Vuyo Mavumengwana

Review on Microbial Degradation of Aflatoxins.

ABSTRACT Aflatoxin (AF) contamination presents one of the most insidious challenges to combat, in food safety. Its adulteration of agricultural commodities presents an important safety concern as evident in the incidences of its health implication and economic losses reported widely. Due to the overarching challenges presented by the contamination of AFs in foods and feeds, there is an urgent need to evolve cost-effective and competent strategies to combat this menace. In our review, we tried to appraise the cost-effective methods for decontamination of AFs. We identified the missing links in adopting microbial degradation as a palliative to decontamination of AFs and its commercialization in food and feed industries. Cogent areas of further research were also highlighted in the review paper.

Aflatoxin B1 degradation by liquid cultures and lysates of three bacterial strains

Aflatoxin contamination remains a daunting issue to address in food safety. In spite of the efforts geared towards prevention and elimination of this toxin, it still persists in agricultural commodities. This has necessitated the search for other measures such as microbial degradation to combat this hazard. In this study, we investigated the biodegradation of aflatoxin B1 (AFB1), using lysates of three bacterial strains (Pseudomonas anguilliseptica VGF1, Pseudomonas fluorescens and Staphylococcus sp. VGF2) isolated from a gold mine aquifer. The bacterial cells were intermittently lysed in the presence and absence of protease inhibitors to obtain protease free lysates, subsequently incubated with AFB1 for 3, 6, 12, 24, and 48h to investigate whether any possible AFB1 degradation occurred using high performance liquid chromatography (HPLC) for detection. Results obtained revealed that after 6h of incubation, protease inhibited lysates of Staphylococcus sp. VGF2 demonstrated the highest degradation capacity of 100%, whereas P. anguilliseptica VGF1 and P. fluorescens lysates degraded AFB1 by 66.5 and 63%, respectively. After further incubation to 12h, no residual AFB1 was detected for all the lysates. Lower degrading ability was however observed for liquid cultures and uninhibited lysates. Data on cytotoxicity studies against human lymphocytes showed that the degraded products were less toxic than the parent AFB1. From this study, it can thus be deduced that the mechanism of degradation by these bacterial lysates is enzymatic. This study shows the efficacy of crude bacterial lysates for detoxifying AFB1 indicating potential for application in the food and feed industry.

Clayey minerals and clayey soils as possible microorganism repositories

Clay minerals are one of the most abundant and crucial structural materials of the Earth’s crust, playing a significant role in many aspects of life. The present study aims to critically investigate the presence of microorganisms within different clayey soil samples. Microorganisms are ubiquitous by nature due to their natural ability to adapt to different habitats. Bacteria and Archea are the most abundant microorganisms in the soil and serve many important roles like nitrogen fixation. Fungi are also an integral part of the soil micro flora as they serve as food sources to other organisms as well as facilitate as layer organisms with beneficial relationships to plants. The continued evolution of man and subsequent use of clayey soils in areas such as pottery, cosmetics, engineering and geophagia brings into question whether microorganisms are harmful. Soil samples with high amounts of fine particles and colloidal substances were studied while taking into account the identified hydrated aluminosilicates and their roles in bioavailability. The study also investigated the possible types of microbial flora associated with each type of clayey soil as well as their functions within the human body. Considering the diverse origin of these microorganisms, we discuss their modes of attachment to clayey soils with the aim of minimising their transmission to humans.

In vitro biomass accumulation of calli and root enhancement of Leucas aspera (Willed) Linn. under stress conditions

Leucas aspera is a high value medicinal plant in India, Java, Mauritius and Philippines. The effects of plant growth regulators effects on in vitro callus biomass accumulation and root enhancement were assessed using leaf and stem explants. Leaf and stem explants were cultured on Murashige and Skoog basal medium supplemented with different concentrations of auxins and cytokinins. The highest amount of callus biomass accumulation was observed on leaf explants. Comparisons between stem and leaf explants indicated that leaf explants showed the greatest callus formation. Greatest callus formation was observed on NAA (2 mg L−1) (79.22%), followed by 2,4-D (2.0 mg L−1) (70.11%) and IBA (2.0 mg L−1) showed the least formation (36.42%). Maximum callus formation was observed on stem explants; these showed 60.70% from 2,4-D (2 mg L−1), NAA (2 mg L−1) showed 40.16%, and far less was obtained on IBA (31.60%). The greatest root formation (75.32%) was obtained on IBA (2 mg L−1) and the number of roots per shoot obtained was 26.55%; IAA (2 mg L−1) showed 66.82% root formation and the number of roots obtained was 21.22%; NAA (2 mg L−1) showed 54.33% root formation. In conclusion, root enhancement increased best under dark conditions, the conditions most suitable for regeneration of large numbers of high value clonal plants for commercial production and isolation of bioactive compounds.