Date of Award

12-11-2025

Degree Type

Thesis

Degree Name

Master of Food and Animal Sciences (M.S.)

Department

Agricultural and Environmental Sciences

First Advisor

Brahmaiah Pendyala

Abstract

Overexploitation of antibiotics in the animal industry has driven the need for reduced usage, but this reduction has intensified the challenge posed by Salmonella enterica and Campylobacter jejuni to livestock systems and public health. This situation underlines the need for sustainable antimicrobial alternatives. Although cyanobacteria are promising in this respect, since they may produce a variety of bioactive metabolites, the amounts of these metabolites in their natural state are insufficient to elicit potent antibacterial action. In this study, autofermentation was investigated as a means of enhancing antibacterial efficacy in Fischerella ambigua and Nostoc muscorum by promoting the synthesis of organic acids. In F. ambigua, total organic acid production increased from 9.19 g/L at pH 8.4 (~36.8% conversion from 25 g/L biomass) to 13.25 g/L at pH 10.1 (~53% conversion), with acetic and butyric acids as the dominant organic acids. N. muscorum also showed a similar trend, at pH 8.4, 35 g/L biomass yielded 10.63 g/L total acids (~35.4% conversion), while at pH 10.1 the yield rose to 19.18 g/L (~54.86% conversion), predominantly butyric acid. The aqueous extract of F. ambigua inhibited S. enterica at 1.66 g/L and C. jejuni at 3.31 g/L, while N. muscorum required 2.40 g/L and 4.80 g/L, respectively. The pH of the extracts was adjusted to 4.9 to mimic gut conditions, ensuring that the organic acids were present in their protonated (acid) form rather than as salts. Autofermentation further enhanced the methanolic extract's antibacterial potency. F. ambigua inhibited S. enterica at 3 mg/mL (fresh extracts: 6 mg/mL) and C. jejuni at 4 mg/mL (fresh extracts: 7 mg/mL), whereas autofermented N. muscorum inhibited S. enterica at <1 mg/mL (fresh extracts: 4 mg/mL) and C. jejuni at 2 mg/mL (fresh extracts: 4 mg/mL). These results demonstrate that autofermentation substantially improves organic acid accumulation and antibacterial efficacy, highlighting the potential of these cyanobacteria as sustainable feed-based antimicrobial agents.

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