Isolation of Iodide-Oxidizing Bacteria from Iodide-Rich Natural Gas Brines and Seawaters

Abstract

Iodide-oxidizing bacteria (IOB), which oxidize iodide (I-) to molecular iodine (I2), were isolated from iodide-rich (63 microM to 1.2 mM) natural gas brine waters collected from several locations. Agar media containing iodide and starch were prepared, and brine waters were spread directly on the media. The IOB, which appeared as purple colonies, were obtained from 28 of the 44 brine waters. The population sizes of IOB in the brines were 10(2) to 10(5) colony-forming units (CFU) mL(-1). However, IOB were not detected in natural seawaters and terrestrial soils (fewer than 10 CFU mL(-1) and 10(2) CFU g wet weight of soils(-1), respectively). Interestingly, after the enrichment with 1 mM iodide, IOB were found in 6 of the 8 seawaters with population sizes of 10(3) to 10(5) CFU mL(-1). 16S rDNA sequencing and phylogenetic analyses showed that the IOB strains are divided into two groups within the alpha-subclass of the Proteobacteria. One of the groups was phylogenetically most closely related to Roseovarius tolerans with sequence similarities between 94% and 98%. The other group was most closely related to Rhodothalassium salexigens, although the sequence similarities were relatively low (89% to 91%). The iodide-oxidizing reaction by IOB was mediated by an extracellular enzyme protein that requires oxygen. Radiotracer experiments showed that IOB produce not only I2 but also volatile organic iodine, which were identified as diiodomethane (CH2I2) and chloroiodomethane (CH2ClI). These results indicate that at least two types of IOB are distributed in the environment, and that they are preferentially isolated in environments in which iodide levels are very high. It is possible that IOB oxidize iodide in the natural environment, and they could significantly contribute to the biogeochemical cycling of iodine.

Halocarbon emissions and sources in the equatorial Atlantic Cold Tongue

“…4, 5) could indicate similar production and sink processes at depth. Bacterial formation of CH 2 I 2 (Fuse et al, 2003;Amachi et al, 2005) in the upper thermocline could also be an additional source for this compound. Alternatively, CH 2 I 2 may not degrade as quickly as CHBr 3 and CH 3 I in greater depths, which would lead to its accumulation below the mixed layer.…”

Transformation of iodate to iodide in marine phytoplankton driven by cell senescence

“…A review of the literature on this subject reveals only one reference to a chloroperoxidase in the fungus Caldariomyces fumago that can oxidise iodide to iodate (Thomas & Hager 1968). Iodoperoxidases are also present in marine bacteria (Gozlan & Margalith 1973, 1974, Amachi et al 2005, though none of these studies found oxidation through to iodate. Another possibility would be that iodide had been incorporated into the phytoplankton cells, or lost as I 2 .…”

Microbial Contribution to Global Iodine Cycling: Volatilization, Accumulation, Reduction, Oxidation, and Sorption of Iodine

“…However, "P. iodooxidans" has not been deposited in any culture collections and is no longer available. Recently, Fuse et al 33) and Amachi et al 8) individually isolated iodide-oxidizing bacteria from marine environmental samples. Phylogenetic analyses showed that iodideoxidizing bacteria could be divided into two groups within the α-subclass of Proteobacteria.…”