Construction of a self-luminescent cyanobacterial bioreporter that detects a broad range of bioavailable heavy metals in aquatic environments

Abstract

A self-luminescent bioreporter strain of the unicellular cyanobacterium Synechococcus sp. PCC 7942 was constructed by fusing the promoter region of the smt locus (encoding the transcriptional repressor SmtB and the metallothionein SmtA) to luxCDABE from Photorhabdus luminescens; the sensor smtB gene controlling the expression of smtA was cloned in the same vector. The bioreporter performance was tested with a range of heavy metals and was shown to respond linearly to divalent Zn, Cd, Cu, Co, Hg, and monovalent Ag. Chemical modeling was used to link bioreporter response with metal speciation and bioavailability. Limits of Detection (LODs), Maximum Permissive Concentrations (MPCs) and dynamic ranges for each metal were calculated in terms of free ion concentrations. The ranges of detection varied from 11 to 72 pM for Hg2+ (the ion to which the bioreporter was most sensitive) to 1.54–5.35 μM for Cd2+ with an order of decreasing sensitivity as follows: Hg2+ >> Cu2+ >> Ag+ > Co2+ ≥ Zn2+ > Cd2+. However, the maximum induction factor reached 75-fold in the case of Zn2+ and 56-fold in the case of Cd2+, implying that Zn2+ is the preferred metal in vivo for the SmtB sensor, followed by Cd2+, Ag+ and Cu2+ (around 45–50-fold induction), Hg2+ (30-fold) and finally Co2+ (20-fold). The bioreporter performance was tested in real environmental samples with different water matrix complexity artificially contaminated with increasing concentrations of Zn, Cd, Ag, and Cu, confirming its validity as a sensor of free heavy metal cations bioavailability in aquatic environments.

Development of a Sensitive Escherichia coli Bioreporter Without Antibiotic Markers for Detecting Bioavailable Copper in Water Environments

“…Hence, it is difficult to apply at the grassroots level or in the field. Besides, quantification by these methods reflects the total copper content, including both bioavailable and non-bioavailable fractions (Martin-Betancor et al, 2015), making it difficult to objectively assess the toxicity of heavy metals. Therefore, developing an inexpensive, sensitive, selective, and portable method to determine the bioavailability of copper is necessary.…”

Construction of a sensitive and specific lead biosensor using a genetically engineered bacterial system with a luciferase gene reporter

“…Biosensors are used in various designs with different reporters and promoters. At low concentration of heavy bioavailable metals, bioluminescence signals are likely to be suitable [19,20]. They can also be applied to monitoring bioavailable concentrations of heavy metal [21][22][23][24][25][26][27] and piezoelectric biosensors [28][29][30] as enzymebased electrochemical biosensors.…”

Cry Protein Crystal-Immobilized Metallothioneins for Bioremediation of Heavy Metals from Water

“…Like other metallothioneins, this use of cysteines to ligate the metal ions provides SmtA with selectivity towards soft metals such as Hg 2+ , Cd 2+ , Zn 2+ , Cu 2+ , and Co 2+ , allowing it to be used as a metal chelator of toxic heavy metals such as Cd 2+ -even in the presence of high concentrations of sodium, calcium, and magnesium [27,28]. This property makes them potentially useful for multiple purposes [15,[29][30][31][32][33], including as binding agents for the selective removal of heavy atoms from contaminated water [27]. Here we describe the in vivo production and physical characterization of three different Cry3Aa-SmtA fusion crystals, and the evaluation of their ability to remove Cd 2+ and Cr 3+ ions from heavy metal-containing solutions.…”