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Active layer dynamics at four borehole sites in western dronning maud land, antarctica
No full textPermafrost and active layer dynamics in the Antarctic play an important role within terrestrial landscapes and ecosystems and as a climate change indicator. However, they remain less thoroughly researched than their Northern-Hemispheric counterpart. Despite advancements made by ANTPAS on the permafrost and active layer monitoring network in the Antarctic, observational gaps still exist. Western Dronning Maud Land (WDML) has been identified as one of these gaps, necessitating further research on permafrost dynamics and the influence of climate parameters thereon. Such elucidation is critical to both the cryospheric and life sciences. Variations in the surface climate of Antarctica can be seen as a result of inter-annual variations in atmospheric circulation, enhancing permafrost degradation and active layer thickening which directly affects soil processes, such as sorting and cryoturbation. Ground temperatures from four permafrost boreholes from WDML were analysed from 2007 to 2014. The study sites exhibit seasonal freezing, periglacial landforms, and altitudinal variation, ranging between ca. 450masl to ca. 1300masl. Using ground thermal regime and regional climate data, the spatial and temporal variability of the active layer in the Ahlmannryggen and Jutulsessen areas of WDML were characterised. 137 Cs tracing has revealed that the active layer and associated landforms have been active over the past half century. Further results show that active layer depths at each site vary inter-annually and are particularly influenced by snow cover, altitude and distance to the ice-shelf. Moreover, a correlation between the SAO (Semi-Annual Oscillation) and measured ground temperatures was found, principally during the transitional season of the SAO in May and September. The relationship between climate and ground thermal regimes, especially the influence of teleconnections thereon, is essential to improving the understanding of permafrost dynamics and landform morphology in continental Antarctica.National Research Foundatio
Optimised bacterial production and characterisation of natural antimicrobial peptides with potential application in agriculture
No full textThe use of chemical control agents to control microbial spoilage in agriculture has been compromised
with the emergence of increasing microbial resistance, together with a shift in regulation toward
pesticides with a lower intrinsic toxicity and lower environmental impact. This has instigated the
search for alternate so-called green-biocides with a reduced environmental impact together with
alternate modes of action to conventional chemical control agents to combat the trend of resistance
development.
The antimicrobial peptides of focus in study may offer a potential solution. The tyrocidines and their
analogues (Trcs) are a group of cyclodecapeptides [cyclo(D-Phe1
-L-Pro2
-L-(Phe3
/Trp3
)-D-
(Phe4
/Trp4
)-L-Asn5
-L-Gln6
-L-(Tyr7
/Phe
7
/Trp7
)-L-Val8
-L-Orn9
-L-Leu10] produced by the soil
bacterium Bacillus aneurinolyticus. These cyclodecapeptides have shown potent antimicrobial
activity toward a broad range of pathogens which affect the agricultural industries including Grampositive
bacteria as well as fungi. In addition to a rapid membrane lytic activity, they have alternate
cellular targets that reduces the likelihood of resistance development. Increased antimicrobial activity
toward different targets is achieved by different analogues which contain a variable primary structure
mainly due to variation in aromatic amino acid content at residues 3, 4 and 7 in the
cyclodecapeptides.
The first objective of this study was to elucidate the optimal conditions that would allow for the large
scale production of target-specific subsets of these cyclodecapeptides that would enable their
utilisation as green-biocides in the agricultural industry. Supplementation of defined ratios of Phe/Trp
in the growth media shifted the cyclodecapeptide production profile to defined subsets of different
analogues, as defined by changes in aromatic amino acids in their primary structures. Increased
natural cyclodecapeptide production was achieved in excess of one gram per litre in flask cultures.
Purification of culture extracts, either by manipulation of solubility of the cyclodecapeptides in
solution or via column chromatography, achieved a peptide complex purity of >75% to utilise in
agricultural applications. Further purification via high performance liquid chromatography yielded
single peptides with purity >90%. The production and purification methodologies are of such a nature
as to allow for future upscaling.
