Felicitas Pswarayi | ALES Graduate Seminar

Date(s) - 08/12/2021
8:00 am - 9:00 am

Event details:  A graduate exam seminar is a presentation of the student’s final research project for their degree.

This is an ALES PhD Final Exam Seminar by Felicitas Pswarayi.  This seminar is open to the general public to attend.

Thesis Topic:

Characterization of Mahewu, a Traditional Fermented Cereal Beverage from Zimbabwe, as a Source of Functional Lactobacilli

Public Seminar: https://ualberta-ca.zoom.us/j/99948227523

PhD with Dr. Michael Gaenzle

Seminar Abstract:

In Africa the diversity of non-alcoholic fermented cereal beverages with live microbiota is much larger than anywhere else in the world. Mahewu is a non-alcoholic fermented beverage produced at the household level in Zimbabwe. It is prepared by cooking maize porridge which is then fermented with millet malt at ambient temperature. What is unique and different in Africa compared to other areas of the world is the occurrence of diverse non-alcoholic beverages with live microbiota and the widespread use of fermented porridges based on maize, millet or sorghum. Whereas fermented foods produced in Europe and North America usually depend on defined starter cultures, those made in sub-Saharan Africa predominantly, but not exclusively, rely on spontaneous fermentations with some back-slopping and are produced at the household level. African fermented cereal products are much less well characterized than fermentations in developed countries and starter cultures developed from African traditional fermented cereal foods are scarcely available, if at all. Therefore, the aim of this research program was to characterize lactic acid bacteria isolated from mahewu and to determine their potential as functional lactobacilli in fermented cereal foods to counteract the poor sanitation endemic in developing countries.

The mahewu microbiota consisted of 3 to 7 dominant strains of lactobacilli and two strains of yeasts. A unique feature, one putative exopolysaccharide gene cluster was identified in the genome of Limosilactobacillus fermentum FUA3588. Millet malt contained 8 to 19 strains of Enterobacteriaceae, lactobacilli, bacilli, and very few yeasts. Millet malt was confirmed as the major source of mahewu microbiota, and is the only raw ingredient used in the production of mahewu. Therefore, mahewu contains both viable probiotic fermentation organisms and viable opportunistic pathogens which together may positively and negatively affect the health of consumers. Model mahewu fermentations demonstrated that minor components of the malt microbiota, Limosilactobacillus fermentum and Lactiplantibacillus plantarum, rapidly outcompete Enterobacteriaceae and Bacillus species during the fermentation.

Comparative genomics revealed that plant-associated phylogenetically diverse lactobacilli from cereal fermentations share plasmid-encoded multidrug resistance (MDR) transporters with a putative function in resistance to antimicrobials. Several lines of evidence support a connection between antimicrobial plant secondary metabolites, MDR transporters, and resistance to antimicrobial compounds by cereal-associated lactobacilli: (i) multiple MDR transport genes, termed millet phenolics resistance (mpr) genes, are part of the core genome of Lp. plantarum and Lm. fermentum, lactobacilli that are adapted to plants and thus encounter phenolic compounds in their habitat; (ii) Lp. plantarum and Lm. fermentum are resistant to multiple natural antimicrobial compounds and antibiotics; (iii) genes encoding for MDR transporters are over-expressed during growth in cereal substrates.

The findings presented in this thesis provide comprehensive knowledge of the microbiota of mahewu and millet malt and a better understanding of spontaneous cereal fermentations. This can lead to the selection and development of functional and probiotic starter cultures that may be used to mitigate the risks associated with uncontrolled cereal fermentation processes.