Encapsulation of sulfate-reducing bacteria in a silica host

Anaerobic sulfate-reducing bacteria (SRB) have been encapsulated in a hydro us, alcohol-free, silica matrix produced by acidifying an aqueous mixture o f colloidal silica and an SRB culture. The viability of the encapsulated sp ecies was investigated by monitoring the formation of the metabolic product s, H2S and acetate. Freshly prepared gel samples containing similar to 5 x 10(5) cells cm(-3) of gel reduced sulfate ions at a rate of similar to 11 m u g 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 th e nutrient solution over a 10 day period. Gels drained of nutrient solution and stored under nitrogen for 10 weeks at ambient temperature initially ex hibited low sulfate reduction rates (similar to 2 mu g 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 similar to 11 mu g h(-1) cm(-3) of gel was re-established after soaking the gel sampl es in nutrient solution for six days, indicating that the encapsulated bact erial population could be rapidly restored within the gel's pore network, e ven after several months of storage.