113
pathogenic yeast, Candida albicans. It was hypothesized that the toxicity of
nanoparticle depends on solubilization of zinc from zinc oxide nanoparticles in
the medium.
Zinc oxide nanoparticles also showed toxicity to various algal species such as
Skeletonema marioni, Thalassiosira pseudonana, Dunaliella tertiolecta, and
Isochrysis galbana at 1 ppm concentration. Miller et al. (2010) measured 50–75%
decrease in growth rate of these algae by 20–30 nm sized ZnO nanoparticles at
1 ppm concentration. Similarly, it showed toxicity to microalgae Pseudokirchneriella
subcapitata, diatom Thalassiosira pseudonana, and cyanobacteria Anabaena flosaquae (Franklin et al. 2007; Miao et al. 2010; Brayner et al. 2010).
4.5.6 Iron Nanoparticles
Iron is also an important micronutrient for plant growth promotion and microbial
metabolism. The high concentration of iron in the soil directly impacted the physiology of plant and microbial community and disorganized the soil ecosystem by
transforming microbial community structure. He et al. (2011) found that Fe 2 O 3
nanoparticles induced the invertase and urease activity at 420–1260 ppm but bacterial biomass did not change. Similarly, Cullen et al. (2011) reported that at 10 ppm
concentration zero valent iron nanoparticles affected microbial enzymatic activity
by stimulation of dehydrogenase activity, inhibition of microbial ammonia oxidation, and no impact on hydrolase activity.
4.5.7 Silicon and Aluminum Oxide Nanoparticles
The effect of silicon dioxide and aluminum oxide nanoparticles on microbial community is very rare. Recently, McGee et al. (2017) reported that silicon oxide and
aluminum oxide nanoparticles did not alter the soil ureases, dehydrogenase activity
and soil microbial community but silver nanoparticles reduced that enzyme activity
significantly. On the exposure of silver nanoparticles, abundance of Proteobacteria
increased but Acidobacteria and Verrucomicrobia decreased.
4.5.8 Nano-Ceria (CeO 2 )
Microbial activity related to carbon, nitrogen, and phosphorus cycle is affected by
the presence of nano-ceria (Hamidat et al. 2016). Authors used different sized (3.5
or 31 nm) citrate-coated ceria nanoparticles to evaluate their activity in rhizospheric
soil at 1 mg.kg
−1
concentration. They found decrease in microbial enzymatic activity and alteration in bacterial community structure. Citrate coating on nano-ceria
4 Nano-toxicity to Microbes: Potential Implications of Nanomaterials on Microbial…
pathogenic yeast, Candida albicans. It was hypothesized that the toxicity of
nanoparticle depends on solubilization of zinc from zinc oxide nanoparticles in
the medium.
Zinc oxide nanoparticles also showed toxicity to various algal species such as
Skeletonema marioni, Thalassiosira pseudonana, Dunaliella tertiolecta, and
Isochrysis galbana at 1 ppm concentration. Miller et al. (2010) measured 50–75%
decrease in growth rate of these algae by 20–30 nm sized ZnO nanoparticles at
1 ppm concentration. Similarly, it showed toxicity to microalgae Pseudokirchneriella
subcapitata, diatom Thalassiosira pseudonana, and cyanobacteria Anabaena flosaquae (Franklin et al. 2007; Miao et al. 2010; Brayner et al. 2010).
4.5.6 Iron Nanoparticles
Iron is also an important micronutrient for plant growth promotion and microbial
metabolism. The high concentration of iron in the soil directly impacted the physiology of plant and microbial community and disorganized the soil ecosystem by
transforming microbial community structure. He et al. (2011) found that Fe 2 O 3
nanoparticles induced the invertase and urease activity at 420–1260 ppm but bacterial biomass did not change. Similarly, Cullen et al. (2011) reported that at 10 ppm
concentration zero valent iron nanoparticles affected microbial enzymatic activity
by stimulation of dehydrogenase activity, inhibition of microbial ammonia oxidation, and no impact on hydrolase activity.
4.5.7 Silicon and Aluminum Oxide Nanoparticles
The effect of silicon dioxide and aluminum oxide nanoparticles on microbial community is very rare. Recently, McGee et al. (2017) reported that silicon oxide and
aluminum oxide nanoparticles did not alter the soil ureases, dehydrogenase activity
and soil microbial community but silver nanoparticles reduced that enzyme activity
significantly. On the exposure of silver nanoparticles, abundance of Proteobacteria
increased but Acidobacteria and Verrucomicrobia decreased.
4.5.8 Nano-Ceria (CeO 2 )
Microbial activity related to carbon, nitrogen, and phosphorus cycle is affected by
the presence of nano-ceria (Hamidat et al. 2016). Authors used different sized (3.5
or 31 nm) citrate-coated ceria nanoparticles to evaluate their activity in rhizospheric
soil at 1 mg.kg
−1
concentration. They found decrease in microbial enzymatic activity and alteration in bacterial community structure. Citrate coating on nano-ceria
4 Nano-toxicity to Microbes: Potential Implications of Nanomaterials on Microbial…