Browsing by Author "Mbukwa, Elbert A."

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    PCR Amplification and DNA Sequence of Mcya Gene: The Distribution Profile of a Toxigenic Microcystis Aeruginosa in the Hartbeespoort Dam, South Africa
    (2013) Mbukwa, Elbert A.; Boussiba, Sammy; Wepener, Victor; Leu, Stefan; Kaye, Yuval; Msagati, Titus A. M.; Mamba, Bhekie B.
    Using new polymerase chain reaction (PCR) primers, a once known to be under-transcribed microcystin synthetase A (mcyA) gene from the only known toxigenic cyanobacterium Microcystis aeruginosa dominating the Hartbeespoort Dam was consistently amplified from genomic DNA extracted from a set of algal and cell free water samples collected across this dam. In addition to this, five more mcy genes (mcyBCDEG) were also amplified during this study. The resultant mcyA PCR products (518 bp) were purified and sequenced and gave nucleotide sequence segments of 408 bp sizes. The obtained sequence was aligned to the published mcyA gene sequence available online on the NCBI database and resulted in 100% similarity to a 408 bp mcyA gene sequence segment of M. aeruginosa UWOCC RID-1. Furthermore, it was found that the above sequence segment (408 bp) spans from a common base in M. aeruginosa PCC 7806 and M. aeruginosa PCC 7820 from 141 to 548 bp in the N-methyl transferase (NMT) region signifying their closer relatedness to M. aeruginosa UWOCC strains. This study has for the first time amplified mcyA gene consistently from both intracellular and extracellular DNA extracts obtained from algal and cell free water samples, respectively. Sequence data and the amplified mcy genes showed that M. aeruginosa is widely distributed and dominant in this dam.
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    Phytochemical Constituents of Vangueria Infausta: Their Radical Scavenging and Antimicrobial Activities
    (2007-01) Mbukwa, Elbert A.; Chacha, Musa; Majinda, Runner R. T.
    A new biflavonoid, 5,7,3',5'',7'',4'''-hexahydroxy (4'-O-3''')-biflavone (1) and a polyketide derivative, methylcylohex-1-ene (3) [previously reported only as a synthetic compound] were isolated from aerial parts of Vangueria infausta. In addition, eight other known flavonoids viz. (-)-epicatechin, epiafzelechin, dihydrokaempferol, quercetin, luteolin (2), dihydroquercetin-3'-O-glucoside, daidzein and genistein were also isolated from this plant. Structures were identified using 1D-and 2D NMR experiments as well as ESI-MS, IR and UV spectra. The new biflavonoid 1 showed higher radical scavenging activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH) reagent compared to ascorbic acid (standard) using a spectrophotometric method. Compound 1 was less sensitive to Gram-positive and Gram-negative bacterial strains and yeast (Candida mycoderma) compared to luteolin and quercetin on the Bioautographic Agar Overlay Assay.
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    Potential Use of Dissolved Cyanobacterial DNA for Monitoring Toxic Microcystis Cyanobacteria in Filtered Water
    (Elsevier, 2013-07) Mbukwa, Elbert A.; Boussiba, Sammy; Wepener, Victor; Leu, Stefan; Kaye, Yuval; Msagati, Titus A. M.; Mamba, Bhekie B.
