A strain KSUCr3 with extremely high Cr(VI)-reducing ability under
alkaline conditions was isolated from hypersaline soda lakes and
identified as Amphibacillus sp. on the basis of 16S rRNA gene sequence
analysis. The results showed that Amphibacillus sp. strain KSUCr3 was
tolerance to very high Cr(VI) concentration (75 mM) in addition to high
tolerance to other heavy metals including Ni2+ (100 mM), Mo2+ (75 mM),
Co2+ (5 mM), Mn2+ (100 mM), Zn2+ (2 mM), Cu2+ (2 mM) and Pb (75 mM).
Strain KSUCr3 was shown to be of a high efficiency in detoxifying
chromate, as it could rapidly reduce 5 mM of Cr(VI) to a non detectable
level over 24 hrs. In addition, strain KSUCr3 could reduce Cr(VI)
efficiently over a wide range of initial Cr(VI) concentrations (1-10
mM) in alkaline medium under aerobic conditions without significant
effect on the bacterial growth. Addition of glucose, NaCl and Na2CO3 to
the culture medium caused a dramatic increase in Cr(VI)-reduction by
Amphibacillus sp. strain KSUCr3. The maximum chromate removal was
exhibited in alkaline medium containing 1.5% Na2CO3, 0.8% glucose, and
1.2% NaCl, at incubation temperature of 40\ub0C and shaking of 100
rpm. Under optimum Cr(VI) reduction conditions, Cr(VI) reduction rate
reached 237 \u3bcMh1 which is one of the highest Cr(VI) reduction
rate, under alkaline conditions and high salt concentration, compared
to other microorganisms that has been reported so far. Furthermore, the
presence of other metals, such as Ni2+, Co2+, Cu2+ and Mn2+ slightly
stimulated Cr(VI)-reduction ability by the strain KSUCr3.The isolate,
Amphibacillus sp. strain KSUCr3, exhibited an ability to repeatedly
reduce hexavalent chromium without any amendment of nutrients,
suggesting its potential application in continuous bioremediation of
Cr(VI). The results also revealed the possible isolation of potent
heavy metals resistant bacteria from extreme environment such as
hypersaline soda lakes