Browsing by Author "Nel, Sanet"

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    Isolation and identification of polysaccharide (gum)-producing bacteria from a sugarcane factory and strategies to prevent their growth
    (Stellenbosch : Stellenbosch University, 2020-03) Nel, Sanet; Dicks, Leon Milner Theodore; Endo, A.; Davis, S. B.; Stellenbosch University. Faculty of Science. Dept. of Microbiology.
    ENGLISH ABSTRACT: Contrary to expectations, Leuconostoc mesenteroides was not the major gum-producing bacterium isolated from sugarcane. Instead, high cell numbers of W. confusa and W. cibaria were recorded. The dominance of Weissella spp. on the prepared cane is significant because these bacteria are not usually associated with deteriorated sugarcane and have not previously been isolated from a sugarcane processing factory. This study also report, for the first time, on the isolation of B. amyloliquefaciens from a sugarcane processing factory. The second aim of the study was to evaluate the efficacy of biocides to prevent/limit microbial growth in the factory. Two dithiocarbamate biocides, Busan®1021 and Preventol®Z, each at a 20 ppm dose, were tested against seven gum-producing bacteria. Preventol®Z demonstrated a bactericidal (killing) effect against Le. mesenteroides A16-9, Le. lactis B9-3, B. subtilis B7-19 and B. amyloliquefaciens B7-51 after 6 h of contact, but had only a bacteriostatic (growth inhibiting) effect on W. cibaria A1-17, W. confusa B1-24 and Lb. fermentum B19-18 when tested under the same conditions. Busan®1021 had a bactericidal effect on all seven species. Bacillus subtilis B7-19 and B. amyloliquefaciens B7-51 were susceptible to both biocides, but only for the first 2 h of exposure, after which the killing effect remained constant. Based on results obtained in this study, the concentrations of Preventol®Z and Busan®1021 may need to be increased, or dosage intervals altered, to kill all gum-producing bacteria. Although sugarcane processing factories have little to no control over the quality of cane entering the factory, poor sanitation in the factory and incorrect process control can also contribute to sucrose loss due to microbial activities and subsequent gum formation. Factories should therefore be mindful of correctly controlling high-temperature processes and reduce the recirculation of sump contents which are not treated with biocides. This study provided valuable knowledge on the identities of gum-producing bacteria in sugarcane processing factories, and their susceptibility to two commercial biocides.
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    Phylogenetic analysis of leuconostoc and lactobacillus species isolated from sugarcane processing streams
    (Wiley Open Access, 2020) Nel, Sanet; Davis, Stephen B.; Endo, Akihito; Dicks, Leon Milner Theodore, 1961-
    High levels of gums such as dextran, produced by Leuconostoc and Lactobacillus spp., have a severe impact on factory throughput and sugar quality. This study aimed to determine the phylogenetic relationships between gum‐producing Leuconostoc and Lactobacillus bacteria which were isolated from various locations in a sugarcane processing factory at times when low‐ and high‐dextran raw sugar, respectively, were produced. Phylogenetic analysis of 16S rRNA gene sequences grouped 81 isolates with the type strains of Leuconostoc mesenteroides (subspp. mesenteroides , dextranicum, and cremoris ), Leuconostoc pseudomesenteroides, Leuconostoc lactis, and Leuconostoc citreum , respectively. Forty‐three isolates clustered with the type strain of Lactobacillus fermentum . The phylogenetic relatedness of the isolates was determined by sequencing and analysis of the housekeeping genes rpoA and dnaA for Leuconostoc spp. and the pheS and tuf genes for the Lactobacillus spp. The rpoA gene proved discriminatory for the phylogenetic resolution of all of the isolated Leuconostoc spp. and the dnaA housekeeping gene was shown to be effective for isolates clustering with the type strains of Leuc. mesenteroides and Leuc. citreum . None of the loci examined permitted differentiation at the subspecies level of Leuc. mesenteroides . Single‐locus analysis, as well as the concatenation of the pheS and tuf housekeeping gene sequences, yielded identical phylogenies for the Lactobacillus isolates corresponding to L. fermentum.