title: Alternative sulfur acquisition pathways in Neisseria gonorrhoeae

authors: van Niekerk, Stacy Lyn

subjects: Microbiology

abstract: Neisseria gonorrhoeae is an obligate human pathogen responsible for the sexually transmitted infection, gonorrhoea. Its success as a pathogen is partly due to robust defence mechanisms that provide protection against oxidative stress encountered during infection. Reduced sulfur compounds such as glutathione, cysteine and methionine are integral to this response and pathogenic growth.

Due to a large genomic deletion and pseudogenes, N. gonorrhoeae is incapable of sulfur acquisition via traditional routes and therefore cannot grow when sulfate is the sole sulfur source. However, N. gonorrhoeae can grow in the presence of thiosulfate but lacks the ability to reduce thiosulfate via the conventional thiosulfate reduction pathway. This raises questions of how N. gonorrhoeae acquires sulfur for cysteine biosynthesis?

We have identified two sulfurtransferase enzymes (Str and PspE) in N. gonorrhoeae that we hypothesise provide sulfur in the form needed for cysteine synthesis. We show these enzymes have thiosulfate-thiol sulfurtransferase activity and, importantly, produce sulfide that could be utilised for cysteine biosynthesis. Furthermore, we demonstrate that Str is a promiscuous enzyme with respect to thiol acceptor substrates and, intriguingly, is capable of cyanide detoxification. Our N. gonorrhoeae sulfurtransferase deletion strain has a reduced ability to grow when thiosulfate is the only available sulfur source, supporting our hypothesis that Str utilises exogenous inorganic thiosulfate. However, due to functional redundancy provided by the presence of the second sulfurtransferase, PspE, construction of a double knockout strain is essential in understanding the full effect of these enzymes in relation to pathogenicity.

Our proposed energetically favourable pathway of thiosulfate reduction via sulfurtransferase enzymes could be pivotal in advancing our understanding of how pathogens fulfil their sulfur requirements. However, much is to be elucidated regarding the role of these ubiquitous enzymes in bacterial pathogens. Herein, this thesis offers insight into the versatility, function, and formal mechanisms of sulfurtransferases within N. gonorrhoeae.

text: Alternative sulfur acquisition pathways in Neisseria gonorrhoeae Neisseria gonorrhoeae is an obligate human pathogen responsible for the sexually transmitted infection, gonorrhoea. Its success as a pathogen is partly due to robust defence mechanisms that provide protection against oxidative stress encountered during infection. Reduced sulfur compounds such as glutathione, cysteine and methionine are integral to this response and pathogenic growth.

Due to a large genomic deletion and pseudogenes, N. gonorrhoeae is incapable of sulfur acquisition via traditional routes and therefore cannot grow when sulfate is the sole sulfur source. However, N. gonorrhoeae can grow in the presence of thiosulfate but lacks the ability to reduce thiosulfate via the conventional thiosulfate reduction pathway. This raises questions of how N. gonorrhoeae acquires sulfur for cysteine biosynthesis?

We have identified two sulfurtransferase enzymes (Str and PspE) in N. gonorrhoeae that we hypothesise provide sulfur in the form needed for cysteine synthesis. We show these enzymes have thiosulfate-thiol sulfurtransferase activity and, importantly, produce sulfide that could be utilised for cysteine biosynthesis. Furthermore, we demonstrate that Str is a promiscuous enzyme with respect to thiol acceptor substrates and, intriguingly, is capable of cyanide detoxification. Our N. gonorrhoeae sulfurtransferase deletion strain has a reduced ability to grow when thiosulfate is the only available sulfur source, supporting our hypothesis that Str utilises exogenous inorganic thiosulfate. However, due to functional redundancy provided by the presence of the second sulfurtransferase, PspE, construction of a double knockout strain is essential in understanding the full effect of these enzymes in relation to pathogenicity.

Our proposed energetically favourable pathway of thiosulfate reduction via sulfurtransferase enzymes could be pivotal in advancing our understanding of how pathogens fulfil their sulfur requirements. However, much is to be elucidated regarding the role of these ubiquitous enzymes in bacterial pathogens. Herein, this thesis offers insight into the versatility, function, and formal mechanisms of sulfurtransferases within N. gonorrhoeae.

year: 2021

title: Soil and permafrost distribution, soil characterisation and soil vulnerability to human foot trampling, Wright Valley, Antarctica

authors: McLeod, Malcolm

abstract: Soils and shallow permafrost in Wright Valley, Antarctica were mapped at a scale of 1:50 000 to depict their spatial distribution, and sampled to determine the main drivers for the soil classification. 

In the cold desert of Wright Valley the Gelisol order of Soil Taxonomy was used to classify the soils. Soils on younger surfaces, associated with Lower Wright Glacier, Upper Wright Glacier and alpine glaciers, contain massive ice within 100 cm of the soil surface and are classified as Glacic Haplorthels or Glacic Haploturbels where there is field evidence of cryoturbation. As a generalization, at either end of the valley, soil moisture recharge from moist coastal air masses (eastern end) and blowing snow drifts maintain the depth to permafrost in which ice-cement occurs at <70 cm. The resulting shallow effective soil depth restricts soil development. Soils associated with the Onyx River and those receiving overland or subsurface flow also have a shallow depth to ice-cemented permafrost. Where there is permafrost in which the depth to ice-cement is <70 cm the soils are classified as Typic Haplorthels, or Haploturbels where there is field evidence of cryoturbation. Field evidence of cryoturbation includes patterned ground, sand wedges, or post-depositional distorted layering within the soil. Soils near central Wright Valley often show more development compared with those at the eastern or western ends of the valley and, where permafrost without ice-cement extends to >70 cm, are classified as Salic or Typic Anhyorthels or, where there is field evidence of cryoturbation, Anhyturbels.

