Browsing by Author "Jacobs, Karin"

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    Characterisation of Metarhizium majus (Hypocreales : Clavicipitaceae) isolated from the Western Cape Province, South Africa
    (Public Library of Science, 2021-03-19) Mathulwe, Letodi L.; Jacobs, Karin; Malan, Antoinette P.; Birkhofer, Klaus; Addison, Matthew F.; Addison, Pia
    Entomopathogenic fungi (EPF) are important soil-dwelling entomopathogens, which can be used as biological control agents against pest insects. EPF are capable of causing lethal epizootics in pest insect populations in agroecosystems. During a survey of the orchard soil at an organic farm, different EPF species were collected and identified to species level, using both morphological and molecular techniques. The EPF were trapped from soil samples taken from an apricot orchard. The traps, which were baited in the laboratory, used susceptible host insects, including the last-instar larvae of Galleria mellonella (wax moth larvae) and Tenebrio molitor (mealworm larvae). The potential pathogenicity of the local Metarhizium majus isolate was tested and verified using susceptible laboratory-reared last-instar T. molitor larvae. The identification of the M. majus isolated from South African soil was verified using both morphological and molecular techniques. The occurrence of M. majus in the South African soil environment had not previously been reported.
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    Distribution patterns of Acidobacteriota in different fynbos soils
    (Public Library of Science, 2021-03-22) Conradie, Tersia Andrea; Jacobs, Karin
    Abstract The Acidobacteriota is ubiquitous and is considered as one of the major bacterial phyla in soils. The current taxonomic classifications of this phylum are divided into 15 class-level subdivisions (SDs), with only 5 of these SDs containing cultured and fully described species. Within the fynbos biome, the Acidobacteriota has been reported as one of the dominant bacterial phyla, with relative abundances ranging between 4–26%. However, none of these studies reported on the specific distribution and diversity of the Acidobacteriota within these soils. Therefore, in this study we aimed to first determine the relative abundance and diversity of the Acidobacteriota in three pristine fynbos nature reserve soils, and secondly, whether differences in the acidobacterial composition can be attributed to environmental factors, such as soil abiotic properties. A total of 27 soil samples were collected at three nature reserves, namely Jonkershoek, Hottentots Holland, and Kogelberg. The variable V4- V5 region of the 16S rRNA gene was sequenced using the Ion Torrent S5 platform. The mean relative abundance of the Acidobacteriota were 9.02% for Jonkershoek, 14.91% for Kogelberg, and most significantly (p<0.05), 18.42% for Hottentots Holland. A total of 33 acidobacterial operational taxonomic units (OTUs) were identified. The dominant subdivisions identified in all samples included SDs 1, 2, and 3. Significant differences were observed in the distribution and composition of these OTUs between nature reserves. The SD1 were negatively correlated to soil pH, hydrogen (H+), potassium (K+) and carbon (C). In contrast, SD2, was positively correlated to soil pH, phosphorus (P), and K+, and unclassified members of SD3 was positively correlated to H+, K, and C. This study is the first to report on the specific acidobacterial distribution in pristine fynbos soils in South Africa.
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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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    High nitrogen rates do not increase canola yield and may affect soil bacterial functioning
    (American Society of Agronomy, 2019) Becker, Frederick; MacLaren, Chloe; Brink, Casper J.; Jacobs, Karin; Le Roux, Marcellous R.; Swanepoel, Pieter Andreas
    Nitrogen fertilization has a fundamental role in agricultural productivity. However, injudicious N applications to crops are common. It is important to ensure the minimum N required for satisfactory crop growth is applied but that excess amounts are avoided due to potential impacts on agroecosystem functioning. Nitrogen at 0, 60, and 150 kg ha-1 was applied as limestone ammonium nitrate to plots arranged in a randomized complete block design, on three farms to determine the impact of rate and temporal distribution of fertilizer on canola (Brassica napus L.) production in South Africa, and the effect of N fertilizer application on the composition and diversity of soil bacterial communities. The amount and distribution of N had only minor effects on canola growth (P < 0.05) and no effects on yield or harvest index. Splitting fertilizer into two or three applications throughout the season resulted in more mineral N available in the soil later in the season. Increasing the N rate from 60 to 150 kg ha-1 had a significant impact on bacterial community composition. The lower rate favored bacteria that are more able to break down N-containing carbon sources. No effects of fertilizer amount or distribution were observed on either N fixation potential (number of nifH gene copies) or bacterial community diversity. Overall, a low rate of N fertilizer split into multiple applications is recommended for canola production, as higher rates do not increase yield and may have a detrimental impact on soil carbon and nitrogen cycling.
