Abstract

Anaerobic sulfate-reducing bacteria (SRB) have been encapsulated in a hydrous, alcohol-free, silica matrix produced by acidifying an aqueous mixture of colloidal silica and an SRB culture. The viability of the encapsulated species was investigated by monitoring the formation of the metabolic products, H₂S and acetate. Freshly prepared gel samples containing ∼5 × 10⁵ cells cm⁻³ of gel reduced sulfate ions at a rate of ∼11 µg h⁻¹ cm⁻³ gel, when placed in a nutrient solution based on Postgate's Medium C. Less than 0.1% of the encapsulated species were leached into the nutrient solution over a 10 day period. Gels drained of nutrient solution and stored under nitrogen for 10 weeks at ambient temperature initially exhibited low sulfate reduction rates (∼2 µg h⁻¹ cm⁻³ gel) on re-immersion in nutrient, presumably due to a decrease in the encapsulated cell population. However, the initial sulfate reduction rate of ∼11 µg h⁻¹ cm⁻³ of gel was re-established after soaking the gel samples in nutrient solution for six days, indicating that the encapsulated bacterial population could be rapidly restored within the gel's pore network, even after several months of storage.