 relative to wild type. In biochemical assays, PhoH2 showed activity toward sigF mRNA insinuating a role of PhoH2 in modulating the pool of sigF mRNA in the cell during normal growth, adding further complexity to the repertoire of reported mechanisms of post-translational regulation. Multiple copies of the preferred target site of PhoH2 were identified in loops of the sigF mRNA structure, leading us to propose a mechanism for the activity of PhoH2 that is initiated after assembly on specific single-stranded loops of RNA. We hypothesise that PhoH2 is a toxin-antitoxin that contributes to the regulation of SigF at a post-transcriptional level through targeted activity on sigF mRNA. This work presents the first evidence for post-transcriptional regulation of SigF along with the biological function of PhoH2 from M. smegmatis. This has implications for the highly conserved PhoH2 toxin-antitoxin module across the mycobacteria including the important human pathogen M. tuberculosis.

text: Post-transcriptional modulation of the SigF regulon inMycobacterium smegmatisby the PhoH2 toxin-antitoxin PhoH2 proteins are highly conserved across bacteria and archaea yet their biological function is poorly characterised. We examined the growth profiles of Mycobacterium smegmatis strains mc²155 and mc²155 ΔphoH2 and observed the same growth profile and growth rate in a variety of conditions. In light of the comparable growth, we used RNAseq to provide a snapshot of the differences between the transcriptomes of M. smegmatis mc²155 and M. smegmatis mc²155 ΔphoH2 during normal growth. At 48 hours, elevated expression of the sigF regulon was observed in ΔphoH2 relative to wild type. In biochemical assays, PhoH2 showed activity toward sigF mRNA insinuating a role of PhoH2 in modulating the pool of sigF mRNA in the cell during normal growth, adding further complexity to the repertoire of reported mechanisms of post-translational regulation. Multiple copies of the preferred target site of PhoH2 were identified in loops of the sigF mRNA structure, leading us to propose a mechanism for the activity of PhoH2 that is initiated after assembly on specific single-stranded loops of RNA. We hypothesise that PhoH2 is a toxin-antitoxin that contributes to the regulation of SigF at a post-transcriptional level through targeted activity on sigF mRNA. This work presents the first evidence for post-transcriptional regulation of SigF along with the biological function of PhoH2 from M. smegmatis. This has implications for the highly conserved PhoH2 toxin-antitoxin module across the mycobacteria including the important human pathogen M. tuberculosis.

year: 2020

title: Synthesis, Microstructure and Mechanical Properties of Titanium with Controlled Levels of Porosity

authors: Xu, Qian

subjects: Titanium

abstract: Porous titanium (Ti) products have many applications due to their excellent corrosion resistance, high strength-to-weight ratio, high specific surface area, etc. However, the major limitation is the expensive cost of porous Ti products because of the high raw materials costs and the difficulty of processing. The novelty of this research work is concerned with a study of a ceramic casting technique, slip casting, to create porous Ti products and the effect of porosity on the mechanical properties and gas permeability of Ti compacts. 

An optimised Ti slurry was developed from 43 vol.% of Ti powder, 0.3 dw.% of dispersant, 0.8 dw.% of plasticiser and 0.8 dw.% of binder, mixed with a balance of distilled water, which produced a viscosity of 290 cP. It was then poured into a plaster mould to form compacts with a green density of 45%. Thermal debinding was carried out at 320°C with an argon flow for 2 hours, followed by vacuum sintering different samples at 1000°C and 1200°C for 0.5 hours, respectively. The porous sintered compacts had satisfactory tensile strength with some plastic deformation. The increase in oxygen and carbon content during processing was minor. The results from this investigation suggested that slip casting is a potentially low-cost, simple manufacturing route for porous Ti products.

Porous Ti compacts with porosity in the range of 12.3 vol.% to 35.3 vol.% were fabricated by slip casting. The mechanical properties, fracture morphology, gas permeability, pore size analysis and pore shape factors for the porous Ti compacts were determined for different porosity levels. A decreasing porosity level resulted in less open porosity and gas permeability, reduced pore size, and an increased tensile stress and elongation. The mechanical properties of porous Ti compacts produced by slip casting were comparable with more conventional press and sintered materials at the same porosity levels. Theoretical models for tensile stress and ductility as a function of porosity were examined and incorporated into the results and differences between the theoretical models and experimental results are discussed. The pore shape factor analysis showed that tensile loading would stretch the pores in the compacts to produce more irregular pores, which were acting as linkage sites to allow the propagation of cracks. Additionally, a novel interconnected pore characterisation method using ammonium meta-tungstate solution is presented. By using backscatter scanning electron microscopy, the interconnected pores can be directly observed. 