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    Microbial communities in the fynbos region of South Africa : what happens during woody alien plant invasions
    (MDPI, 2020) Jacobs, Karin; Conradie, Tersia; Jacobs, Shayne
    The Cape Floristic Region (CFR) is globally known for its plant biodiversity, and its flora is commonly referred to as fynbos. At the same time, this area is under severe pressure from urbanization, agricultural expansion and the threat of invasive alien plants. Acacia, Eucalyptus and Pinus are the common invasive alien plants found across the biome and considerable time, effort and resources are put into the removal of invasive alien plants and the rehabilitation of native vegetation. Several studies have shown that invasion not only affects the composition of plant species, but also has a profound effect on the soil chemistry and microbial populations. Over the last few years, a number of studies have shown that the microbial populations of the CFR are unique to the area, and harbour many endemic species. The extent of the role they play in the invasion process is, however, still unclear. This review aims to provide an insight into the current knowledge on the different microbial populations from this system, and speculate what their role might be during invasion. More importantly, it places a spotlight on the lack of information about this process.
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    Mycotoxin production by three different toxigenic fungi genera on formulated abalone feed and the effect of an aquatic environment on fumonisins
    (Nature Research (part of Springer Nature), 2019-04-14) Greeff-Laubscher, Mariska Riana; Beukes, Ilze; Marais, Gert Johannes; Jacobs, Karin
    Mycotoxins are toxic secondary metabolites produced by various filamentous fungi, of which Fusarium, Aspergillus and Penicillium are the three main genera. Fusarium verticillioides is one of the most dominant toxigenic fungal species, associated with fumonisin contamination in grain-based feeds, such as compound abalone feed. Mycotoxin production is influenced by temperature and available nutrients. In this study the aims were: to determine if abalone feed as growth substrate favours mycotoxin production for toxigenic fungi; to determine the most effective temperature for fumonisin production by F. verticillioides on abalone feed; and to assess the effect of the aquatic environment on fumonisin-contaminated abalone feed. A total of 93 fungal isolates were inoculated onto abalone feed, including species belonging to the genera Fusarium, Aspergillus and Penicillium. Feed inoculated with F. verticillioides were incubated at two different temperatures and fumonisin-contaminated feed was submerged into seawater for 24 h. Results showed that mycotoxins were produced when abalone feed was inoculated with toxigenic fungi, and that F. verticillioides produced higher concentrations of fumonisins at a lower temperature. Submerging fumonisin-contaminated feed in seawater showed that this toxin leached into the seawater, lowering the risk of fumonisins to be consumed by abalone.
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    Optimization of automated ribosomal intergenic spacer analysis for the estimation of microbial diversity in fynbos soil
    (Academy of Science of South Africa -- ASSAF, 2010-08) Slabbert, Etienne; Van Heerden, Carel J.; Jacobs, Karin
    Automated ribosomal intergenic spacer analysis (ARISA) has become a commonly used molecular technique for the study of microbial populations in environmental samples. The reproducibility and accuracy of ARISA, with and without the polymerase chain reaction (PCR) are important aspects that influence the results and effectiveness of these techniques. We used the primer set ITS4/ITS5 for ARISA to assess the fungal community composition of two sites situated in the Sand Fynbos. The primer set proved to deliver reproducible ARISA profiles of the fungal community composition with little variation observed between ARISA-PCRs. Variation that occurred in a sample due to repeated DNA extraction is expected for ecological studies. This reproducibility made ARISA a useful tool for the assessment and comparison of diversity in ecological samples. In this paper, we also offered particular suggestions concerning the binning strategy for the analysis of ARISA profiles.
