Isolation of Putative Lactic Acid Bacteria From Yacon (Smallanthus sonchifolius) Plants

Abstract

This study aimed to isolate, enumerate, and characterize lactic acid bacteria (LAB) from Smallanthus sonchifolius (yacon) tissues using selective enrichment strategies, and to evaluate the efficacy of molasses-based fermentation in enhancing LAB proliferation for potential probiotic applications. Fresh plant parts—including leaves, stems, tubers, and roots—were processed for microbial recovery using peptone water extraction and subsequently plated on De Man, Rogosa, and Sharpe (MRS) agar, a medium selective for acidophilic, fastidious LAB. Initial colony-forming unit (CFU) counts revealed limited native LAB in fresh samples, with highest counts observed in roots (up to 26 CFU at 10¹), suggesting rhizosphere-mediated microbial colonization. A separate batch of identical tissues was subjected to molasses-based fermentation under controlled anaerobic conditions for 14 days, resulting in significant microbial enrichment. Stem samples yielded the highest post-fermentation counts (up to 152 CFU at 10¹), with detectable LAB populations in previously low-yielding tissues such as leaves and tubers. Selected colonies exhibited uniform creamy-white pigmentation, entire margins, smooth surfaces, and flat to raised elevations. Gram staining and catalase testing confirmed all isolates to be Gram-positive and catalase-negative—definitive phenotypic traits of LAB. Microscopy revealed coccoid to bacilliform cell morphologies, indicative of genera such as Lactococcus, Leuconostoc, Lactobacillus, Saccharomyces. The data substantiate molasses-based fermentation as a selective ecological pressure that enriches acid-tolerant, metabolically active LAB populations from plant matrices. This work supports the exploitation of fermented yacon as a novel matrix for LAB bioprospecting and provides a foundation for downstream probiotic screening, functional genomic analysis, and biotechnological formulation.