ABSTRACT
Aggregating strains of
Tetragenococcus halophilus
tend to be trapped during soy sauce mash-pressing process and are, therefore, critical for clear soy sauce production. However, the precise molecular mechanism involved in
T. halophilus
aggregation remains elusive. In previous studies, we isolated a number of aggregating strains, including
T. halophilus
AB4 and AL1, and showed that a cell surface proteinaceous aggregation factor is responsible for their aggregation phenotype. In the present study, we explored the role of polysaccharide intercellular adhesin (PIA) in aggregate formation in
T. halophilus
SL10, isolated from soy sauce. SL10 exhibited similar aggregation to AB4 and AL1 but formed a non-uniform precipitate with distinctive wrinkles at the bottom of the test tube, unlike AB4 and AL1. Insertion sequence mutations in each gene of the
ica
operon diminished aggregation and PIA production, highlighting the critical role of IcaADBC-mediated PIA production in
T. halophilus
aggregation. Furthermore, two non-aggregating cardiolipin synthase (
cls
) gene mutants with intact
ica
operon did not produce detectable PIA. Phospholipid composition analysis in
cls
mutants revealed a decrease in cardiolipin and an increase in phosphatidylglycerol levels, highlighting the association between phospholipid composition and PIA production. These findings provide evidence for the pivotal role of
cls
in PIA-mediated aggregation and lay the foundation for future studies to understand the intricate networks of the multiple aggregation factors governing microbial aggregation.
IMPORTANCE
Aggregation, commonly observed in various microbes, triggers biofilm formation in pathogenic variants and plays a beneficial role in efficient food production in those used for food production. Here, we showed that
Tetragenococcus halophilus
, a microorganism used in soy sauce fermentation, forms aggregates in a polysaccharide intercellular adhesin (PIA)-mediated manner. Additionally, we unveiled the relationship between phospholipid composition and PIA production. This study provides evidence for the presence of aggregation factors in
T. halophilus
other than the proteinaceous aggregation factor and suggests that further understanding of the coordinated action of these factors may improve clarified soy sauce production.