Inducible utilization pathways reflect widespread microbial strategies to uptake and consume sugars from the environment. Despite their broad importance and extensive characterization, little is known how these pathways naturally respond to their inducing sugar in individual cells. Here, we performed single-cell analyses to probe the behavior of representative pathways in the model bacterium Escherichia coli. We observed diverse single-cell behaviors, including uniform responses (D-lactose, D-galactose, N-acetylglucosamine, N-acetylneuraminic acid), “all-or-none” responses (D-xylose, L-rhamnose), and complex combinations thereof (L-arabinose, D-gluconate). Mathematical modeling and probing of genetically modified pathways revealed that the simple framework underlying these pathways—inducible transport and inducible catabolism—could give rise to most of these behaviors. Sugar catabolism was also an important feature, as disruption of catabolism eliminated tunable induction as well as enhanced memory of previous conditions. For instance, disruption of catabolism in pathways that respond to endogenously synthesized sugars led to full pathway induction even in the absence of exogenous sugar. Our findings demonstrate the remarkable flexibility of this simple biological framework, with direct implications for environmental adaptation and the engineering of synthetic utilization pathways as titratable expression systems and for metabolic engineering.

Only limited information is available regarding the manner in which cyclic carbonate and ester solvents coordinate Li + cations in electrolyte solutions for lithium batteries. One approach to gleaning significant insight into these interactions is to examine crystalline solvate structures. To this end, eight new solvate structures are reported with ethylene carbonate, γ-butyrolactone, and γ-valerolactone: (EC) 3 :LiClO 4 , (EC) 2 :LiClO 4 , (EC) 2 :LiBF 4 , (GBL) 4 :LiPF 6 , (GBL) 1 :LiClO 4 , (GVL) 1 :LiClO 4 , (GBL) 1 :LiBF 4 , and (GBL) 1 :LiCF 3 SO 3 . The crystal structure of (EC) 1 :LiCF 3 SO 3 is also re-reported for comparison. These structures enable the factors that govern the manner in which the ions are coordinated and the ion/solvent packingin the solid-stateto be scrutinized in detail.

Solvate crystal structures serve as useful models for the molecular-level interactions within the diverse solvates present in liquid electrolytes. Although acyclic carbonate solvents are widely used for Li-ion battery electrolytes, only three solvate crystal structures with lithium salts are known for these and related solvents. The present work, therefore, reports six lithium salt solvate structures with dimethyl and diethyl carbonate, (DMC)2:LiPF6, (DMC)1:LiCF3SO3, (DMC)1/4:LiBF4, (DEC)2:LiClO4, (DEC)1:LiClO4, and (DEC)1:LiCF3SO3 and four with the structurally related methyl and ethyl acetate, (MA)2:LiClO4, (MA)1:LiBF4, (EA)1:LiClO4, and (EA)1:LiBF4.

No abstract

Titratable systems are common tools in metabolic engineering to tune the levels of enzymes and cellular components as part of pathway optimization. For nonmodel microorganisms with limited genetic tools, inducible sugar utilization pathways offer built-in titratable systems. However, these pathways can exhibit undesirable single-cell behaviors that hamper the uniform and tunable control of gene expression. Here, we applied mathematical modeling and single-cell measurements of l-arabinose utilization in Escherichia coli to systematically explore how sugar utilization pathways can be altered to achieve desirable inducible properties. We found that different pathway alterations, such as the removal of catabolism, constitutive expression of high-affinity or low-affinity transporters, or further deletion of the other transporters, came with trade-offs specific to each alteration. For instance, sugar catabolism improved the uniformity and linearity of the response at the cost of requiring higher sugar concentrations to induce the pathway. Within these alterations, we also found that a uniform and linear response could be achieved with a single alteration: constitutively expressing the high-affinity transporter. Equivalent modifications to the d-xylose utilization pathway yielded similar responses, demonstrating the applicability of our observations. Overall, our findings indicate that there is no ideal set of typical alterations when co-opting natural utilization pathways for titratable control and suggest design rules for manipulating these pathways to advance basic genetic studies and the metabolic engineering of microorganisms for optimized chemical production.

No abstract

A Raman spectral evaluation of numerous crystalline solvates with lithium perchlorate (LiClO4) has been conducted over a wide temperature range. Two new solvate crystal structures(PMDETA)1:LiClO4 and (THF)1:LiClO4 with N,N,N′,N″,N″-pentamethyldiethylenetriamine and tetrahydrofuranhave been determined to aid in this study. With a help of density functional theory (DFT) and molecular dynamics (MD) simulations, the spectroscopic data have been correlated with varying modes of ClO4 –···Li+ cation coordination within the solvate structures to create a characterization tool to facilitate the Raman band assignments for the determination of ionic association interactions within solid and liquid electrolytes containing LiClO4. This study demonstrates that many of the spectroscopic evaluation conclusions reported in the scientific literature for LiClO4-based electrolytes are inaccurate.

An extensive correlation study has been conducted utilizing known LiCF3SO3 solvate crystal structures having specific modes of CF3SO3 –···Li+ ion coordination and the corresponding anion Raman vibrational band positions to delineate the assignments of specific vibrational bands to these ion coordination modes. To facilitate this study, three new crystalline solvate structures(12C4)2:LiCF3SO3, (BN)1:LiCF3SO3, and (MA)1:LiCF3SO3 with 12-crown-4 (12C4), butyronitrile (BN) and methyl acetate (MA)have been determined. The trifluoromethanesulfonate or “triflate” anion is an excellent probe for exploring electrolyte interactions since two separate Raman bands may be used for the evaluation and the anion exhibits a wide range of coordination modes in electrolytes with varying solvents.