Biology subjects

Erb, T.

Publications and source records attributed to Erb, T..

3 recordsLinked to original sources

bioRxiv2023

Design, construction and optimization of formaldehyde growth biosensors with broad application in Biotechnology

Formaldehyde is a key metabolite in natural and synthetic one-carbon metabolism as well as an important environmental toxin with high toxicity at low concentrations. To engineer efficient formaldehyde producing enzymes and to detect formaldehyde in industrial or environmental samples, it is important to establish highly sensitive, easy to use and affordable formaldehyde detection methods. Here, we transformed the workhorse bacterium Escherichia coli into biosensors that can detect a broad range of formaldehyde concentrations. Based on natural and promiscuous formaldehyde assimilation enzymes, we designed and engineered three different E. coli strains that depend on formaldehyde assimilation for cellular growth. After in depth characterization of these biosensors, we show that the formaldehyde sensitivity can be improved through adaptive laboratory evolution or modification of metabolic branch points. The metabolic engineering strategy presented in this work allowed the creation of E. coli biosensors that can detect formaldehyde in a concentration range from [~]30 M to [~]13 mM. Using the most sensitive strain, we benchmarked the in vivo activities of different, widely used NAD-dependent methanol dehydrogenases, the rate-limiting enzyme in synthetic methylotrophy. We also show that the strains can grow upon external addition of formaldehyde indicating their potential use for applications beyond enzyme engineering. The formaldehyde biosensors developed in this study are fully genomic and can be used as plug and play devices for screening large enzyme libraries. Thus, they have the potential to greatly advance enzyme engineering and might even be used for environmental monitoring or analysis of industrial probes. Highlights- Conversion of E. coli into three different formaldehyde growth biosensors - Biosensors are fully genomic and grow robustly when formaldehyde is present - Biosensors can detect formaldehyde concentrations ranging from [~]30 M to [~]13 mM - Benchmarking of biotechnological relevant methanol dehydrogenases reveals potential of biosensors for enzyme engineering - Biosensors grow upon direct addition of formaldehyde indicating potential use in environmental or industrial settings

bioengineering↗

bioRxiv2022

On the flexibility of the cellular amination network in E. coli

Ammonium (NH4+) is essential to generate the nitrogenous building blocks of life. It gets assimilated via the canonical biosynthetic routes to glutamate and is further distributed throughout metabolism via a network of transaminases. To study the flexibility of this network, we constructed an Escherichia coli glutamate auxotrophic strain. This strain allowed us to systematically study which amino acids serve as amine source and found that several amino acids complement the auxotrophy, either by producing glutamate via transamination reactions or by their conversion to glutamate. In this network, we identified aspartate transaminase AspC as a major connector between many amino acids and glutamate. Additionally, we extended the transaminase network by the amino acids {beta}-alanine, alanine, glycine and serine as new amine sources and identified D-amino acid dehydrogenase (DadA) as an intracellular amino acid sink removing substrates from transaminase reactions. Finally, ammonium assimilation routes producing aspartate or leucine were introduced. Our study reveals the high flexibility of the cellular amination network, both in terms of transaminase promiscuity and adaptability to new connections and ammonium entry points.

systems biology↗

bioRxiv2019

Sulfur-oxidizing symbionts without canonical genes for autotrophic CO2 fixation

Since the discovery of symbioses between sulfur-oxidizing (thiotrophic) bacteria and invertebrates at hydrothermal vents over 40 years ago, it has been assumed that autotrophic fixation of CO2 by the symbionts drives these nutritional associations. In this study, we investigated Candidatus Kentron, the clade of symbionts hosted by Kentrophoros, a diverse genus of ciliates which are found in marine coastal sediments around the world. Despite being the main food source for their hosts, Kentron lack the key canonical genes for any of the known pathways for autotrophic fixation, and have a carbon stable isotope fingerprint unlike other thiotrophic symbionts from similar habitats. Our genomic and transcriptomic analyses instead found metabolic features consistent with growth on organic carbon, especially organic and amino acids, for which they have abundant uptake transporters. All known thiotrophic symbionts have converged on using reduced sulfur to generate energy lithotrophically, but they are diverse in their carbon sources. Some clades are obligate autotrophs, while many are mixotrophs that can supplement autotrophic carbon fixation with heterotrophic capabilities similar to those in Kentron. We have shown that Kentron are the only thiotrophic symbionts that appear to be entirely heterotrophic, unlike all other thiotrophic symbionts studied to date, which possess either the Calvin-Benson-Bassham or reverse tricarboxylic acid cycles for autotrophy. Significance StatementMany animals and protists depend on symbiotic sulfur-oxidizing bacteria as their main food source. These bacteria use energy from oxidizing inorganic sulfur compounds to make biomass autotrophically from CO2, serving as primary producers for their hosts. Here we describe apparently non-autotrophic sulfur symbionts called Kentron, associated with marine ciliates. They lack genes for known autotrophic pathways, and have a carbon stable isotope fingerprint heavier than other symbionts from similar habitats. Instead they have the potential to oxidize sulfur to fuel the uptake of organic compounds for heterotrophic growth, a metabolic mode called chemolithoheterotrophy that is not found in other symbioses. Although several symbionts have heterotrophic features to supplement primary production, in Kentron they appear to supplant it entirely.

microbiology↗