Complexation and conformation of lead ion with poly-γ-glutamic acid in soluble state

Lingling Wang; Yamin Liu; Xiulin Shu; Shunying Lu; Xiaobao Xie; Qingshan Shi

doi:10.1371/journal.pone.0218742

Complexation and conformation of lead ion with poly-γ-glutamic acid in soluble state

PLoS One. 2019 Sep 13;14(9):e0218742. doi: 10.1371/journal.pone.0218742. eCollection 2019.

Authors

Lingling Wang¹, Yamin Liu¹, Xiulin Shu¹, Shunying Lu¹, Xiaobao Xie¹, Qingshan Shi¹

Affiliation

¹ State Key Laboratory of Applied Microbiology Southern China, Guangdong Provincial Key Laboratory of Microbial Culture Collection and Application, Guangdong Open Laboratory of Applied Microbiology, Guangdong Institute of Microbiology, Guangzhou, China.

Abstract

Complexation of microbial polymer in soluble state could impact the solubility, mobility, and bioavailability of heavy metals in the environment. The complexation of a bacterial exopolymer, poly-γ-glutamic acid (γ-PGA), with Pb2+ was studied using the polarographic method and circular dichroism measurement in soluble state. The number of available binding sites was determined based on the Chau's method and was found to be 0.04, 1.12, 3.56 and 4.51 mmol/(g dry weight of γ-PGA) at pH 3.4, 4.2, 5.0 and 6.2, respectively. Further, the number of binding sites was determined based on the Ruzic's method and was found to be 3.60 and 4.41 mmol/(g dry weight of γ-PGA) for pH 5.0 and 6.2, respectively. The constant (expressed as log K) values were 5.8 and 6.0 at pH 5.0 and 6.2. Compared to biopolymers secreted by other microorganisms, such as extracellular polymeric substances extraction from activated sludge, γ-PGA was a more efficient Pb2+ carrier from pH 5.0 to 6.2. The secondary structure of γ-PGA varied significantly when Pb2+ added. Ca2+ or Mg2+ replace a portion of the adsorbed Pb2+. However, the portion of Pb2+ involved in changing the γ-PGA conformation was not easily replaced by Ca2+ and Mg2+.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Coordination Complexes / chemistry*
Hydrogen-Ion Concentration
Ions / chemistry*
Lead / chemistry*
Models, Molecular
Molecular Conformation*
Polyglutamic Acid / analogs & derivatives*
Polyglutamic Acid / chemistry
Solubility
Spectrum Analysis

Substances

Coordination Complexes
Ions
poly(gamma-glutamic acid)
Polyglutamic Acid
Lead

Grants and funding

This work was funded by the National Natural Science Foundation of China (No. 21607031 to LLW, 51802046 to XLS) https://isisn.nsfc.gov.cn/egrantweb/, the Science Project of Guangdong Province, China (2018A030313656 to XLS) http://pro.gdstc.gov.cn/egrantweb/ and the Guangdong Province Science and Technology Innovation Strategy Special Fund (2018B020206001 to QS) http://pro.gdstc.gov.cn/egrantweb/. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.