The packing behaviour and sintering behaviour of Ti compacts fabricated with different particles size distribution were characterised and studied, in terms of porosity, pore size analysis, tensile properties and gas permeability. Two different particles size (avg. 14 μm & avg. 56 μm) of pure Ti hydride-dehydride powder were used in five volume proportions (20:80, 40:60, 60:40, 80:20 & 100:0). A theoretical model predicted that the green density reaches a maximum when the volume fraction of fine particles is 0.35. It was found that although experimental results showed similar behaviour there was no well-defined maximum green density. The sintered compacts showed that an increase in the volume fraction of fine powder particles reduced the porosity, permeability level and pore size, and increased the tensile properties. The relationship between permeability and porosity level was non-linear and this was caused by the differences in pore diameters in the compacts. The capillary tube model was used to discuss the relationship between the permeability, pore diameter and porosity. Using this information, a graded porosity compact was designed and fabricated by slip casting. A future study on this graded porosity compacts is recommended to undertake in more depth.

text: Synthesis, Microstructure and Mechanical Properties of Titanium with Controlled Levels of Porosity Porous titanium (Ti) products have many applications due to their excellent corrosion resistance, high strength-to-weight ratio, high specific surface area, etc. However, the major limitation is the expensive cost of porous Ti products because of the high raw materials costs and the difficulty of processing. The novelty of this research work is concerned with a study of a ceramic casting technique, slip casting, to create porous Ti products and the effect of porosity on the mechanical properties and gas permeability of Ti compacts. 

An optimised Ti slurry was developed from 43 vol.% of Ti powder, 0.3 dw.% of dispersant, 0.8 dw.% of plasticiser and 0.8 dw.% of binder, mixed with a balance of distilled water, which produced a viscosity of 290 cP. It was then poured into a plaster mould to form compacts with a green density of 45%. Thermal debinding was carried out at 320°C with an argon flow for 2 hours, followed by vacuum sintering different samples at 1000°C and 1200°C for 0.5 hours, respectively. The porous sintered compacts had satisfactory tensile strength with some plastic deformation. The increase in oxygen and carbon content during processing was minor. The results from this investigation suggested that slip casting is a potentially low-cost, simple manufacturing route for porous Ti products.

Porous Ti compacts with porosity in the range of 12.3 vol.% to 35.3 vol.% were fabricated by slip casting. The mechanical properties, fracture morphology, gas permeability, pore size analysis and pore shape factors for the porous Ti compacts were determined for different porosity levels. A decreasing porosity level resulted in less open porosity and gas permeability, reduced pore size, and an increased tensile stress and elongation. The mechanical properties of porous Ti compacts produced by slip casting were comparable with more conventional press and sintered materials at the same porosity levels. Theoretical models for tensile stress and ductility as a function of porosity were examined and incorporated into the results and differences between the theoretical models and experimental results are discussed. The pore shape factor analysis showed that tensile loading would stretch the pores in the compacts to produce more irregular pores, which were acting as linkage sites to allow the propagation of cracks. Additionally, a novel interconnected pore characterisation method using ammonium meta-tungstate solution is presented. By using backscatter scanning electron microscopy, the interconnected pores can be directly observed. 

The packing behaviour and sintering behaviour of Ti compacts fabricated with different particles size distribution were characterised and studied, in terms of porosity, pore size analysis, tensile properties and gas permeability. Two different particles size (avg. 14 μm & avg. 56 μm) of pure Ti hydride-dehydride powder were used in five volume proportions (20:80, 40:60, 60:40, 80:20 & 100:0). A theoretical model predicted that the green density reaches a maximum when the volume fraction of fine particles is 0.35. It was found that although experimental results showed similar behaviour there was no well-defined maximum green density. The sintered compacts showed that an increase in the volume fraction of fine powder particles reduced the porosity, permeability level and pore size, and increased the tensile properties. The relationship between permeability and porosity level was non-linear and this was caused by the differences in pore diameters in the compacts. The capillary tube model was used to discuss the relationship between the permeability, pore diameter and porosity. Using this information, a graded porosity compact was designed and fabricated by slip casting. A future study on this graded porosity compacts is recommended to undertake in more depth.

year: 2014

title: Tino rangatiratanga in health policies and practises

authors: Wihongi, Helen Annette

subjects: tino rangatiratanga

abstract: The purpose of my doctoral research was to investigate tino rangatiratanga in health policies and practises in Aotearoa. My research involved defining tino rangatiratanga and exploring the expression of tino rangatiratanga in health policy and practises. A kaupapa Māori analysis of the 1996 National Cervical Screening Programme’s Policy document was at the core of the policy investigation. The analysis involved developing a kaupapa Māori analysing framework and then analysing the 1996 National Cervical Screening Policy document for empirical and normative judgements at four discursive levels, health gains, health objectives, health goals and fundamental underlying values. A Kaupapa Māori research design drew on interdisciplinary scholarship on colonisation, Te Tiriti o Waitangi, community psychology, public policy, disability theory, feminist theory and discourse theory.

I argue that the dominance of Western cultural norms and state-directed policies were made possible by the signing of Te Tiriti o Waitangi. The signing of Te Tiriti saw Crown sovereignty being implemented and tino rangatiratanga ignored. The consequences for Māori have been disastrous with loss of land and economic base which has resulted in poor health status. I also argue that tino rangatiratanga has the potential to transform the social and political context that frame Aotearoa society. Such an approach raises a critical dilemma for the state as meaningful recognition of tino rangatiratanga requires waiving full and absolute sovereignty which currently resides in the state. Hence some scholars argue that tino rangatiratanga is a site for constructive engagement where state and Māori relationships can be renegotiated. The extent to which this potential for constructive engagement is being realised in however is inadequately explored in the scholarly literature. Exploring the relationships between tino rangatiratanga and health policies and practises as undertaken in my thesis will therefore contribute to scholarly knowledge on the subject.

