Biology subjects

Nikel, P. I.

Publications and source records attributed to Nikel, P. I..

3 recordsLinked to original sources

bioRxiv2018

Biotransformation of 2,4-dinitrotoluene in a phototrophic co-culture of engineered Synechococcus elongatus and Pseudomonas putida

In contrast to the current paradigm of using microbial monocultures in most biotechnological applications, increasing efforts are being directed towards engineering mixed-species consortia to perform functions that are difficult to program into individual strains. Additionally, the division of labor between specialist species found in natural consortia can lead to increased catalytic efficiency and stability relative to a monoculture or a community composed of generalists. In this work, we have designed a synthetic co-culture for phototrophic degradation of xenobiotics, composed of a cyanobacterium, (Synechococcus elongatus PCC 7942) and a heterotrophic bacterium (Pseudomonas putida EM173). Cyanobacteria fix CO2 through photosynthetic metabolism and secrete sufficient carbohydrates to support the growth and active metabolism of P. putida, which has been engineered to consume sucrose as the only carbon source and to degrade the environmental pollutant 2,4-dinitrotoluene (2,4-DNT). The synthetic consortium is able to degrade 2,4-DNT with only light and CO2 as inputs for the system, and it was stable over time through repeated backdilutions. Furthermore, cycling this consortium through low nitrogen medium promoted the accumulation of polyhydroxyalkanoate (PHA)-an added-value biopolymer-in P. putida, thus highlighting the versatility of this production platform. Altogether, the synthetic consortium allows for simultaneous bioproduction of PHA and remediation of the industrial pollutant 2,4-DNT, using light and CO2 as inputs.\n\nImportanceIn this study, we have created an artificial consortium composed of two bacterial species that enables the degradation of the industrially-produced environmental pollutant 2,4-DNT while simultaneously producing PHA bioplastic. In these co-cultures, the photosynthetic cyanobacteria fuel an engineered P. putida strain programmed both to use sucrose as a carbon source and to perform the biotransformation of 2,4-DNT. The division of labor in this synthetic co-culture is reminiscent of that commonly observed in microbial communities and represents a proof-of-principle example of how artificial consortia can be employed for bioremediation purposes. Furthermore, this co-culture system enabled the utilization of freshwater sources that could not be utilized in classical agriculture settings, reducing the potential competition of this alternative method of bioproduction with current agricultural practices, as well as remediation of contaminated water streams.

synthetic biology↗

bioRxiv2018

Complete decoupling of bacterial growth from biopolymer production through proteolytic control of enzyme levels

Most current methods for controlling the rate of formation of a key protein or enzyme in cell factories rely on the manipulation of target genes within the pathway. In this article, we present a novel synthetic system for post-translational regulation of protein levels, FENIX, which provides both independent control of the steady-state protein level and inducible accumulation of targeted proteins. The device is based on the constitutive, proteasome-dependent degradation of the target polypeptide by tagging with a short synthetic, hybrid NIa/SsrA amino acid sequence in the C-terminal domain. The protein degradation process can be reversed by activating the system via addition of an orthogonal inducer (e.g. 3-methylbenzoate) to the culture medium. The system was benchmarked in Escherichia coli by tagging two fluorescent proteins (GFP and mCherry) and further exploited for engineering poly(3-hydroxybutyrate) (PHB) accumulation completely uncoupled from bacterial growth. By tagging PhaA (3-ketoacyl-CoA thiolase, first step of the route), a dynamic metabolic switch at the acetyl-coenzyme A node was established in such a way that this metabolic precursor could be effectively directed into PHB formation upon activation of the system. The engineered E. coli strain reached a very high specific rate of PHB accumulation with a polymer content of ca. 72% (w/w) in glucose cultures set in the growth-decoupled mode. Thus, FENIX enables dynamic control of metabolic fluxes in bacterial cell factories by establishing post-translational synthetic switches in the pathway of interest.\n\n\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=109 SRC=\"FIGDIR/small/389809_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (34K):\norg.highwire.dtl.DTLVardef@1d9ec08org.highwire.dtl.DTLVardef@1722feorg.highwire.dtl.DTLVardef@fa77b2org.highwire.dtl.DTLVardef@1c8624a_HPS_FORMAT_FIGEXP M_FIG GRAPHICAL ABSTRACT C_FIG

synthetic biology↗

bioRxiv2018

The metabolic redox regime of Pseudomonas putida tunes its evolvability towards novel xenobiotic substrates

During evolution of biodegradation pathways for xenobiotic compounds, the transition towards novel substrates of Rieske non-heme iron oxygenases borne by environmental bacteria is frequently associated with faulty reactions. Such reactions release reactive oxygen species (ROS), endowed with high mutagenic potential. The present work studies how the operation of a given metabolic network by a bacterial host may either foster or curtail the still-evolving biochemical pathway for catabolism of 2,4-dinitrotoluene (2,4-DNT). To this end, the genetically tractable strain Pseudomonas putida EM173 was chromosomally implanted with a Tn7 construct carrying the whole genetic complement (recruited from the environmental isolate Burkholderia sp. R34) necessary for complete biodegradation of 2,4-DNT. By using reporter technology and direct measurements of ROS formation, we observed that the engineered P. putida strain experienced oxidative stress when catabolizing the nitroaromatic substrate. However, ROS was neither translated into significant activation of the SOS response to DNA damage nor resulted in a mutagenic regime (unlike Burkholderia sp. R34, the original host of the pathway). To inspect whether the tolerance of P. putida to oxidative insults could be traced to its characteristic reductive redox regime, we artificially lowered the pool of NAD(P)H by conditional expression of a water forming, NADH-specific oxidase. Under the resulting low-NAD(P)H status, 2,4-DNT triggered a conspicuous mutagenic and genomic diversification scenario. These results indicate that the background biochemical network of environmental bacteria ultimately determines the evolvability of metabolic pathways. Moreover, the data explains the efficacy of some bacteria such as Pseudomonads to host and evolve new catabolic routes.\n\nIMPORTANCESome environmental bacteria evolve new capacities for aerobic biodegradation of chemical pollutants by adapting pre-existing redox reactions to recently faced compounds. The process typically starts by co-option of enzymes of an available route to act on the chemical structure of the substrates-to-be. The critical bottleneck is generally the first biochemical step and most of the selective pressure operates on reshaping the initial reaction. In Rieske non-heme iron oxygenases, the interim uncoupling of the novel substrate to the old enzymes results in production of highly mutagenic ROS. In this work, we demonstrate that the background metabolic regime of the bacterium that hosts an evolving catabolic pathway (e.g. biodegradation of the xenobiotic 2,4-DNT) determines whether the cells would either adopt a genetic diversification regime or a robust ROS-tolerant state. These results expose new perspectives to contemporary attempts for rational assembly of whole-cell biocatalysts, as pursued by present-day metabolic engineering.

microbiology↗