Investigation of the relationship between the structure and oligomerisation of the six major
cyclodecapeptides produced in the different subsets under various Phe/Trp supplemented conditions
revealed a relationship between increased hydrophobicity and the tendency to form dimeric
structures, the proposed membrane active units. Increased higher order structure formation, however,
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iv
was dependent on intermediate hydrophobicity and dimerization. This coincided with structures of
the tyrocidine A (Phe3
, Phe4
and Tyr7
) and tyrocidine B (Trp3
, Phe4
and Tyr7
) analogues.
Furthermore, glucose disrupted higher order structures of analogues containing Phe4
together with
Tyr7 or Phe7
. These properties correlated with increased antifungal activity toward Aspergillus
fumigatus. Antifungal activity was found to be related to a balance in hydrophobicity and higher
structure formation where interaction with hexose moieties in the target cell wall may play a role in
the mode of action and possible pore formation in the target membrane. In contrast antibacterial
activity toward Bacillus subtilis was found to be independent of dimerization and the variable
characteristics of the different cyclodecapeptide analogues. Antibacterial activity was possibly more
dependent on the conserved pentapeptide (VOLfP), as near equivalent activity was observed by 5 of
the 6 analogues. Co-produced cyclodecapeptide pairs showed a propensity of forming heterodimers
that mostly lead to additive antimicrobial activity. However, overt antagonism was observed in
peptide combinations containing tryptocidines (Trp7
) which are not naturally produced in increased
quantities, while synergism was observed in for the naturally produced combinations of TrcA:PhcA
(Phe3
; Phe4
) and TrcA:TrcB (Phe3
; Phe4
, Tyr7 and Trp3
; Phe4
, Tyr7
) toward the fungal target, and
TrcA:TrcB and TrcB:TrcC (Phe3
; Trp4
, Tyr7 and Trp3
; Trp4
, Tyr7
) toward the bacterial target.
Characteristics of intermediate hydrophobicity and dimerization in peptide pairs again resulted in
increased activity toward the fungal target. These peptide mixtures, specifically TrcA and TrcB, are
naturally produced in high quantities, indicating an evolutionary advantage to the producer strain.
Formulation of the cyclodecapeptide mixtures in ethanol or dimethylformamide (DMF) revealed
changes in oligomerisation, with reduced dimerization in ethanol relative to DMF. Furthermore,
glucose and sucrose were observed to suppress antimicrobial activity when dissolved in ethanol,
however, this was largely relieved when dissolved in DMF. The interaction of the cyclodecapeptides
with sugar like moieties depended on a balance between the active conformation and target cell
properties. Formulations of the natural peptide extract (Te) in 50% sucrose and DMF were found to
be non-toxic towards toward adult bees and in field trials the Te-treated bees showed increased
survival.
These cyclodecapeptides offer an alternate solution to conventional chemical agents to treat
pathogens in the agricultural and food industries. Optimized formulation of these cyclodecapeptides
would possibly enhance their potential. In order to harvest the potential of these cyclodecapeptides, a
concerted effort must be made in future investigations to gain knowledge on their mode of action,
toxicity and behaviour as mixtures.National Research Foundatio
Bulk geochemical, biomarker and leaf wax isotope records of mfabeni peatland, KwaZulu-Natal, South Africa since the late pleistocene
No full textSouthern Africa is a topographically diverse region that is influenced by temperate, sub-tropical
and tropical climates encompassing varying rainfall zones. The core regional contemporary
climatic drivers are the large sea surface temperature (SST) gradients between the Atlantic and
Indian Oceans, and seasonal fluctuations in the Inter Tropical Convergence Zone (ITCZ). Our
understanding of how these two mechanisms interacted in the past and how ecosystems
responded to these climate drivers is ambiguous, mainly due to a lack of continuous archives as a
consequence of the region‘s semi-arid climate. The Mfabeni peatland is a 11 m thick continuous
peat sequence that has been dated to ca. 47 kcal yr BP. It is the only known coastal peatland
record in the summer rainfall zone of Southern Africa to transcend the Last Glacial Maximum
(LGM), and gives us the opportunity to reconstruct high-resolution palaeoenvironment records
under both glacial and interglacial conditions on the south eastern coastline of the African
continent.
