Browsing by Author "Postma, Anneke"

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    Gedeeltelike beskrywing van bakteriee in die SVK van Haliotis midae, met die fokus op potensiele probiotika
    (LitNet, 2015-08) Postma, Anneke; Jacobs, Karin
    Perlemoenboerdery is een van Suid-Afrika se belangrikste akwakultuurbedrywe. Van die grootste probleme in hierdie bedryf is die stadige groeitempo van die perlemoen en ekonomiese verliese as gevolg van siektes. Daar word derhalwe swaar gesteun op die gebruik van antibiotika vir die beheer en behandeling van bakteriële infeksies in akwakultuurspesies. As gevolg van die ontwikkeling van antibiotikaweerstandigheid in bakterieë en die betreklik maklike verspreiding daarvan in akwatiese omgewings, word die gebruik van antibiotika bevraagteken. ’n Alternatief vir die gebruik van antibiotika is probiotika, ’n lewende mikrobiese aanvulling wat ’n positiewe effek op die gasheer het, en wat die mikrobiese gemeenskappe wat met die gasheer en die onmiddellike omgewing geassosieer word, verander. Die doel van hierdie studie was die isolering en identifisering van bakterieë in die spysverteringsverteringskanaal (SVK) van Suid-Afrikaanse perlemoen, Haliotis midae. Die isolate is oorweeg as ’n potensiële probiotikum gebaseer op bestaande literatuur.
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    Soil microbial communities associated with two commercially important plant species indigenous to the fynbos region of South Africa : cyclopia spp. (honeybush) and Aspalathus linearis (rooibos)
    (Stellenbosch : Stellenbosch University, 2016-12) Postma, Anneke; Jacobs, Karin; Slabbert, Etienne; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: The Cape Floristic Region (CFR) is characterized by nutrient poor soils which forged close symbiotic ties between plants and soil microorganisms for nutrient acquisition. Aspalathus linearis and Cyclopia spp. are two commercially important plant species endemic to the CFR in South Africa. These species are used to produce herbal teas known as rooibos and honeybush tea, respectively. Despite the important role soil microorganisms play in this environment, very few studies have been done to investigate the diversity and structure of the communities associated with these economically important plants. Furthermore, it is unclear what the effect of agricultural practices will be on these communities. Studies done on other agricultural systems, showed that the soil microbiome is greatly influenced by agricultural activities such as soil tillage, application of pesticides as well as monocropping systems. These activities often lead to the loss of soil productivity and biodiversity. We, therefore, hypothesised that the microbial communities associated with A. linearis and Cyclopia spp. plants will also be influenced by the respective agricultural activities. The overall aim of this study was to characterise and compare microbial communities associated with natural and commercially grown A. linearis and Cyclopia spp. plants. Furthermore, we aimed to investigated the effect different abiotic and physico-chemical factors may have on microbial communities in this unique region. Sampling was done on two occasions to include the dry, warm summer and the cold, wet winter seasons. A total of 29 bulk soil and 54 rhizosphere soil samples were collected during this study. The abiotic and physico-chemical properties of the soil samples were determined which included soil resistance, pH, total soil carbon, Na+, K+, nitrate and ammonia. Bacterial and fungal communities were characterised using next generation sequencing technology on the Ion Torrent (PGM) platform. For the bacteria, variable V4-V5 region of the 16S rRNA gene were amplified and sequenced. Fungal analysis used the internal transcribed spacer (ITS) region of the 18S rRNA gene. Bioinformatic and statistical analyses were performed using the software packages MOTHUR, PIPITS and R. No statistically significant differences were detected between bacterial communities from natural and commercial sites for both A. linearis and Cyclopia spp. plants. The plant-driven selection of rhizosphere microbiome for these two fynbos plants appeared to be very strong and was not significantly influenced by agricultural activities. However, significant differences in bacterial communities were observed between samples collected during the different seasons. These seasonal changes support the contention that microbial taxa adapt and resist environmental changes differently. Furthermore, the overall taxonomic classification indicated that all soils were dominated by the bacterial orders Acidobacteriales and Actinomycetales. Both these groups are known to be dominant soil colonizing bacteria and are able to grow under low nutrient conditions, characteristic to the fynbos region. Additionally, the most dominant fungal phyla detected in samples included the Ascomycota and Basidiomycota. Cyclopia spp. samples were mostly dominated by the orders Agaricales, Chaetothyriales and Mortierellales, whereas A. linearis samples were dominated by the orders Chaetothyriales, Eurotiales and Helotiales. The β-diversity analysis showed that the Cyclopia spp. samples tended to cluster into commercial and natural groups. This might be due to the differences measured in soil pH between these two groups. Overall, little evidence was found to support our hypothesis. Bacterial communities from natural and commercial soil of both plant species were very similar and fungal communities associated with natural and commercially grown A. linearis plants also did not reveal any significant difference. However, fungal communities associated with natural and commercially grown Cyclopia spp. plants appeared to differ. In short, this study improved our knowledge on the biodiversity of soil microorganisms associated with two commercially important fynbos plant species and elucidated on factors that affected the microbial community structures.