Polyphasic taxonomic characterization of lactic acid bacteria isolated from spontaneous sorghum fermentations used to produce ting, a traditional South African food

Ting, an indigenous cooked fermented food made from sorghum flour, is consumed extensively in South Africa. Due to the spontaneous nature of the sorghum fermentation considerable variations in the sensory and microbial quality of the end-product may occur, thus hampering large-scale production of this food. The use of starter cultures purified from the fermented sorghum may be an alternative approach to obtain ting of consistent quality. The aim of this study was therefore to identify the lactic acid bacteria (LAB) associated with ting fermentation using a polyphasic approach. Phenotypic characterization and sequence analysis of the genes encoding the 16S subunit of the ribosomal RNA (rrs) and phenylalanyl tRNA synthase (pheS) were used. The results of these analyses showed that ting fermentation involved at least three different species of LAB, i.e. Lactobacillus fermentum, L. plantarum and L. rhamnosus. To our knowledge, this is the first report of polyphasic taxonomic characterization of LAB from this food. This research forms an essential first step towards the development of relevant starter cultures to produce ting of consistent quality

A mathematical modelling study of fluid flow and mixing in full-scale gas-stirred ladles

A full-scale, three-dimensional, transient mathematical model for application to gas-stirred ladles was developed. Multiphase aspects were accounted for by employing the Lagrangian Discrete Phase Model (DPM) in describing the bubble plume and the Eulerian Volume of Fluid (VOF) model for tracking the free surface of the melt. The standard k (SKE) model was used for modelling turbulence. Further research is required to refine the turbulence modelling approach, but validation experiments showed that the present approach yielded accurate information on bulk fluid flow and mixing in the ladle. The resulting model is easily generalised and computationally efficient. Copyright © 2009, Inderscience Publishers

A numerical modelling investigation into design variables influencing mixing efficiency in full scale gas stirred ladles

A mathematical model of a full scale gas stirred ladle was implemented in designed experiments to assess the influence of various design variables on mixing efficiency. The discrete phase (DPM) and volume of fluid (VOF) models were used in conjunction to describe the different phases and the standard k–ε approach was used for modelling turbulence. Ladle height was identified as the most influential factor in determining mixing efficiency and could be altered by either changing the aspect ratio or the overall scale of the ladle. Gas injection through multiple tuyeres was also identified as a promising strategy for improving mixing, but the success of this strategy depended greatly on the tuyere arrangement. Incorrect tuyere arrangements created significant flow pattern interference in the ladle, which had a detrimental effect on mixing. At high aspect ratios, it was shown that the cross sectional area of the ladle can become too narrow, causing additional flow pattern interference between the rising plumes and the downward recirculating flows

Molecular modelling and simulation studies of the Mycobacterium tuberculosis multidrug efflux pump protein Rv1258c.

Mycobacterial efflux pumps play a major role in the emergence of antimycobacterial drug resistance. Of particular interest is the proteinaceous multi-drug efflux pump protein Rv1258c that encodes a tetracycline/aminoglycoside resistance (TAP-2)-like efflux pump which is active in susceptible and drug resistant Mycobacterium tuberculosis. Rv1258c is implicated in drug resistance to numerous antimycobacterials including first line drugs rifampicin and isoniazid as well as fluoroquinolone and aminoglycoside antibiotic classes. To date, compounds like verapamil and piperine have been shown to inhibit Rv1258c but no direct evidence for binding or mode of action exist. Therefore in the present study we generated an accurate 3D model of Rv1258c using MODELLER and validated its structure using molecular dynamic simulation studies with GROMACS software. The 3D-structures of Rv1258c and the homologous template 1pw4 were simulated within a POPE/POPG lipid bilayer and found to behave similar. Another important finding was the identification of one local energy minima state of the apo protein, which speaks to the flexibility of the protein and will be investigated further. Extraction of one of the open channel conformations of Rv1258c and blind docking of various structurally diverse putative inhibitors and substrates, allowed for the identification of a probable binding site. Spectinamide was found to bind to a different location on the outside surface of the protein suggesting its ability to avoid the efflux channel. We further identified 246 putative compounds that showed higher binding affinity values to Rv1258c compared to piperine and verapamil. Interaction analysis of the top 20 purchasable compounds identified crucial hydrogen bond interactions with Ser26, Ser45 and Glu243 as well as a pi-pi stacking interaction with Trp32 that accounted for the strong affinity of these compounds for Rv1258c. Future studies will entail purchasing a number of compounds for in vitro activity testing against Mycobacterium tuberculosis

Performance of Pleurotus ostreatus mushroom grown on maize stalk residues supplemented with various levels of maize flour and wheat bran

