Tolerance and immobilization of cobalt by some bacteria from ferromanganese crusts of the afanasiy Nikitin Seamounts
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Bacteria isolated from cobalt–enriched ferromanganese crusts on the Afanasiy Nikitin Seamounts in the Equatorial Indian Ocean were examined for their ability to tolerate, and immobilize cobalt in unamended seawater and seawater amended with 0.01% glucose. Retrievable bacterial counts in the form of CFU (colony forming units) on media supplemented with 1 mmol Co 1sup(-1) (58 mg Co 1sup(-1)) and 1 mmol Mn 1sup(-1) (54 mg Mn 1sup(-1) ) were in the range of 1.71 × 10 sup(4) to 1.05 × 10 sup(5) gm sup(-1) (wet wt) of crust, respectively. Most of the isolates (14/24) were pigmented and showed taxonomic affinities to Flavobacterium sp. Two representative isolates were tested for their tolerance of cobalt. It is observed that in amended medium, the isolates tolerated up to 1 mmol Co 1sup(-1), whereas in unamended medium they tolerated upto 10 mmol Co 1sup(-1). Microscopic observations of cultures incubated with 10 mmol Co 1sup(-1) showed the occurrence of an extracellular slime layer, which may be responsible for immobilizing the cobalt from the liquid phase. In the unamended medium, the tolerance and stimulation in total cell counts was similar to that in amended medium or sometimes greater. Total cell counts peaked at 100 Mu mol Co 1sup(-1) for incubations in unamended medium (1.1–2.5 × 10 sup(11) cells 1sup(-1)) and at 0.1–1 Mu mol Co 1sup(-1) for incubations in amended medium (1.5–2.6 × 10 sup(11) cells 1sup(-1)). Counts of formazan-stained respiring cells of both the isolates in the unamended medium reached up to a maximum of 2.9–7.8 × 10 sup(10) 1sup(-1) after incubation for 10 days at 23(plus or minus 1) degrees C. In the amended medium cell counts of respiring cells attained a maximum in the range of 4.6–15.8 × 10 sup(10) 1sup(-1) at 100 Mu mol Co 1sup(-1). The Co immobilization rate was on average 82 (plus or minus 87.9, n=24) Mu mol of Co d sup(-1). Since the isolates were naturally occurring bacteria from crusts, they could be more environmentally acceptable and safe if used for metal recovery and bio-bleaching.
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