Microbial communities in hydrothermal vent sediments change in response to shifts in pH and redox potential. Sediment samples from different vents were studied in microcosm experiments for 90 days. The most acidified site showed a diverse microbial community with species like Thermotoga and Desulfobacterota. Spore-forming species increased in all conditions, and proteolytic activity was boosted while alkaline phosphatase activity decreased at low pH. The study confirmed that microbial communities react differently based on their initial environment.