    Toxic and non-toxic Microcystis sp. are morphologically indistinguishable cyanobacteria that are increasingly posing health problems in fresh water systems by producing odours and/or toxins. Toxic Microcystis sp. produces toxicologically stable water soluble toxic compounds called microcystins (MCs) that have been associated with cases of aquatic life and wildlife poisoning and kills including some cases of human illnesses/deaths around the world. Thus, the need for rapid detection of toxic Microcystis sp. in surface water is imperatively a necessity for early mitigation purposes. Genomic DNA from potentially toxic Microcystis sp. comprises of ten microcystin synthetase (mcy) genes of which six major ones are directly involved in MCs biosynthesis. In Polymerase Chain Reaction (PCR) methodsmcy genes can be amplified from intracellular/extracellular genomic DNA using PCR primers. However, little is known about the limitations of sourcing genomic DNA templates from extracellular DNA dissolved in water. In this work, filtered water (0.45 lM) from a Microcystis infested Dam (South Africa) was re-filtered on 0.22 lM syringe filters followed by genomic DNA isolation and purification from micro-filtrates (9 mL). Six major mcy genes (mcyABCDEG) from the isolated DNA were amplified using newly designed as well as existing primers identified from literature. PCR products were separated by gel electrophoresis and visualized after staining with ethidium bromide. The limitation of using dissolved DNA for amplification of mcy genes was qualitatively studied by establishing the relationship between input DNA concentrations (10.0–0.001 ng/lL) and the formation of respective PCR products. The amplification of mcyA gene using new primers with as little as 0.001 ng/lL of DNA was possible. Other mcy gene sensitivities reached 0.1 ng/lL DNA dilution limits. These results demonstrated that with appropriately optimized PCR conditions the method can provide accurate cost-effective tools for rapid detection of toxic Microcystis sp. in water giving early information for water quality monitoring against MC producing cyanobacteria.
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    Preparation of Guanidinium Terminus-Molecularly Imprinted Polymers for Selective Recognition and Solid-Phase Extraction (SPE) of [Arginine]-Microcystins
    (Springer Link, 2013) Mbukwa, Elbert A.; Msagati, Titus A. M.; Mamba, Bhekie B.
    About 70 % of microcystin (MC) congeners reported in literature consist of L-arginine amino acid (R) with its guanidinium terminal extending out of the cyclic moiety of these MCs. Molecularly imprinted polymer (MIP) bearing guanidinium terminus cavities was successfully synthesised using L-arginine as a template. Non-imprinted polymer (NIP; without template) was also synthesised for control purposes. The surface area, total pore volume and average pore diameter of MIP and NIP were 267.13 m(2)/g, 0.63 cm(3)/g and 88.39 Å; 249.39 m(2)/g; 0.54 cm(3)/g and 87.14 Å, respectively. The polymers were investigated for selective recognition and extraction of [arginine]-MCs in water using solid-phase extraction/liquid chromatography-electrospray ionisation-mass spectrometry (SPE/LC-ESI-MS) method. Representative model standard solutions (0.5-10.0 μg/L) of MC-LR and MC-LY were spiked in distilled water, recovered by SPE and quantified by LC-ESI-MS. In this study, Oasis Waters™ HLB cartridges served as positive control SPE sorbents. The MIP recognised MC-LR with high recoveries (70.8-91.4 %; r(2) = 0.9962) comparable to HLB cartridges (71.0-91.85 %; r(2) = 0.9993), whereas the NIP did not recognise or retain MC-LR. Also, neither MIP nor NIP recognised or retained MC-LY. Extracts of environmental toxic Microcystis aeruginosa were subjected to SPE procedure employing MIP, NIP and HLB cartridges. Microcystin-LR, -YR, -RR, -WR, -(H4)YR and (D-Asp(3), Dha(7))MC-RR were extracted by MIP and HLB cartridges only as confirmed by LC-ESI-MS. This study demonstrated that the prepared MIP have potential applications for the removal in water and LC-ESI-MS identifications of MCs consisting the guanidinium moiety, i.e.[arginine]-MCs, and in particular targeting commonly encountered toxic congeners, MC-LR, -YR and -RR.
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    Quantitative Variations of Intracellular Microcystin-LR, -RR and -YR in Samples Collected from Four Locations in Hartbeespoort Dam in North West Province (South Africa) During the 2010/2011 Summer Season
    (2012) Mbukwa, Elbert A.; Msagati, Titus A. M.; Mamba, Bhekie B.
