ABSTRACT
Research background: Lactic acid bacteria (LAB) are known to produce folate. However, this ability is highly strain-dependent. Folate synthesis in specific LAB strains is affected by the availability of folate, which can be consumed by other LAB under certain conditions. Moreover, differences in folate synthesis capabilities are related to the presence of folate biosynthesis-related genes and regulation of this pathway. Experimental approach: As basic information to better understand the regulation of folate biosynthesis among different LAB species and strains, folate biosynthetic genes were screened and identified in folate-producing and non-folate-producing LAB isolated from various local food sources in Indonesia. The extracellular folate productivity amounts of the isolates were analyzed using high-performance liquid chromatography with a diode array detector (HPLC-DAD). Results and conclusions: Eleven of the thirteen tested LAB isolates had all of the eight genes involved in folate biosynthesis (folE, folQ, folB, folK, folP, folC1, folA and folC2). Furthermore, these isolates produced extracellular folate ranging from 10.37 to 31.10 µg/mL. In contrast, two non-folate-producing isolates lacked several folate biosynthetic genes, such as folQ, folP and folA, which is possibly the reason for their inability to synthesize folate de novo. Phylogenetic tree construction revealed that the folate biosynthetic genes (excluding folK and folP) from six distinct species of folate-producing LAB isolates were monophyletic with homologous genes from other LAB species in the database. Novelty and scientific contribution: In this study, the distribution of folate biosynthetic genes in various LAB species was determined. The findings from this research support the use of folate biosynthesis marker genes in the genotypic screening for folate-producing LAB.
ABSTRACT
Folate (vitamin B9) is an essential nutrient for cell metabolism, especially in pregnant women; however, folate deficiency is a major global health issue. To address this issue, folate-rich fermented foods have been used as alternative sources of natural folate. Lactic acid bacteria (LAB), which are commonly involved in food fermentation, can synthesize and excrete folate into the medium, thereby increasing folate levels. However, screening for folate-producing LAB strains is necessary because this ability is highly dependent on the bacterial strain. Some strains of LAB consume folate, and their presence in a fermentation mix can lower the folate levels of the final product. Since microorganisms efficiently regulate folate biosynthesis to meet their growth needs, some strains of folate-producing LAB can deplete folate levels if folate is available in the media. Such folate-efficient producers possess a feedback inhibition mechanism that downregulates folate biosynthesis. Therefore, the application of folate-overproducing strains may be a key strategy for increasing folate levels in media with or without available folate. Many studies have been conducted to screen folate-producing bacteria, but very few have focused on the identification of overproducers. This is probably because of the limited understanding of the regulation of folate biosynthesis in LAB. In this review, we discuss the roles of folate-biosynthetic genes and their contributions to the ability of LAB to synthesize and regulate folate. In addition, we present various hypotheses regarding the regulation of the feedback inhibition mechanism of folate-biosynthetic enzymes and discuss strategies for obtaining folate-overproducing LAB strains.
ABSTRACT
Folates are essential micronutrients, and folate deficiency still occurs in many countries. Lactic acid bacteria (LAB) are known to be able to synthesize folates during fermentation, but the folate production is strain-dependent and influenced by the fermentation medium, presence of a folate precursor, and fermentation time. This study aimed to screen extracellular folate-producing LAB from local food sources and evaluate the factors influencing their folate biosynthesis during milk fermentation. The selection of folate-producing LAB was based on their ability to grow in folate-free medium (FACM), with folate concentrations quantified by microbiological assay. Growth of the 18 LAB in FACM varied between isolates, with only 8 isolates growing well and able to synthesize extracellular folate at relatively high concentrations (up to 24.27 ng/mL). The isolates with highest extracellular folate levels, Lactobacillus fermentum JK13 from kefir granules, Lactobacillus plantarum 4C261 from salted mustard, and Lactobacillus rhamnosus R23 from breast milk, were applied to milk fermentation. The last two isolates were probiotic candidates. The three isolates consumed folate when it was present in the milk, and its consumption was in line with their growth. The availability of folate precursors affected the amount of folate consumed, but did not lead to increased folate concentrations in the medium after 72 h fermentation. The results of this study indicate that these isolates cannot be utilized for producing folate in folate-containing milk, as it shows feedback inhibition on folate biosynthesis.
