ABSTRACT
With its estrogenic activity, (
S
)-equol plays an important role in maintaining host health and preventing estrogen-related diseases. Exclusive production occurs through the transformation of soy isoflavones by intestinal bacteria, but the reasons for variations in (
S
)-equol production among different individuals and species remain unclear. Here, fecal samples from humans, pigs, chickens, mice, and rats were used as research objects. The concentrations of (
S
)-equol, along with the genetic homology and evolutionary relationships of (
S
)-equol production-related genes [daidzein reductase (DZNR), daidzein racemase (DDRC), dihydrodaidzein reductase (DHDR), tetrahydrodaidzein reductase (THDR)], were analyzed. Additionally,
in vitro
functional verification of the newly identified DDRC gene was conducted. It was found that approximately 40% of human samples contained (
S
)-equol, whereas 100% of samples from other species contained (
S
)-equol. However, there were significant variations in (
S)-
equol content among the different species: rats > pigs > chickens > mice > humans. The distributions of the four genes displayed species-specific patterns. High detection rates across various species were exhibited by
DHDR
,
THDR
, and
DDRC
. In contrast, substantial variations in detection rates among different species and individuals were observed with respect to
DZNR
. It appears that various types of
DZNR
may be associated with different concentrations of (
S)-
equol, which potentially correspond to the regulatory role during (
S)-
equol synthesis. This enhances our understanding of individual variations in (
S
)-equol production and their connection with functional genes
in vitro
. Moreover, the newly identified DDRC exhibits higher potential for (
S)-
equol synthesis compared to the known DDRC, providing valuable resources for advancing
in vitro
(
S)-
equol production.
IMPORTANCE
(
S
)-equol ((
S
)-EQ) plays a crucial role in maintaining human health, along with its known capacity to prevent and treat various diseases, including cardiovascular diseases, metabolic syndromes, osteoporosis, diabetes, brain-related diseases, high blood pressure, hyperlipidemia, obesity, and inflammation. However, factors affecting individual variations in (
S
)-EQ production and the underlying regulatory mechanisms remain elusive. This study examines the association between functional genes and (
S
)-EQ production, highlighting a potential correlation between the DZNR gene and (
S
)-EQ content. Various types of DZNR may be linked to the regulation of (
S
)-EQ synthesis. Furthermore, the identification of a new DDRC gene offers promising prospects for enhancing in vitro (
S
)-EQ production.