Genomic insights into salt-tolerant, exopolysaccharide-producing Bacillus velezensis DTA1 isolated from coral island soil in Vietnam: Implications for soil remediation

Bacillus velezensis ( B. velezensis ) is widely recognised for its remarkable ability to tolerate environmental stresses, partly through the production of exopolysaccharides (EPS), which enhance survival via biofilm formation. In this study, we characterised a salt-tolerant, EPS-producing strain, B. velezensis DTA1, isolated from a coral island in Vietnam. This strain exhibited significant tolerance to salinity and various heavy metals, including cadmium, mercury, chromium, arsenic, lead, zinc and cobalt. EPS production increased significantly under salt stress. Whole genome sequencing analysis revealed several genes encoding phosphotransferase system transport proteins and enzymes that facilitate the conversion of various carbon sources into corresponding nucleotide sugars in the DTA1. The eps and levan biosynthetic gene clusters related to EPS biosynthetic pathways were detected in the DTA1 genome explaining its ability to produce EPS. Furthermore, the EPS yield and structural composition of this strain are strongly governed by the sugar source used. The study strain also harbours multiple genes related to osmotic stress, heavy metal stress and oxidative stress. Unlike previous studies focusing solely on EPS yield or biological activity, this work provides an integrated view of the genetic, biochemical and environmental factors governing EPS biosynthesis and stress tolerance in B. velezensis DTA1. This study provides the first insight into the genetic potential and biochemical traits of a B. velezensis strain adapted to the extreme conditions of an offshore coral island. Our findings not only deepen the understanding of this strain’s stress adaptation mechanisms, but also reveal its unique EPS biosynthetic potential via two distinct pathways, the epsA–O operon and levan synthesis, which have not previously been reported together in B. velezensis . Furthermore, this study expands the potential application of indigenous halophilic bacteria to improve arid, saline coral sand and coastal soils, especially in the context of Vietnam, which is experiencing the escalating impacts of climate change that are expanding the area of saline soils and threatening the sustainability of agriculture.