Abstract
Arsenic (As) is a well-known toxic metalloid found naturally and released by different industries, especially in developing countries. Purple nonsulfur bacteria (PNSB) are known for wastewater treatment and plant growth promoting abilities. As-resistant PNSB were isolated from a fish pond. Based on As-resistance and plant growth promoting attributes, 2 isolates CS2 and SS5 were selected and identified as Rhodopseudomonas palustris and Rhodopseudomonas faecalis, respectively, through 16S rRNA gene sequencing. Maximum As(V) resistance shown by R. faecalis SS5 and R. palustris CS2 was up to 150 and 100 mM, respectively. R. palustris CS2 showed highest As(V) reduction up to 62.9% (6.29 ± 0.24 mM), while R. faecalis SS5 showed maximum As(III) oxidation up to 96% (4.8 ± 0.32 mM), respectively. Highest auxin production was observed by R. palustris CS2 and R. faecalis SS, up to 77.18 ± 3.7 and 76.67 ± 2.8 μg mL−1, respectively. Effects of these PNSB were tested on the growth of Vigna mungo plants. A statistically significant increase in growth was observed in plants inoculated with isolates compared to uninoculated plants, both in presence and in absence of As. R. palustris CS2 treated plants showed 17% (28.1 ± 0.87 cm) increase in shoot length and 21.7% (7.07 ± 0.42 cm) increase in root length, whereas R. faecalis SS5 treated plants showed 12.8% (27.09 ± 0.81 cm) increase in shoot length and 18.8% (6.9 ± 0.34 cm) increase in root length as compared to the control plants. In presence of As, R. palustris CS2 increased shoot length up to 26.3% (21.0 ± 1.1 cm), while root length increased up to 31.3% (5.3 ± 0.4 cm), whereas R. faecalis SS5 inoculated plants showed 25% (20.7 ± 1.4 cm) increase in shoot length and 33.3% (5.4 ± 0.65 cm) increase in root length as compared to the control plants. Bacteria with such diverse abilities could be ideal for plant growth promotion in As-contaminated sites.
Highlights
Arsenic (As) is a ubiquitous toxic metalloid which is released from several industrial processes such as mining, tanning of hides, and combustion of coal
Resistance against As(V) and plant growth promoting activities, such as auxin and Hydrogen Cyanide (HCN) production, were the main parameters used for the screening and selection of Purple nonsulfur bacteria (PNSB)
The isolates showing best results were identified as R. palustris CS2 and R. faecalis SS5 by aligning their 16S rRNA gene sequences with the NCBI nucleotide database using BLAST tool
Summary
Arsenic (As) is a ubiquitous toxic metalloid which is released from several industrial processes such as mining, tanning of hides, and combustion of coal. Due to these reasons, the level of As in drinking waters of many areas has been increased beyond WHO standard drinking water limits (0.01 mg L−1) [1]. As is primarily found in two major forms: arsenate [As(V)] and arsenite [As(III)] [2]. The toxicity of As causes reduced growth and low yields [7]. Given the possible complexity and severity of the BioMed Research International
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