Aluminum is the most abundant metal in the Earth's crust,
but it is usually bound in insoluble oxides and silicates (Macdonald and Martin,
Environmental acidification can increase levels of soluble
aluminum (Al(III)), which is of concern as Al(III) is known
to be toxic to many organisms (Williams, 1999).
No biological role has been identified for aluminum, but aluminum can replace hydrogen with limited efficiency
as an electron donor for methane production by methanogenic archaea (Belay and
Daniels, 1990). Research into microbial interactions
with aluminum has focused on corrosion of aluminum alloys, leaching of aluminum
from materials, and aluminum accumulation, toxicity and detoxification.
Organic and inorganic acids produced by bacteria and fungi can mobilize aluminum from a variety of materials. Corrosion of
aluminum alloys due to the growth of microorganisms was observed in aircraft fuel tanks in the 1960's (reviewed by Iverson, 1987), and remains a current
area of research (Yang et al, 1998).
Researchers have documented microbially-mediated aluminum leaching from the mineral spodumene (Karavaiko et al, 1980), red
mud waste remaining after the alkaline extraction of alumina from bauxite ores (Vachon et al, 1994),
incinerator fly ash
(Brombacher et al, 1998), and electronic scrap (Brandl et al, 2000).
Phosphate has been shown to influence the mechanisms of aluminum tolerance in Pseudomonas fluorescens grown with
aluminum-complexed citrate as a sole carbon source. In a phosphate-rich medium, P. fluorescens deposited aluminum in an insoluble extracellular
composed partly of phosphatidylethanolamine (Appanna and St. Pierre, 1996). When phosphate was limiting, aluminum was found
complexed with soluble extracellular metabolites (Appanna and St. Pierre, 1994). Iron concentration can determine which
aluminum detoxification mechanism is used by P. fluorescens (Appanna and Hamel, 1996). Cellular phosphate concentration can also modulate aluminum toxicity in Bradyrhizobium
japonicum (Mukherjee and Asanuma, 1998).
Aluminum binding and accumulation has been described in a variety of microorganisms. Isolated cell walls of Staphylococcus aureus were found
to bind aluminum ions (Bradley
and Parker, 1968), and Anabaena
cylindrica was found to accumulate aluminum in phosphate granules in the cell wall (Pettersson et al, 1985). Cell surface and
intracellular aluminum accumulation was observed in Eschericia coli (Guida et al, 1991). Aluminum uptake via hydroxamate siderophores can occur in the absence of iron in Bacillus megaterium (Hu and Boyer, 1996).
For more information:
Medline for aluminum metabolism AND bacteria
Appanna VD, St. Pierre M. Influence of phosphate on aluminum tolerance in Pseudomonas fluorescens. FEMS Microbiol Lett.
Appanna VD, St. Pierre M. Aluminum elicits exocellular phosphatidylethanolamine production in Pseudomonas
fluorescens. Appl Environ Microbiol. 1996 Aug;62(80):2778-82.
Brandl H, Bosshard R, Wegmann M. Computer-munching microbes: metal leaching from electronic scrap by bacteria and fungi.
Hydrometallurgy. 2001 Feb;59(3):319-26.
Brombacher C, Bachofen R, Brandl H. Development of a laboratory-scale leaching plant for metal extraction from fly ash by
Thiobacillus strains. Appl Environ Microbiol. 1998 Apr;64(4):1237-41.
Flis SE, Glenn AR, Dilworth MJ. The interaction between aluminium and root nodule bacteria. Soil Biol Biochem. 1993 Apr;25(1):403-17.
Hu X, Boyer GL. Siderophore-mediated aluminum uptake by Bacillus megaterium ATCC 19213. Appl Environ Microbiol.
Iverson WP. Microbial corrosion of metals. Adv Appl Microbiol.
Mukherjee SK, Asanuma S. Possible role of cellular phosphate pool and subsequent accumulation of inorganic phosphate on
the aluminum tolerance in Bradyrhizobium japonicum. Soil Biol Biochem. 1998 Oct;30(12):1511-16.
Pettersson A, Kunst L, Bergman B, Roomans GM. Accumulation of aluminium by Anabaena cylindrica into polyphosphate granules and
cell walls: an X-ray energy-dispersive microanalysis study. J Gen Microbiol. 1985;131:2545-48.
Rogers NJ, Carson KC, Glenn AR, Dilworth MJ, Hughes MN, Poole
RK. Alleviation of aluminum toxicity to Rhizobium leguminosarum
bv. viciae by the hydroxamate siderophore vicibactin. Biometals.
Vachon P, Rajeshwar DT, Auclair J-C, Wilkinson KJ. Chemical and biological leaching of aluminum from red mud. Environ Sci Technol. 1994;28(1):26-30.