A diverse set of geochemical techniques and analysis (bulk C and N elemental and stable
isotopes; different biomarkers and leaf wax δ
13C isotope) was undertaken on a 810 cm long core to
reconstruct primary productivity, organic matter (OM) sources, rates of OM remineralisation,
peatland hydrology and relative contributions of C3 and C4 plant matter into the peat deposit.
These geochemical climatic indicators were used to infer precipitation intensities and relative
temperatures at time of sedimentation and, in conjunction with other regional archives, the
dominant mechanisms (Indian Ocean SST changes versus changes in the position of ITCZ) driving
climatic fluctuations since the late Pleistocene were explored.
We established the Mfabeni peatland to be a well-preserved and unique palaeoecological archive
that recorded both environmental and climatic signals throughout the depositional history of the
peatland. Even though the dominant OM source of the peat was terrestrial and emergent plants,
there were definitive periods of predominant submerged macrophyte input, suggesting elevated
water levels. A general positive trend was observed between the temperature and moisture
proxies, however the local plant physiology (n-alkane chain lengths; ACLalk) and plant types
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(terrestrial vs aquatic and their influence on OM lability; CPIalk) was dominated by moisture
availability as opposed to temperature variations, arguably due to the relatively moderate cooling
experience in the sub-tropics during the LGM. The leaf wax C isotope data set established
variability in the proportional balance of C3 and C4 plants, with interchanges between plant clades
and inter family C3 and C4 switches in response to changes in environmental conditions.
However, plant assemblage shifts were absent during some of the more ephemeral climatic events
which we concluded was due to local hydrological overprinting.
The Mfabeni archive correlates strongly with Mozambique Channel SST records, suggesting the
dominant climate forcing factor in south eastern Africa to be the evaporation potential and
advection of moisture from the adjacent Indian Ocean since the late Pleistocene. It was also noted
that the Mfabeni record exhibited overall opposite environmental responses to Northern
Hemisphere climatic events, suggesting an anti-phase coupling between the two hemispheres.National Research Foundatio
Design of stormwater ponds towards the reduction of metal toxins in surface waters that are utilised for South African primary food production
No full textThis research originated from a need for civil engineering practice to address metal pollution in stormwater runoff. Specific emphasis was placed on metals that could affect the quality of crops, livestock and fish in South Africa.
Detention and retention ponds are commonly used for surface water quality control, and these types of structures were therefore investigated. No prominent pond design methods were found, however, that directly incorporate consideration of metal pollution in the context of food security. In addition, there was a lack of information on how methods could be adapted to address metal pollution specifically. It was argued that focussing on relationships between pond efficiency and design could generate information towards augmenting design philosophies and methodologies. This became the project thesis.
The methodology used for the investigation into relationships between pond efficiency and design was constrained by the available data. Statistics and probability theory were the main tools used. Data was obtained from an international database and therefore little was known about possible sources of error. Although a large variety of data on a number of metal toxins and solids was found, individual data sets were often small. These factors meant that data trends (rather than specifics) between ponds were used as the basis for conclusions. Modelling was employed to theoretically test the validity of trends indicated by statistical analysis. These included identification of pond efficiency predictors with logistic regression, curve fitting of a time polynomial to outflow mass data to indicate the class of particulate settling, and hypothetical sedimentation modelling with MIKE 11 software.
Results indicated certain pond parameters that were influential in removal processes, but many of these were not explicitly included in prominent design methods. These methods were therefore found to be inadequate for efficient pond design. Data trends indicated a number of processes of importance in metals removals. This information was used to create conceptual models of pond functioning, which were used to augment established engineering theory for application in pond metals removal. The project thesis was therefore accepted.
