Inorganic Carbon Modulates Emulsification Activity and Transcriptional Responses in Vreelandella zhaodongensis BS253

Inorganic carbon availability is an underexplored factor influencing extracellular emulsification-associated responses in haloalkaliphilic bacteria. Here, we show that Vreelandella zhaodongensis BS253 exhibits distinct physiological and transcriptional responses to CO2 enrichment and bicarbonate supplementation, accompanied by condition-dependent changes in emulsification activity. Both moderate CO2 enrichment (5–10%) and NaHCO3 supported high emulsification values (E24 > 60%). However, CO2 favored higher emulsification activity relative to biomass, whereas NaHCO3 promoted greater biomass accumulation and elevated absolute activity. Transcriptomic profiling revealed extensive condition-dependent reprogramming, particularly involving membrane transport, envelope-associated functions, and genes annotated as related to exopolysaccharide biosynthesis. Integrative phenotype-guided analyses prioritized candidate genes statistically associated with the emulsification phenotype. The extracellular emulsification-active material remained active across a broad range of salinity, temperature, pH, and pressure, demonstrating pronounced physicochemical robustness. Together, these findings indicate that inorganic carbon availability modulates emulsification activity and associated transcriptional responses in a haloalkaliphile and highlight extremophilic bacteria as promising platforms for sustainable bioprocesses based on inorganic carbon inputs.