Date of Completion

2024

Document Type

Thesis

Degree Name

Bachelor of Science in Biochemistry

Keywords

Lacticaseibacillus casei, gut microbiota, Zn2+, Mn2+, Co2+, homeostasis

Abstract

The interplay between diet and human gut microbiota is paramount in elucidating the molecular dynamics of human health. Proper nutrition from diet includes a complex mixture of essential trace metal ions having numerous biological properties in intermediary metabolism and enzymatic mechanisms. These metal ion-specific biological functions, in turn, may be associated to the overall abundance of gut microbiota affecting both the bacteria and human intestinal homeostasis. Although the molecular effects of individual metal cations have been established, the effects of a threecomponent trace metal ion mixture comprising Zn2+, Mn2+, and Co2+ on Lacticaseibacillus casei, a representative probiotic human gut bacterium, remain elusive. This study investigated the influence of these trace metals, both individually and as mixtures, on the growth of wild-type L. casei. The result of the antimicrobial assay demonstrated a general decline in L. casei viability with treatments containing 0 to 100 ppm of Co2+, 0 to 500 ppm of Mn2+, and 0 to 750 ppm of Zn2+. Findings revealed that L. casei had lower tolerance for Co2+ (MIC50 = 10.04 ± 0.0827 ppm) than Mn2+ (MIC50 = 24.63 ± 0.1015 ppm) and Zn2+ (MIC50 = 129.17 ± 0.0690 ppm). Among the 18 mixtures, statistical analyses via ANOVA and post-hoc Bonferroni test showed significant differences in viability between Mixture 6 and 17 (p < 0.05) which elicited the strongest and weakest inhibitory effects on L. casei growth, respectively. Scanning electron microscopy (SEM) images revealed corrugations in L. casei surface membrane topology after exposure to Mixture 6. Zn2+-treated cells displayed apoptotic-like features and cellular debris, while Mn2+- and Co2+-treated cells exhibited cell splitting at MIC50. Overall, our findings elucidated L. casei tolerance to Zn2+, Mn2+, and Co2+, and their mixtures, under nutrient-sufficient conditions. Further investigations should focus on (1) the effects of varying essential trace metal ion concentrations on the composition and function of the gut microbiome through sequencing techniques and (2) physiologically relevant biotechnological applications to improve probiotic L. casei design under extreme metal doses.

First Advisor

Nedrick T. Distor

Second Advisor

Walter Aljhon T. Espiritu

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