U (VI) tolerance affects Shewanella sp. RCRI7 biological responses: growth, morphology and bioreduction ability

Mahsa Zarei,Faezeh Fatemi,Razieh Ghasemi,Mohammad Mir-Derikvand,Touran Rabiee Samani,Hamzeh Hosseinpour

doi:10.1007/s00203-021-02716-6

Abstract

Native Shewanella sp. RCRI7 is recently counted as an operative bacterium in the uranium bio-reduction. The aim of this study was to investigate the effects of uranium tolerance on the morphology and population of RCRI7, following its potential removal capacity in different time intervals. In this research, the bacterial growth and uranium removal kinetic were evaluated in aerobic TSB medium, uranium-reducing condition (URC), aerobic uranium-containing (AUC) and anaerobic uranium-free (AUF) solution, following evaluations of omcAB gene expressions. In addition, spectrophotometry analyses were performed in URC confirming the bio-reduction mechanism. It was found that the bacteria can grow efficiently in the presence of 0.5mM uranium anaerobically, unlike AUC and AUF solutions. Since the bacterium's adsorption capacity is quickly saturated, it can be deduced that uranium reduction should be dominant as incubation times proceed up to 84h in URC. In 92h incubation, the adsorbed uranium containing unreduced and reduced (U (IV) monomeric), was released to the solution due to either increased pH or bacterial death. In AUC and AUF, improper conditions lead to the reduced bacterial size (coccus-shape formation) and increased bacterial aggregations; however, membrane vesicles produced by the bacteria avoid the uranium incrustation in AUC. In overall, this study implies that Shewanella sp. RCRI7 are well tolerated by uranium under anaerobic conditions and the amount of regenerated uranium increases over time in the reduced form.

Highlights

Bacteria have the ability to carry out reduction, oxidation, adsorption on cell surface groups, and precipitation of radionuclides by interacting with ligands such as phosphate (Lloyd and Renshaw 2005; Icenhower et al 2010; Newsome et al 2014)
Shewanella RCRI7 is the Iranian native strain isolated and identified in 2011 from Qurugöl Lake near to the city of Tabriz by Dr Tarhriz. Identification of this bacterium and determination of its phylogenetic tree based on 16s rRNA sequence indicated that this strain is very similar to known strains such as Shewanella putrefaciens and Shewanella xiamenensis, but most of all it is similar to the Shewanella oneidensis MR-1 Strain, a model bacteria in the uranium bioreduction (Tarhriz et al 2011)
It can be deduced that RCRI7 is capable of using uranium as an electron acceptor under anaerobic condition (URC) where uranium proper amount can be associated with the cell growth

Summary

Introduction

Bacteria have the ability to carry out reduction, oxidation, adsorption on cell surface groups, and precipitation of radionuclides by interacting with ligands such as phosphate (Lloyd and Renshaw 2005; Icenhower et al 2010; Newsome et al 2014). The selected Shewanella genus is aquatic gram-negative rod-shaped bacteria belongs to the Shewanellaceae family (facultative anaerobic gammaprotobacteria) grown in different environments. These gram-negative bacteria are able to use various organic and inorganic substances, including metals, as electron acceptors in their respiratory pathway which reduce them due to their large number of cytochromes and multiple electron transfer pathways (Pinchuk et al 2010; Wang et al 2010; Saffarini et al 2015). Shewanella RCRI7 is the Iranian native strain isolated and identified in 2011 from Qurugöl Lake near to the city of Tabriz by Dr Tarhriz. Identification of this bacterium and determination of its phylogenetic tree based on 16s rRNA sequence indicated that this strain is very similar to known strains such as Shewanella putrefaciens and Shewanella xiamenensis, but most of all it is similar to the Shewanella oneidensis MR-1 Strain, a model bacteria in the uranium bioreduction (Tarhriz et al 2011)

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