The findings from the research show that tino rangatiratanga is indeed a complex, fluid, multi-faceted and context related concept. Within the context of my research, tino rangatiratanga is defined as Māori sovereignty, self determination, and positive Māori development. As a Māori value it is about mana and tapu of rangatira or leadership personified. Within policies, tino rangatiratanga has emerged through resistance and demonstration and is actualised through Tiriti legislation and policies.

The legitimation of tino rangatiratanga in cervical screening services sees Māori leadership at national, regional and local levels and Māori involvement through wide ranging consultation but the Crown still controls the policy process and therefore the outcomes. Most cervical screening services are still owned and operated by the Crown or Crown agencies.

One of the consequences of Crown control is that Māori women are still twice as likely to get cervical cancer and four times more likely to die from it. To some degree this may be the result of resource allocation and the result of discriminatory service practices but also the result of resistance to the procedure itself.

Tino rangatiratanga within cervical screening services could be strengthened through iwi ownership of some cervical screening register sites. At the time of my field work (2000) there were 14 sites, all owned and operated by Crown agents. Tino rangatiratanga could also be strengthened through funding criteria that ensure practitioners are safe to practise, through the adoption of less invasive procedures and through the legitimation of Māori healing practises such as rongoā and karakia.

Overall if tino rangatiratanga is to be given full effect within the policy domain Māori must have a well established asset base, they must be in control of the decision making making process including resource allocation, service delivery must address the diversities of Māori realities and Māori must be the recipients of policy decisions made.

text: Tino rangatiratanga in health policies and practises The purpose of my doctoral research was to investigate tino rangatiratanga in health policies and practises in Aotearoa. My research involved defining tino rangatiratanga and exploring the expression of tino rangatiratanga in health policy and practises. A kaupapa Māori analysis of the 1996 National Cervical Screening Programme’s Policy document was at the core of the policy investigation. The analysis involved developing a kaupapa Māori analysing framework and then analysing the 1996 National Cervical Screening Policy document for empirical and normative judgements at four discursive levels, health gains, health objectives, health goals and fundamental underlying values. A Kaupapa Māori research design drew on interdisciplinary scholarship on colonisation, Te Tiriti o Waitangi, community psychology, public policy, disability theory, feminist theory and discourse theory.

I argue that the dominance of Western cultural norms and state-directed policies were made possible by the signing of Te Tiriti o Waitangi. The signing of Te Tiriti saw Crown sovereignty being implemented and tino rangatiratanga ignored. The consequences for Māori have been disastrous with loss of land and economic base which has resulted in poor health status. I also argue that tino rangatiratanga has the potential to transform the social and political context that frame Aotearoa society. Such an approach raises a critical dilemma for the state as meaningful recognition of tino rangatiratanga requires waiving full and absolute sovereignty which currently resides in the state. Hence some scholars argue that tino rangatiratanga is a site for constructive engagement where state and Māori relationships can be renegotiated. The extent to which this potential for constructive engagement is being realised in however is inadequately explored in the scholarly literature. Exploring the relationships between tino rangatiratanga and health policies and practises as undertaken in my thesis will therefore contribute to scholarly knowledge on the subject.

The findings from the research show that tino rangatiratanga is indeed a complex, fluid, multi-faceted and context related concept. Within the context of my research, tino rangatiratanga is defined as Māori sovereignty, self determination, and positive Māori development. As a Māori value it is about mana and tapu of rangatira or leadership personified. Within policies, tino rangatiratanga has emerged through resistance and demonstration and is actualised through Tiriti legislation and policies.

The legitimation of tino rangatiratanga in cervical screening services sees Māori leadership at national, regional and local levels and Māori involvement through wide ranging consultation but the Crown still controls the policy process and therefore the outcomes. Most cervical screening services are still owned and operated by the Crown or Crown agencies.

One of the consequences of Crown control is that Māori women are still twice as likely to get cervical cancer and four times more likely to die from it. To some degree this may be the result of resource allocation and the result of discriminatory service practices but also the result of resistance to the procedure itself.

Tino rangatiratanga within cervical screening services could be strengthened through iwi ownership of some cervical screening register sites. At the time of my field work (2000) there were 14 sites, all owned and operated by Crown agents. Tino rangatiratanga could also be strengthened through funding criteria that ensure practitioners are safe to practise, through the adoption of less invasive procedures and through the legitimation of Māori healing practises such as rongoā and karakia.

Overall if tino rangatiratanga is to be given full effect within the policy domain Māori must have a well established asset base, they must be in control of the decision making making process including resource allocation, service delivery must address the diversities of Māori realities and Māori must be the recipients of policy decisions made.

year: 2010