    Abstract: The Hartbeespoort (HBP) Dam is a reservoir used for agricultural, domestic supply of raw potable water and recreational activities in South Africa’s North-West Province. Eutrophication and cyanobacterial blooms have long been a cause of water-quality problems in this reservoir. The most prevalent bloom-forming species is Microcystis aeruginosa, often producing the toxin microcystin, a hepatotoxin which can negatively impact aquatic animal and human health, and poses a problem for potable water supply. Algal samples were collected monthly from four pre-determined sites in the dam during the summer months (December 2010–March 2011). Intracellular microcystins (MCs) were extracted using SPE C18 cartridges, followed by separation, identification and quantification using LC-ESI-MS techniques. Quantitative variation studies of MCs were conducted with respect to MC congener isolated, sampling site and month. Three main MC congeners (MC-RR, -LR and-YR) were isolated, identified and quantified. In addition, three minor MCs (MC-WR, MC-(H4)YR and (D-Asp3, Dha7)MC-RR were also identified, but were not quantified. The MC dominance followed the order MC-RR>MC-LR>MC-YR across all sites and time. The maximum and minimum concentrations were 268 µg/g and 0.14 µg/g DW for MC-RR and MC-YR, respectively, of the total MCs quantified from this study. One-way ANOVA showed that there were no significant differences between average MC concentrations recorded across months (P = 0.62), there was, however, a marginally-significant difference in concentrations among MC congeners (P = 0.06). ANCOVA revealed a highly significant interaction between sites and MC congeners on MC concentration (P < 0.001).
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    Supported Liquid Membrane-Liquid Chromatography-Mass Spectrometry Analysis of Cyanobacterial Toxins in Fresh Water Systems
    (Elsevier, 2012) Mbukwa, Elbert A.; Msagati, Titus A. M.; Mamba, Bhekie B.
    Harmful algal blooms (HABs) are increasingly becoming of great concern to water resources worldwide due to indiscriminate waste disposal habits resulting in water pollution and eutrophication. When cyanobacterial cells lyse (burst) they release toxins called microcystins (MCs) that are well known for their hepatotoxicity (causing liver damage) and have been found in eutrophic lakes, rivers, wastewater ponds and other water reservoirs. Prolonged exposure to low concentrated MCs are equally of health importance as they are known to be bioaccumulative and even at such low concentration do exhibit toxic effects to aquatic animals, wildlife and human liver cells. The application of common treatment processes for drinking water sourced from HABs infested reservoirs have the potential to cause algal cell lyses releasing low to higher amounts of MCs in finished water. Trace microcystins in water/tissue can be analyzed and quantified using Liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) following solid-phase extraction (SPE) sample clean-up procedures. However, extracting MCs from algal samples which are rich in chlorophyll pigments and other organic matrices the SPE method suffers a number of drawbacks, including cartridge clogging, long procedural steps and use of larger volumes of extraction solvents. We applied a supported liquid membrane (SLM) based technique as an alternative sample clean-up method for LC-ESI-MS analysis of MCs from both water and algal cells. Four (4) MC variants (MC-RR, -YR, -LR and -WR) from lyophilized cells of Microcystis aeruginosa and water collected from a wastewater pond were identified) and quantified using LC-ESI-MS following a SLM extraction and liquid partitioning step, however, MC-WR was not detected from water extracts. Within 45 min of SLM extraction all studied MCs were extracted and pre-concentrated in approximately 15 μL of an acceptor phase at an optimal pH 2.02 of the donor phase (sample). The highest total quantifiable intracellular and extracellular MCs were 37.039 ± 0.087 μg/g DW and 5.123 ± 0.018 μg/L, respectively. The concentrations of MC-RR were the highest from all samples studied recording maximum values of 21.579 ± 0.066 μg/g DW and 3.199 ± 0.012 μg/L for intracellular and extracellular quantities, respectively.