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    A phylogenetic revision of Penicillium sect. Exilicaulis, including nine new species from fynbos in South Africa
    (International Mycological Association, 2016-06-01) Visagie, Cobus M.; Seifert, Keith A.; Houbraken, Jos; Samson, Robert A.; Jacobs, Karin
    A survey of the fynbos biome in South Africa resulted in the isolation of 61 Penicillium species from Protea repens infructescences, air, and soil samples. Fourteen of these belong to Penicillium sect. Exilicaulis and therefore we considered it an opportunity to re-evaluate the taxonomy of the section. Phylogenetic comparisons of the ITS, β-tubulin, calmodulin and RPB2 gene regions of the 76 section Exilicaulis species, revealed 52 distinct species, including nine new species from fynbos. Morphological comparisons confirmed the novelty for most of these, however, new species closely related to P rubefaciens did not show significant or consistent morphological differences and we thus placed a bias on phylogenetic data applying the Genealogical Concordance Phylogenetic Species Recognition (GCPSR) concept. In this paper we describe the nine new species and update the accepted species list and resolve synonyms in the section. Importantly, we reveal that P. citreosulfuratum is the correct name for the clade previously considered to represent P. toxicarium fide Serra et al. (2008). The nine new species are: Penicillium atrolazulinum, P consobrinum, P cravenianum, P. hemitrachum, P pagulum, P repensicola, P momoii, P subturcoseum, and P xanthomelinii spp. nov.
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    Seasonal and Agricultural Response of Acidobacteria Present in Two Fynbos Rhizosphere Soils
    (MDPI, 2020-07-10) Conradie, Tersia; Jacobs, Karin
    The Acidobacteria is one of the most abundant phyla in most soil types. Fynbos plants are endemic to South Africa, and these soils provide the ideal habitat for Acidobacteria, because of its low pH and oligotrophic properties. However, little is known about their distribution in the fynbos biome and the impact of cultivation of plants on Acidobacterial diversity. Therefore, the aim of this study was to determine the effect of seasonal changes and cultivation on the relative abundance and diversity of Acidobacteria associated with Aspalathus linearis (rooibos) and Cyclopia spp. (honeybush). This study was based on rhizosphere soil. A total of 32 and 31 operational taxonomic units (OTUs) were identified for honeybush and rooibos, respectively. The majority of these were classified as representatives of subdivisions 1, 2, 3, and 10. Significant differences in community compositions were observed between seasons for both honeybush and rooibos, as well as between the cultivated and uncultivated honeybush. Acidobacteria had a significantly positive correlation with pH, C, Ca2+, and P. In this study, we have shown the effect of seasonal changes, in summer and winter, and cultivation farming on the relative abundance and diversity of Acidobacteria present in the soil of rooibos and honeybush.
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    The soil bacterial communities of South African fynbos riparian ecosystems invaded by Australian Acacia species
    (PLoS, 2014-01-24) Slabbert, Etienne; Jacobs, Shayne Martin; Jacobs, Karin
    Riparian ecosystem along rivers and streams are characterised by lateral and longitudinal ecological gradients and, as a result, harbour unique biodiversity. Riparian ecosystems in the fynbos of the Western Cape, South Africa, are characterised by seasonal dynamics, with summer droughts followed by high flows during winter. The unique hydrology and geomorphology of riparian ecosystems play an important role in shaping these ecosystems. The riparian vegetation in the Western Cape has, however, largely been degraded due to the invasion of non-indigenous plants, in particular Acacia mearnsii, A. saligna and A. dealbata. This study investigated the effect of hydrology and invasion on the bacterial communities associated with fynbos riparian ecosystems. Bacterial communities were characterised with automated ribosomal intergenic spacer analysis (ARISA) and 454 16S rDNA pyrosequencing. Chemical and physical properties of soil within sites were also determined and correlated with community data. Sectioning across the lateral zones revealed significant differences in community composition, and the specific bacterial taxa influenced. Results also showed that the bacterial community structure could be linked to Acacia invasion. The presence of invasive Acacia was correlated with specific bacterial phyla. However, high similarity between cleared and pristine sites suggests that the effect of Acacia on the soil bacterial community structure may not be permanent. This study demonstrates how soil bacterial communities are influenced by hydrological gradients associated with riparian ecosystems and the impact of Acacia invasion on these communities.