Alkaline Anaerobic Respiration: Isolation and Characterization of a Novel Alkaliphilic and Metal-Reducing Bacterium

Abstract

Iron-reducing enrichments were obtained from leachate ponds at the U.S. Borax Company in Boron, Calif. Based on partial small-subunit (SSU) rRNA gene sequences (approximately 500 nucleotides), six isolates shared 98.9% nucleotide identity. As a representative, the isolate QYMF was selected for further analysis. QYMF could be grown with Fe(III)-citrate, Fe(III)-EDTA, Co(III)-EDTA, or Cr(VI) as electron acceptors, and yeast extract and lactate could serve as electron donors. Growth during iron reduction occurred over the pH range of 7.5 to 11.0 (optimum, pH 9.5), a sodium chloride range of 0 to 80 g/liter (optimum, 20 g/liter), and a temperature range of 4 to 45°C (optimum, approximately 35°C), and iron precipitates were formed. QYMF was a strict anaerobe that could be grown in the presence of borax, and the cells were straight rods that produced endospores. Sodium chloride and yeast extract stimulated growth. Phylogenetic analysis of the SSU rRNA gene indicated that the bacterium was a low-G؉C gram-positive microorganism and had 96 and 92% nucleotide identity with Alkaliphilus transvaalensis and Alkaliphilus crotonatoxidans, respectively. The major phospholipid fatty acids were 14:1, 16:17c, and 16:0, which were different from those of other alkaliphiles but similar to those of reported iron-reducing bacteria. The results demonstrated that the isolate might represent a novel metal-reducing alkaliphilic species. The name Alkaliphilus metalliredigens sp. nov. is proposed. The isolation and activity of metal-reducing bacteria from borax-contaminated leachate ponds suggest that bioremediation of metal-contaminated alkaline environments may be feasible and have implications for alkaline anaerobic respiration.Bacterial metal reduction has widened the realm of lifesupporting biological reactions (29) and has been implicated as an important biochemical process on early Earth (20,36,39). The ability to reduce metals can be exploited for the bioreduction or immobilization of many toxic metals, including cobalt, chromium, uranium, and technetium (6). However, metal reduction in alkaline environments has not been well documented.Concentrated deposits of boron exist in some arid regions (e.g., Turkey and the United States) and are economically exploited for products including fiberglass, ceramics, glass, laundry bleaches, fire retardants, insecticides, and semiconductors (25, 42). Borax is a common detergent ingredient and is sometimes used as a mild disinfectant. The toxicity is low, but boron is not completely harmless. Boron can potentially affect reproductive organs of males and impair fetal development in pregnant females, as well as be phytotoxic (27,30). In addition, sodium perborate has been shown to be an in vitro mutagen (34).Metal-reducing bacteria can be isolated from a variety of habitats, and much work has focused on the metal-reducing bacteria Shewanella oneidensis (28) and Geobacter spp. (22). Sites contaminated with toxic metals can have drastically different environmental conditions, and the biological reduc...

Biogeochemical Reduction Processes in a Hyper-Alkaline Leachate Affected Soil Profile

“…Alkaliphiles are commonly divided into two broad groups; those that grow from circum-neutral to alkaline conditions are classified as facultative alkaliphiles (Sturr et al 1994), however, those that only growth at around pH 9 or above are classified as obligate alkaliphiles (McMillan et al 2009). Although for all alkaliphiles optimum growth commonly occurs at around pH 9-10, some species are reported to continue to grow up to around pH 12.5 (Takai et al 2001;Ye et al 2004;Pollock et al 2007). Another important consideration in alkaline environments is the nature of the organic matter (electron donors) present in affected soils.…”

“…Some are entirely natural, e.g., soda lakes, hot springs, oceanographic cold seeps, deep mine waters (Takai et al 2001;Takai et al 2005;Pollock et al 2007;McMillan et al 2009;Brazelton et al 2010), but many are also due to human activities. These anthropogenic sites occur as a result of the presence of residues from a range of industrial processes, e.g., lime production waste, steelworks slags, coal combustion residues, Solvay process waste, chromite ore processing residues, bauxite processing wastes, borax wastes and cementitious construction wastes (Effler et al 1991;Carlson and Adriano 1993;Townsend et al 1999;Deakin et al 2001;Ye et al 2004;Mayes et al 2006;Mayes et al 2008;Hartland et al 2009;Mayes et al 2011). Weathering of these wastes typically produces highly alkaline leachate (pH 10-13) due to the ubiquitous presence of Ca, Na and K oxides (primarily CaO) that hydrolyze in natural waters to produce soluble metal hydroxides.…”

Aerobic bioreduction of nickel(II) to elemental nickel with concomitant biomineralization

“…Alkaliphilus crotonatoxidans (Cao et al 2003) and Alkaliphilus metalliredigens sp. nov. (Ye et al 2004) could grow from pH 5.5 to 9.0 with an optimum pH of 7.5, and from pH 7.5 to 11.0 with an optimum pH of 9.5, respectively. However, these strains cannot grow under aerobic conditions.…”

Bacterial Diversity in the Hyperalkaline Allas Springs (Cyprus), a Natural Analogue for Cementitious Radioactive Waste Repository

“…To date, alkaline metal reduction by pure cultures has been reported (at least for Fe(III) reduction) for Anaerobranca californiensis (Gorlenko et al 2004), Alkaliphilus metalliredigens (Ye et al 2004), Alkaliphilus metalliredigens QYMF (Roh et al 2007), Alkaliphilus peptidofermentans Z-7036 (Zhilina et al 2009a), Natronincola ferrireducens and Natronincola peptidovorans (Zhilina et al 2009b), Bacillus sp. strain SFB (Pollock et al 2007), Bacillus pseudofirmus MC02 (Ma et al 2012), and a Serratia sp.…”

“…Enrichment cultures were set up anaerobically by supplementing each of samples Cyp1, Cyp2, Cyp3, Cyp4, Cyp5 with an equal volume of a ferric-citrate containing medium that was largely based on a medium that has been used previously to isolate metal-reducing alkaliphilic bacteria (Ye et al 2004). The medium used in this study contained 9.4 mM NH 4 Cl, 4.3 mM K 2 HPO 4 , 4 mM NaHCO 3 , 6.1 mM Na 2 SeO 4 , 17.1 mM NaCl, 10 ml L ¡1 mineral stock solution (Lovley et al 1984), 7 mM sodium lactate, 7 mM sodium acetate, 0.025 g L ¡1 yeast extract, and 15 mM Fe(III)-citrate.…”