Oleate metabolism using kinetic 13C dilution strategy deciphered the potential role of global transcription regulator arcA in Escherichia coli

Microbial metabolism of long-chain fatty acids (LCFA; > C12) is of relevance owing to their presence in various nutrient niches. Microbes have evolved to metabolize LCFA by expressing relevant genes coordinated by various transcriptional regulators. Among the global transcriptional regulators, the metabolic control conferred by arcA (aerobic respiration control) under a LCFA medium is lacking. This work is targeted to unravel the metabolic features of E.coli MG1655 and its knockout strain ΔarcA under oleate (C18:1) as a sole carbon source, providing novel insights into the flexibility of the global regulators in maintaining the cellular physiology. Owing to the availability and cost of stable isotope LCFA tracers, we adopted a novel kinetic 13C dilution strategy. This allowed us to quantify the 13C dilution rates in the amino acids that retro-biosynthetically shed light on the central metabolic pathways in actively growing cells. Our data comprehensively mapped oleate oxidization in E.coli via the pathways of β-oxidation, TCA cycle, anaplerotic and gluconeogenesis. Interestingly, arcA knockout showed expeditious growth (~60%) along with an increased oleate utilization rate (~55%) relative to the wild-type. ΔarcA also exhibited higher 13C dilution rates (> 20%) in proteinogenic amino acids than the wild-type. Overall, the study established the de-repression effect conferred by ΔarcA in E.coli, which resulted in a phenotype with reprogrammed metabolism favouring higher oleate assimilation. The outcomes suggest rational metabolic engineering of regulators as a strategy to develop smart cells for enhanced biotransformation of LCFA. This study also opens an avenue for adopting a kinetic 13C dilution strategy to decipher the cellular metabolism of a plethora of substrates, including other LCFA in microbes.

Piggybacking on niche-adaptation reduces the cost of multidrug resistance plasmids

The persistence of plasmids in bacterial populations represents a puzzling evolutionary problem with serious clinical implications due to their role in the ongoing antibiotic resistance crisis. Recently, major advancements have been made towards resolving this “plasmid paradox” but mainly in a non-clinical context. Here we propose an additional explanation for the maintenance of multidrug resistance (MDR) plasmids in clinical Escherichia coli strains. After co-evolving two MDR plasmids encoding last resort carbapenem resistance with an extraintestinal pathogenic E. coli strain, we observed that chromosomal media adaptive mutations in the global regulatory systems CCR (Carbon Catabolite Repression) and ArcAB (Aerobic Respiration Control) pleiotropically mitigated the costs of both plasmids. Mechanistically, cost reductions were due to a net downregulation of plasmid gene expression. Our results suggest that global chromosomal transcriptional re-wiring during bacterial niche-adaptation may facilitate plasmid maintenance.

Sniff-invariant intensity perception using olfactory bulb coding of inhalation dynamics

SummaryFor stable perception of odor intensity, there must exist a neural correlate that is invariant across other parameters, such as the highly variable sniff cycle. Previous hypotheses suggest that variance in inhalation dynamics alters odor concentration profiles in the naris despite a constant environmental concentration. Using whole cell recordings in the olfactory bulb of awake mice, we directly demonstrate that rapid sniffing mimics the effect of odor concentration increase at the level of both mitral and tufted cell (MTC) firing rate responses and temporal responses. In contrast, we find that mice are capable of discriminating concentrations within short timescales despite highly variable sniffing behavior. We reason that the only way the olfactory system can differentiate between a change in sniffing and a change in concentration is to receive information about the inhalation parameters in parallel with information about the odor. While conceivably this could be achieved via corollary discharge from respiration control centres, we find that the sniff-driven activity of MTCs without odor input is informative of the kind of inhalation that just occurred, allowing rapid detection of a change in inhalation. Thus, a possible reason for sniff modulation of the early olfactory system may be to inform downstream centres of nasal flow dynamics, so that an inference can be made about environmental concentration independent of sniff variance.

A ROLE OF STRUCTURAL-FUNCTIONAL PARTICULARITIES OF RETICULAR GIGANTOCELLULAR NUCLEUS DIFFERENT POINTS IN CENTRAL RESPIRATION CONTROL MECHANISMS

New data concerning role of reticular gigantocellular nucleus respiratory areasin respiratory pattern forming is discussed. Based on electrical stimulation ofnucleus inspiratory and expiratory points results, authors suggest that reticulargigantocellular nucleus plays a considerable role in central respiration controlmechanisms.