Biocatalysis on the surface of Escherichia coli: melanin pigmentation of the cell exterior

Abstract

Today, it is considered state-of-the-art to engineer living organisms for various biotechnology applications. Even though this has led to numerous scientific breakthroughs, the enclosed interior of bacterial cells still restricts interactions with enzymes, pathways and products due to the mass-transfer barrier formed by the cell envelope. To promote accessibility, we propose engineering of biocatalytic reactions and subsequent product deposition directly on the bacterial surface. As a proof-of-concept, we used the AIDA autotransporter vehicle for Escherichia coli surface expression of tyrosinase and fully oxidized externally added tyrosine to the biopolymer melanin. This resulted in a color change and creation of a black cell exterior. The capture of ninety percent of a pharmaceutical wastewater pollutant followed by regeneration of the cell bound melanin matrix through a simple pH change, shows the superior function and facilitated processing provided by the surface methodology. The broad adsorption spectrum of melanin could also allow removal of other micropollutants.

Enzymatic Bioremediation of Organophosphate Compounds—Progress and Remaining Challenges

“…The adaptability and versatility of plants and microbes has enabled bioremediation as a “biologically-friendly” strategy to eliminate many of the harmful contaminants released by the everyday machinations of human society, see schematic overview in Figure 1. At present, bioremediation of environmental reservoirs is accomplished using primarily natural, non-engineered bacteria that have been isolated from contaminated sources and exhibit an ability to consume or convert the target contaminant as highlighted in several examples (Cologgi et al, 2011; Silar et al, 2011; Dubinsky et al, 2013; Prakash et al, 2013; Gustavsson et al, 2016). With the rise of synthetic biology and microbial engineering, future strategies may likely include engineered microbes containing novel metabolic pathways or tailored for enhanced fitness in austere environments.…”

Melanin Produced by the Fast-Growing Marine Bacterium Vibrio natriegens through Heterologous Biosynthesis: Characterization and Application

“…S1 in the supplemental material) (12). With recombinant DNA technology, the tyrosinase gene has previously been cloned and heterologously expressed in Escherichia coli, and the resulting melanin was tested in a variety of applications (13,14).…”

Microbial melanins for radioprotection and bioremediation

“…Apart from limiting the use of non-pathogenic species, possible mechanisms to overcome this limitation include the attenuation of virulence by genetic or chemical manipulations or the transformation of nonpathogenic species with melanin production capacity. For example, Escherichia coli can be genetically engineered to melanize its surface and later remove pharmaceutical pollutants from wastewater with high efficiency (Gustavsson et al, 2016).…”

“…(Cordero and Casadevall, 2017). Melanin's broad absorption of electromagnetic energy combined with adsorption of radiation energy and chemicals respectively, make melanin-producing microorganisms particularly useful for radioprotection and bioremediation processes (Revskaya et al, 2012;Gustavsson et al, 2016). Melanin biosynthesis in fungi has also been related to the assimilatory metabolism of priority pollutants (Prenafeta-Bold u et al, 2006).…”