156
7 Microbial Activities on Uranium
Adsorption of U compounds onto the bacterial cell surface is a natural phenomenon,
as it provides an efficient matrix for complexation of the element at low pH conditions; however, Acharya et al. (2009) pointed out that Synechococcus elongatus, a
marine cyanobacterium, has the capacity to bind of uranyl carbonate even at pH 7.8.
Sequestration of U is also observed in Anabaena torulosa, a marine, nitrogen- fixing
cyanobacterium, which can be removed from the bacteria through acidification
(Acharya et al. 2012; Acharya and Apte 2013). In general, bacterial cells provide
high surface to volume ratio and represent a number of polymers (like lipopolysaccharides, peptidoglycan, glycolipids and proteins) on their cell surface that act as
metal-binding ligands (Beazley et al. 2007; Acharya 2015). Bacteria show various
adaptive strategies to survive in the U mining fields. Working on U-tolerant soil
bacteria of Domiasiat deposit of U ore in Northeast India, scientists have pointed
out that phosphatase-positive phenotype was dominant (around 76%) with
Firmicutes (51%) and Gammaproteobacteria (26%) and is most dominant with
considerable amount of Actinobacteria (11%), Bacteroidetes (10%) and
Betaproteobacteria (2%) (Kumar et al. 2013a, b; Acharya 2015). Serratia marcescens and Burkholderia arboris are reported as potential species for U precipitation
and decontamination (Acharya 2015).
8 Accumulation of Uranium in Plants
Accumulation of U varies in different plant species. Researchers have cited various
toxic effects in different plant species. In tomato plants, Gulati et al. (1980) reported
a decrease in yield in soil U level from 1 to 6 mg kg
−1
. Sheppard et al. (1992)
reported higher biomass having soil U levels of 10,000 mg kg
−1
in Brassica rapa,
while other plants showed harmful effects above 300 mg kg
−1
U in soil. Entry et al.
(1996) reported higher accumulation (5000–10000 times higher) of U in sunflower
from contaminated aquatic ambience. Studying on phytoremediation with plant
Brassica juncea in organic-amended soil, researchers reported that accumulation of
U in shoot increased from 5 mg kg
−1
to more than 5000 mg kg
−1
(Huang et al. 1998;
ANRCP 1998). Dushenkov et al. (1997) reported that sunflower plants were having
potential to treat U-contaminated water, streams through the process of rhizofiltration, where bioaccumulation coefficients of U concentrations (roots: aqueous phase)
reached 30,000. Shtangeeva et al. (2006), working with natural plant species wheatgrass (Triticum repens L.) and plantain (Plantago major) on U and Th (thorium)
uptake after soil application, revealed that uptake was more efficient for U than for
Th. Further, it was observed in the study that soil microbiota at rhizosphere changed
significantly and chlorophyll content of the plants decreased (Shtangeeva et al.
2006). Stojanović et al. (2012) reported that Nicotiana tabacum L. (tobacco plant
with Virginia and Burley varieties) is a potential hyperaccumulator plant for U
D. K. Gupta et al.
7 Microbial Activities on Uranium
Adsorption of U compounds onto the bacterial cell surface is a natural phenomenon,
as it provides an efficient matrix for complexation of the element at low pH conditions; however, Acharya et al. (2009) pointed out that Synechococcus elongatus, a
marine cyanobacterium, has the capacity to bind of uranyl carbonate even at pH 7.8.
Sequestration of U is also observed in Anabaena torulosa, a marine, nitrogen- fixing
cyanobacterium, which can be removed from the bacteria through acidification
(Acharya et al. 2012; Acharya and Apte 2013). In general, bacterial cells provide
high surface to volume ratio and represent a number of polymers (like lipopolysaccharides, peptidoglycan, glycolipids and proteins) on their cell surface that act as
metal-binding ligands (Beazley et al. 2007; Acharya 2015). Bacteria show various
adaptive strategies to survive in the U mining fields. Working on U-tolerant soil
bacteria of Domiasiat deposit of U ore in Northeast India, scientists have pointed
out that phosphatase-positive phenotype was dominant (around 76%) with
Firmicutes (51%) and Gammaproteobacteria (26%) and is most dominant with
considerable amount of Actinobacteria (11%), Bacteroidetes (10%) and
Betaproteobacteria (2%) (Kumar et al. 2013a, b; Acharya 2015). Serratia marcescens and Burkholderia arboris are reported as potential species for U precipitation
and decontamination (Acharya 2015).
8 Accumulation of Uranium in Plants
Accumulation of U varies in different plant species. Researchers have cited various
toxic effects in different plant species. In tomato plants, Gulati et al. (1980) reported
a decrease in yield in soil U level from 1 to 6 mg kg
−1
. Sheppard et al. (1992)
reported higher biomass having soil U levels of 10,000 mg kg
−1
in Brassica rapa,
while other plants showed harmful effects above 300 mg kg
−1
U in soil. Entry et al.
(1996) reported higher accumulation (5000–10000 times higher) of U in sunflower
from contaminated aquatic ambience. Studying on phytoremediation with plant
Brassica juncea in organic-amended soil, researchers reported that accumulation of
U in shoot increased from 5 mg kg
−1
to more than 5000 mg kg
−1
(Huang et al. 1998;
ANRCP 1998). Dushenkov et al. (1997) reported that sunflower plants were having
potential to treat U-contaminated water, streams through the process of rhizofiltration, where bioaccumulation coefficients of U concentrations (roots: aqueous phase)
reached 30,000. Shtangeeva et al. (2006), working with natural plant species wheatgrass (Triticum repens L.) and plantain (Plantago major) on U and Th (thorium)
uptake after soil application, revealed that uptake was more efficient for U than for
Th. Further, it was observed in the study that soil microbiota at rhizosphere changed
significantly and chlorophyll content of the plants decreased (Shtangeeva et al.
2006). Stojanović et al. (2012) reported that Nicotiana tabacum L. (tobacco plant
with Virginia and Burley varieties) is a potential hyperaccumulator plant for U
D. K. Gupta et al.