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    Synthesis and Antimicrobial Activity of New 2-Azetidinones from N-(Salicylidene) Amines and 2-Diazo-1, 2-Diarylethanones
    (2007) Singh, Girija S.; Mbukwa, Elbert A.; Pheko, Tshepo
    This paper describes the reactions of N-salicylideneamines with diarylketenes generated from thermal decomposition of the 2-diazo-1,2- diarylethanones. An equimolar reaction of the N-salicylidenebenzhydrylamine with diphenylketene affords a mixture of 2-[(benzhydrylimino)methyl]phenyl-2,2- diphenylacetate as a major product and 1-benzhydryl-3,3-diphenyl-4-[2′-(O- diphenylacyl)hydroxyphenyl]-2-azetidinone as a minor product. The reactions of various N-salicylideneamines with 2.2 molar equivalents of 2-diazo-1,2- diarylethanones have been carried out to afford 1-substituted-3,3-diaryl-4- [2′-(O-diarylacyl)hydroxyphenyl]-2-azetidinones as sole product in excellent yields. The products, characterized on the basis of satisfactory analytical and spectral data, have shown moderate to good antimicrobial activity against some bacteria and fungi. Among the fourteen compounds in the series, the 2-azetidinone 4l with a 4-chlorophenyl group on β-lactam ring nitrogen and 4-methylphenyl groups on β-lactam ring C-3 position is the most active compound.
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    Vangueria Infausta Root Bark: In Vivo and in Vitro Antiplasmodial Activity
    (2006-02) Abosl, A. O.; Mbukwa, Elbert A.; Majinda, Runner R. T.; Raserok, B. H.; Yenesew, Abiy; Midiwo, Jacob O.; Akala, Hoseah; Liyala, Pamela; Waters, Norman C.
    Vangueria infausta burch subsp. infausta (Rubiaceae) produces fruits eaten by humans and animals. The leaf, fruit, stem bark and root bark are used as a remedy for many ailments and the roots are used to treat malaria. In this study, concentrations of fractions of the V. infausta root bark extract that produce 50% inhibition (IC50) are determined using the ability of the extract to inhibit the uptake of [G3H]-hypoxanthine by P. falciparum cultured in vitro. The root bark extract showed antimalarial activity against Plasmodium berghei in mice. It gave a parasite suppression of 73.5% in early infection and a repository effect of 88.7%. One fraction obtained from a chloroform extract gave an IC50 value of 3.8 +/- 1.5 microg/mL and 4.5 +/- 2.3 microg/mL against D6 and W2 strains of P. falciparum, respectively, and another from the butanol extract gave an IC50 value of 3.9 +/- 0.3 microg/mL against the D6 strain. Chloroquine had an IC50 value of 0.016 microg/mL and 0.029 microg/mL against D6 and W2 strains, respectively. The plant showed the presence of flavonoids, coumarins, tannins, terpenoids, anthraquinones and saponins.Vangueria infausta burch subsp. infausta (Rubiaceae) produces fruits eaten by humans and animals. The leaf, fruit, stem bark and root bark are used as a remedy for many ailments and the roots are used to treat malaria. In this study, concentrations of fractions of the V. infausta root bark extract that produce 50% inhibition (IC50) are determined using the ability of the extract to inhibit the uptake of [G3H]-hypoxanthine by P. falciparum cultured in vitro. The root bark extract showed antimalarial activity against Plasmodium berghei in mice. It gave a parasite suppression of 73.5% in early infection and a repository effect of 88.7%. One fraction obtained from a chloroform extract gave an IC50 value of 3.8 +/- 1.5 microg/mL and 4.5 +/- 2.3 microg/mL against D6 and W2 strains of P. falciparum, respectively, and another from the butanol extract gave an IC50 value of 3.9 +/- 0.3 microg/mL against the D6 strain. Chloroquine had an IC50 value of 0.016 microg/mL and 0.029 microg/mL against D6 and W2 strains, respectively. The plant showed the presence of flavonoids, coumarins, tannins, terpenoids, anthraquinones and saponins.