Isolation and identification of manganese-reducing bacteria and estimates of microbial Mn(IV)-reducing potential in the Black Sea

Abstract

During the summer of 1988, profiles of major and minor nutrients in the western and central basins of the Black Sea showed a pronounced suboxic zone in which could be seen distinct zones of nitrate, manganese and iron reduction. Enrichment culture techniques, used to determine relative levels of microbial Mn(IV) and Fe(III) reduction potential, indicated very high levels of iron-reducing potential throughout the suboxic zone, and high levels of Mn(IV)-reducing potential in both the nitrate reduction (55 m) and the Mn(IV) reduction (85 m) zones. Bacteria were also directly isolated from various depths in the water column and tested for their ability to reduce Mn(IV). Using these direct techniques, the major group of organisms isolated from the 80–90 m (Mn reduction) zone were in the genus Shewanella, accounting for up to 20–50% of the total bacterial viable counts, and up to 1–5 × 10 5 bacteria per ml. At other depths, there were fewer Mn(IV)-reducing bacteria, and those that were found were in different taxonomic groups, including Pseudomonas spp., Bacillus spp., and some unidentified Gram-negative rods and coccobacilli. All of these bacteria were respiratory bacteria, and many were capable of both Fe(III) and Mn(IV) reduction.