While mapping soils in Wright Valley, the distribution and nature of the shallow permafrost were also investigated. Three classes of permafrost were established to coincide with definitions or conditions within Soil Taxonomy viz: permafrost with ice-cement at <70 cm, dry permafrost to a depth of >70 cm, and massive ice. 

A definition for a petrosalic horizon is proposed based on the properties of a salic horizon and the indurated nature of petrocalcic/petrogypsic horizons. The horizon is likely to occur only in the cold desert climate zones of Antarctica.

A rapid method to determine soil vulnerability to human foot traffic was developed. As vulnerability is the product of disturbance and rehabilitation, the method is based on the disturbance of 10 foot prints at a site multiplied by a soil rehabilitation factor based on the soil weathering stage. Although fine-grained aeolian sands are easily disturbed they also rehabilitate rapidly in the windy conditions of Wright Valley. In contrast, old stable soils have a tight cobbly desert pavement with reddish desert varnish and often show less foot print disturbance. When cobbles are overturned, however, fresh rock with thick salt accumulations and without desert varnish is exposed. It takes much time for the desert varnish to re-establish.

The spatial distribution of Soil Taxonomy soil classes, nature of the permafrost and soil vulnerability to human traffic are presented as three separate maps at 1:50 000 scale and as live GIS files.

text: Soil and permafrost distribution, soil characterisation and soil vulnerability to human foot trampling, Wright Valley, Antarctica Soils and shallow permafrost in Wright Valley, Antarctica were mapped at a scale of 1:50 000 to depict their spatial distribution, and sampled to determine the main drivers for the soil classification. 

In the cold desert of Wright Valley the Gelisol order of Soil Taxonomy was used to classify the soils. Soils on younger surfaces, associated with Lower Wright Glacier, Upper Wright Glacier and alpine glaciers, contain massive ice within 100 cm of the soil surface and are classified as Glacic Haplorthels or Glacic Haploturbels where there is field evidence of cryoturbation. As a generalization, at either end of the valley, soil moisture recharge from moist coastal air masses (eastern end) and blowing snow drifts maintain the depth to permafrost in which ice-cement occurs at <70 cm. The resulting shallow effective soil depth restricts soil development. Soils associated with the Onyx River and those receiving overland or subsurface flow also have a shallow depth to ice-cemented permafrost. Where there is permafrost in which the depth to ice-cement is <70 cm the soils are classified as Typic Haplorthels, or Haploturbels where there is field evidence of cryoturbation. Field evidence of cryoturbation includes patterned ground, sand wedges, or post-depositional distorted layering within the soil. Soils near central Wright Valley often show more development compared with those at the eastern or western ends of the valley and, where permafrost without ice-cement extends to >70 cm, are classified as Salic or Typic Anhyorthels or, where there is field evidence of cryoturbation, Anhyturbels.

While mapping soils in Wright Valley, the distribution and nature of the shallow permafrost were also investigated. Three classes of permafrost were established to coincide with definitions or conditions within Soil Taxonomy viz: permafrost with ice-cement at <70 cm, dry permafrost to a depth of >70 cm, and massive ice. 

A definition for a petrosalic horizon is proposed based on the properties of a salic horizon and the indurated nature of petrocalcic/petrogypsic horizons. The horizon is likely to occur only in the cold desert climate zones of Antarctica.

A rapid method to determine soil vulnerability to human foot traffic was developed. As vulnerability is the product of disturbance and rehabilitation, the method is based on the disturbance of 10 foot prints at a site multiplied by a soil rehabilitation factor based on the soil weathering stage. Although fine-grained aeolian sands are easily disturbed they also rehabilitate rapidly in the windy conditions of Wright Valley. In contrast, old stable soils have a tight cobbly desert pavement with reddish desert varnish and often show less foot print disturbance. When cobbles are overturned, however, fresh rock with thick salt accumulations and without desert varnish is exposed. It takes much time for the desert varnish to re-establish.

The spatial distribution of Soil Taxonomy soil classes, nature of the permafrost and soil vulnerability to human traffic are presented as three separate maps at 1:50 000 scale and as live GIS files.

year: 2012

title: The waters of the Maori: Maori law and state law

authors: Durie, Edward Taihākurei

abstract: This paper is for filing in the Waitangi Tribunal in relation to a claim that existing laws do not adequately accommodate the Māori proprietary interest in natural, water resources. The claim was initiated by the New Zealand Māori Council in association with ten tribal groups. It was later accompanied by 166 other Māori groups, whom the Tribunal joined as interested parties.

text: The waters of the Maori: Maori law and state law This paper is for filing in the Waitangi Tribunal in relation to a claim that existing laws do not adequately accommodate the Māori proprietary interest in natural, water resources. The claim was initiated by the New Zealand Māori Council in association with ten tribal groups. It was later accompanied by 166 other Māori groups, whom the Tribunal joined as interested parties.

year: 2017