A design philosophy of high levels of control on pond hydraulics and metal loads was recommended. Detention and retention pond functioning for metals removal was illustrated to be highly complex, making detailed modelling enterprises difficult, time consuming and costly. Control over hydraulics and in/out boundaries can simplify pond design.National Research Foundatio
Investigation and characterization of the HERA dish and feed using electromagnetic simulations
No full textThis thesis presents the results of the electromagnetic analysis of the dish
and feed for the Hydrogen Epoch of Reionization Array (HERA) experiment.
The science goal for HERA is a challenging task in the form of detecting and
characterizing the power spectrum of the Epoch of Reionization (EoR).
The HERA faceted parabolic dish is investigated where it is determined
that, at the relevant frequencies, the panels forming the dish is not a significant
deviation from a perfect paraboloid. However, the screen placed on
the dish does cause variations in the gain across frequency. The mutual coupling
between several HERA elements is determined not to be significant even
without including the screen. Furthermore, at 150 MHz it is found that the
HERA dish delivers a Field of View of approximately 9 and sidelobe levels
of 15 dB below the main beam, which has a gain of 25 dB. The beam level
at the horizon is measured at approximately 40 dB below the main beam.
The uv-coverage of HERA as an interferometer is calculated for a tight-packed
hexagon configuration. With the inclusion of outlier elements, this coverage
improves significantly and it is shown that HERA will have excellent imaging
capabilities. The delay-spectrum technique used by HERA astronomers is unpacked
and applied to the HERA dish using electromagnetic simulations and
post-processing. It is determined that reflections off the dish does not meet
the 60 dB power after 60 ns specification. Rather, these reflections are measured
at 35 dB. Results from modelling and optimization in the frequency
domain of alternative feeds for HERA is compared to the current PAPER feed.
This includes several versions of the bowtie feed, a scaled PAPER feed and a
sinuous feed, which is also manufactured and measured. It is shown that such an effort in conjunction with a reflector is met with challenges due to the low
frequency band.National Research Foundatio
Efficient use of resources to ensure sustainability in golf clubs in gauteng
No full textThe hospitality industry is a broad and varied segment of the service industry, with the golf club industry being a sector within it. Resources or services within golf club operations include food and beverage, housekeeping and facilities; all which have an effect on management’s capabilities of business survival. The golf club member is constantly exposed to varying service levels, which result in perception shifts. Guest satisfaction is all important within the hospitality industry, and even as perceptions change, management should constantly be aware of this shift. The ability to measure service and performance levels assists management to detect warning signs concerning the sustainability of the operation. The purpose of this research is to establish whether there is efficient use of all available resources in the form of facilities, human resources and ICT (Information and Communication Technologies), within the various departments at golf clubs in Gauteng in order to deliver quality service, ensure guest satisfaction and sustainability of the business concern. The research utilised a mixed methods and action research design by using a questionnaire for quantitative data collection, as well as in-depth interviews for qualitative data collection. The first stage of data collection involved questionnaires being distributed to general managers at golf clubs in Gauteng. Following this, semi-structured interviews with purposively selected managers were conducted. The data indicates facilities and services that are available, whilst comparing the total number of employees with revenue earned and the efficiency of the operation. As the experience and backgrounds of the general managers are so varied, the interviews were used to identify areas of focus with regard to sustainability. The research concluded that the age of the club, increased number of facilities and increased number of members together with service quality, contributed to the sustainability of the golf clubs. Management in the clubs indicated that the shift in member perception, changes in global trends and subsequent changes in member needs, should be carefully analysed together with the financial status in order to remain relevant to the current members and to attract new members. Keywords: Hospitality, golf clubs, service quality, resource efficiency, performance measurement, sustainability.National Research Foundatio
CAPRISA newsletter April 2014
No full textIn this issue, the feature article this month highlights the recent series of papers published in the journal AIDS and behaviour on adherence interventions and measurement in the CAPRISA 004 trial
Relationships, collaborations and networks
No full textPresentations SA PhD Project Conference: KwaZulu-Natal Province 17 August 2016
South African PhD project : creating diversity for the future
No full textPresentations SA PhD Project Conference: Western Cape Province 13 September 2016