Microdistribution of sulfate‐reducing bacteria in sediments of a hypertrophic lake and their response to the addition of organic matter

Abstract

AbstractTo clarify the ecological significance of the association of sulfate‐reducing bacteria (SRB) with sediment particle size, SRB utilizing lactate (l‐SRB), propionate (p‐SRB) and acetate (a‐SRB) were examined with different sizes of sediment particles in a hypertrophic freshwater lake using the anaerobic plate count method. The numbers of l‐SRB and a‐SRB were 104–105 colony forming units (CFU) per ml in the 0–3 cm layer and 102–103 CFU ml−1 in the 10–13 cm layer while the numbers of p‐SRB were one or two orders lower than those of l‐SRB and a‐SRB. A sediment suspension was fractionated into four fractions (<1, 1–10, 10–94 and >94 μm). The highest proportions of l‐SRB and a‐SRB were found in the 10–94 μm fraction: 66–97% for l‐SRB and 53–98% for a‐SRB. The highest proportion of p‐SRB was found in the >94 μm fraction (70–74%). These results indicate that most SRB were associated with sediment particles. One isolate from an acetate‐utilizing enrichment culture was similar to Desulfotomaculum acetoxidans, a spore‐forming sulfate‐reducing bacterium. When lactate and sulfate were added to sediment samples, l‐SRB and a‐SRB in the <10 μm‐fraction grew more rapidly than those in whole sediment for the first 2 days. This result suggests that nutrients uptake by free‐living and small particle‐associated (<10 μm) SRB is higher than that by SRB associated with larger particles.