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Biological homeostasis is a dynamic and elastic equilibrium of countless interlinked biochemical reactions. A key goal of life sciences is to understand these dynamics; bioengineers seek to reconfigure such networks. Both goals require the ability to monitor the concentration of individual intracellular metabolites with sufficient spatiotemporal resolution. To achieve this, a range of protein or protein/DNA signalling circuits with optical readouts have been constructed. Protein biosensors can provide quantitative information at subsecond temporal and suborganelle spatial resolution. However, their construction is fraught with difficulties related to integrating the affinity- and selectivity-endowing components with the signal reporters. We argue that development of efficient approaches for construction of chemically induced dimerisation systems and reporter domains with large dynamic ranges will solve these problems. Biosensors enable quantification of analytes of choice inside living cells. Protein biosensors can transform the way we monitor and engineer metabolism. The key challenges are to develop biosensors with large dynamic range and tuneable specificity. Ultimately, we seek to democratise this technology so that it is readily available to the scientific community. [ABSTRACT FROM AUTHOR]

Strigolactones (SLs) control plant development, enhance symbioses, and act as germination stimulants for some of the most destructive species of parasitic weeds, making SLs a potential tool to improve crop productivity and resilience. Field trials demonstrate the potential use of SLs as agrochemicals or genetic targets in breeding programs, with applications in improving drought tolerance, increasing yields, and controlling parasitic weeds. However, for effective translation of SLs into agriculture, understanding and exploiting SL diversity and the development of economically viable sources of SL analogs will be critical. Here we review how manipulation of SL signaling can be used when developing new tools and crop varieties to address some critical challenges, such as nutrient acquisition, resource allocation, stress tolerance, and plant–parasite interactions. Proof of principle for strigolactone (SL) application in agriculture has now been demonstrated at field-trial scale for parasitic weed control, increasing fruit yield, enhancing nutrient uptake, and improving yield under drought conditions. The agricultural potential of many emerging and established activities of SLs remains under-investigated. Specificity of activity in the landscape of many complex SL responses can be achieved through exploitation of differences in SL structures and receptor specificities. [ABSTRACT FROM AUTHOR]

Isoprenoids (terpenes/terpenoids) have many useful industrial applications, but are often not produced at industrially viable level in their natural sources. Synthetic biology approaches have been used extensively to reconstruct metabolic pathways in tractable microbial hosts such as yeast and re-engineer pathways and networks to increase yields. Here we review recent advances in this field, focusing on central carbon metabolism engineering to increase precursor supply, re-directing carbon flux for production of C10, C15, or C20 isoprenoids, and chemical decoration of high value diterpenoids (C20). We also overview other novel synthetic biology strategies that have potential utility in yeast isoprenoid pathway engineering. Finally, we address the question of what is required in the future to move the field forwards. [ABSTRACT FROM AUTHOR]

Isoprene and other plastidial isoprenoids are produced primarily from recently assimilated photosynthates via the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway. However, when environmental conditions limit photosynthesis, a fraction of carbon for MEP pathway can come from extrachloroplastic sources. The flow of extrachloroplastic carbon depends on the species and on leaf developmental and environmental conditions. The exchange of common phosphorylated intermediates between the MEP pathway and other metabolic pathways can occur via plastidic phosphate translocators. C 1 and C 2 carbon intermediates can contribute to chloroplastic metabolism, including photosynthesis and isoprenoid synthesis. Integration of these metabolic processes provide an example of metabolic flexibility, and results in the synthesis of primary metabolites for plant growth and secondary metabolites for plant defense, allowing effective use of environmental resources under multiple stresses. Highlights The high emission rates of isoprene under conditions of restricted photosynthesis can be associated with an increase in the availability of alternative carbon sources for the MEP pathway. The proposed shunt of carbon around the Calvin–Benson cycle involving glucose-6 phosphate could, at least partly, explain the incomplete 13C labeling of isoprene, which so far has been interpreted as uncoupling between isoprene and photosynthetic metabolism. The differences in the isoprene emission rate at different leaf developmental stages are related to overall changes in carbon partitioning between isoprenoid synthesis and primary metabolic pathways, and within the isoprenoid synthesis pathway, to dimethylallyl diphosphate (DMADP) by isoprene synthase and downstream prenyltransferase reactions. Limited availability of energetic cofactors and reducing equivalents can inhibit MEP pathway flux, resulting in an accumulation of MEP pathway intermediates and decreased carbon availability for isoprene production. [ABSTRACT FROM AUTHOR]

Abstract: Sucrose has economic and environmental advantages over glucose as a feedstock for bioprocesses. E. coli is widely used in industry, but the majority of current industrial E. coli strains cannot utilize sucrose. Previous attempts to transfer sucrose catabolic capabilities into non-sucrose-utilizing strains have met with limited success due to low growth rates on sucrose and phenotypic instability of the engineered strains. To address these problems, we developed a transferrable sucrose utilization cassette which confers efficient sucrose catabolism when integrated onto the E. coli chromosome. The cassette was based on the csc genes from E. coli W, a strain which grows very quickly on sucrose. Both plasmid-borne expression and chromosomal integration of a repressor-less sucrose utilizing cassette were investigated in E. coli strains K-12, B and C. In contrast to previous studies, strains harboring chromosomal cassettes could grow at the same rate as they do on glucose. Interestingly, we also discovered that spontaneous chromosomal integration of the csc genes was required to allow efficient growth from plasmid-transformed strains. The ability to engineer industrial strains for efficient sucrose utilization will allow substitution of sucrose for glucose in industrial fermentations. This will encourage the use of sucrose as a carbon source and assist in transition of our petrochemical-based economy to a bio-based economy. [Copyright &y& Elsevier]

Abstract: Sucrose has several advantages over glucose as a feedstock for bioprocesses, both environmentally and economically. However, most industrial Escherichia coli strains are unable to utilize sucrose. E. coli W can grow on sucrose but stops growing when sucrose concentrations become low. This is undesirable in fed-batch conditions where sugar levels are low between feeding pulses. Sucrose uptake rates were improved by removal of the cscR gene, which encodes a protein that represses expression of the sucrose utilization genes at low sucrose concentrations. Poly-3-hydroxybutyrate (PHB) was used as a model compound in order to assess the effect of improved sugar utilization on bio-production. In the cscR knockout strain, production from sucrose was improved by 50%; this strain also produced 30% more PHB than the wild-type using glucose. This result demonstrates the feasibility of utilizing sucrose as an industrial feedstock for E. coli-based bioprocesses in high cell density culture. [Copyright &y& Elsevier]