Abstract Improving the performance of mushroom in terms of high production and fast growth rate is essential in mushroom cultivation. In the present study the performance of Pleurotus ostreatus was evaluated using varying levels of wheat bran (WB) and maize flour (MF). The results indicated that Pleurotus ostreatus was highly influenced by different levels of supplementation, with 8% WB, 18% WB and 2% MF having higher contamination rate. The low levels of supplementation gave significantly better mycelial growth rate (MGR) and shorter colonisation period as observed that the control had highest MGR whereby 20% MF had lowest MGR. The pinning time (TP) was shortest at the first flush with minimum of 3 days (12% MF). The higher levels of supplementation showed maximum biological efficiency (BE) such as 14% MF, 12% WB and 14% WB. The yield was also higher at high levels of supplementation such as 20% MF and 8% MF being the exception in the lower levels. Based on the results it was observed that for fast production of oyster mushroom there is no need to supplement the maize stalk substrate but for improved productivity supplements can be added up to certain limits such as 14% MF and 12 WB

Performance of Pleurotus pulmonarius mushroom grown on maize stalk residues supplemented with various levels of maize flour and wheat bran

Abstract The use of supplemented agricultural waste in mushroom cultivation can be one of the environmentally friendly strategies for poverty alleviation. The study evaluated the performance of Pleurotus pulmonarius mushroom grown on maize stalk supplemented with varying levels of wheat bran (WB) and maize flour (MF). A completely random design was used for the experiments. It was observed that Pleurotus pulmonarius was significantly affected by varying levels of supplementation, as 20% WB supplementation encountered higher contamination. The lower supplementation levels gave significantly shorter colonisation period with better mycelial growth rate (MGR). The 2% MF, 2% WB and 4% WB gave significantly higher MGR and faster colonisation. The shortest pinning time (TP) was observed at the first flush with the minimum of 2 days. Higher supplementation levels gave maximum yield and biological efficiency (BE). With further increase of supplementation above a 12% WB and 14% MF, the BE and yield declined. Lower supplementation levels resulted in quicker colonisation period and improved growth rate, whereas high supplementation gave better production in terms of yield and BE. Therefore, for the purpose of maximum production, 12% WB and 14% MF may be recommended while for fast production time, 2% MF and 2% WB are recommended

Polyphasic taxonomic characterization of lactic acid bacteria isolated from spontaneous sorghum fermentations used to produce ting, a traditional South African food

Ting, an indigenous cooked fermented food made from sorghum flour, is consumed extensively in South Africa. Due to the spontaneous nature of the sorghum fermentation considerable variations in the sensory and microbial quality of the end-product may occur, thus hampering large-scale production of this food. The use of starter cultures purified from the fermented sorghum may be an alternative approach to obtain ting of consistent quality. The aim of this study was therefore to identify the lactic acid bacteria (LAB) associated with ting fermentation using a polyphasic approach. Phenotypic characterization and sequence analysis of the genes encoding the 16S subunit of the ribosomal RNA (rrs) and phenylalanyl tRNA synthase (pheS) were used. The results of these analyses showed that ting fermentation involved at least three different species of LAB, i.e. Lactobacillus fermentum, L. plantarum and L. rhamnosus. To our knowledge, this is the first report of polyphasic taxonomic characterization of LAB from this food. This research forms an essential first step towards the development of relevant starter cultures to produce ting of consistent quality

Diversity and dynamics of bacterial populations during spontaneous sorghum fermentations used to produce ting, a South African food

Ting is a spontaneously fermented sorghum food that is popular for its sour taste and unique flavour. Insight of the microbial diversity and population dynamics during sorghum fermentations is an essential component of the development of starter cultures for commercial production of ting. In this study, bacterial populations associated with spontaneous sorghum fermentations were examined using a culture-independent strategy based on denaturing gradient gel electrophoresis and sequence analysis of V3-16S rRNA gene amplicons, and a culture-dependent strategy using conventional isolation based on culturing followed by 16S rRNA and/or pheS gene sequence analysis. The entire fermentation process was monitored over a 54 h period and two phases were observed with respect to pH evolution and microbial succession. The first phase of the process (0–6 h) was characterized by relatively high pH conditions and the presence of Enterococcus mundtii, albeit that this species was only detected with the culture-dependent approach. The second phase of the fermentation process (12–54 h) was characterized by increased acidity and the predominance of a broader range of lactic acid bacteria, including Lactococcus lactis, Lactobacillus fermentum, Lactobacillus plantarum, Lactobacillus rhamnosus, Weissella cibaria, Enterococcus faecalis, and a close relative of Lactobacillus curvatus, as well as some members of the Enterobacteriaceae family. The Lb. curvatus-like species was only detected with PCR-DGGE, while the majority of the other species was only detected using the culture-dependent approach. These findings highlighted the fact that a combination of both approaches was essential in revealing the microbial diversity and dynamics during spontaneous sorghum fermentations