Little is known about the cellular physiology of Escherichia coli at high cell densities (e.g., greater than 50 g [dry cell weight] per liter), particularly in relation to the cellular response to different growth conditions. E. coli W3100 cultures were grown under identical physical and nutritional conditions, by using a computercontrolled fermentation system which maintains the glucose concentration at 0.5 g/liter, to high cell densities at pH values of 6.0, 6.5, 7.0, and 7.5. The data suggest a relationship between the pH of the environment and the amount of acetate excreted by the organism during growth. At pH values of 6.0 and 6.5, the acetate reached a concentration of 6 g/liter, whereas at pH 7.5, the acetate reached a concentration of 12 g/liter. Furthermore, at pH values of 6.0 to 7.0, the E. coli culture undergoes a dramatic metabolic switch in which oxygen and glucose consumption and CO2 evolution all temporarily decrease by 50 to 80%, with a concomitant initiation of acetate utilization. After a 30-min pause in which approximately 50% of the available acetate is consumed, the culture recovers and resumes consuming glucose and oxygen and producing acetate and CO2 at preswitch levels. During the switch period, the specific activity of isocitrate lyase typically increases approximately fourfold.It is well known that during rapid aerobic growth, strains of Escherichia coli produce acetic acid as a by-product (7, 9-14, 17, 19), although the amount of acetate produced is strain dependent (17). Luli and Strohl (17) found that more than a threefold difference in acetate concentrations may occur between different strains grown in batch fermentations under identical conditions. The growth rate of the culture and the composition of the medium also influence the amount of acetate produced during growth. In chemostat experiments, acetate is not produced until the growth rate reaches a threshold value that is dependent upon the type of growth medium (21). E. coli cultures will produce acetate at a lower growth rate when grown in a nutrient-rich medium than in a defined medium (9, 21), and the specific acetate production rate also changes with the growth rate (9).Acetate is produced when the uptake of the primary carbon source is greater than its conversion to biomass and CO2 (10). The rate-limiting aspect of metabolism contributing to acetic acid formation by E. coli has been attributed to the electron transport system (7), the tricarboxylic acid cycle (10), or a combination of both (19). In a batch culture growing on glucose, approximately 15% of the carbon input is typically excreted as acetate (10).The presence of acetate in the growth medium can influence the physiology of the cell in many ways. Elevated acetate concentrations inhibit the growth rate of the culture, the effect of which may be more pronounced in complex medium than in defined medium (23). It has been postulated that the protonated form of acetate can cross the cytoplasmic membrane and reduce the proton motive force by decreasing ApH (7, 17), a...

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Purpose Coronavirus disease-2019 (COVID-19) is associated with a wide spectrum of clinical symptoms including acute respiratory failure. Biomarkers that can predict outcomes in patients with COVID-19 can assist with patient management. The aim of this study is to evaluate whether procalcitonin (PCT) can predict clinical outcome and bacterial superinfection in patients infected with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Methods Adult patients diagnosed with SARS-CoV-2 by nasopharyngeal PCR who were admitted to a tertiary care center in Boston, MA with SARS-CoV-2 infection between March 17 and April 30, 2020 with a baseline PCT value were studied. Patients who were presumed positive for SARS-CoV-2, who lacked PCT levels, or who had a positive urinalysis with negative cultures were excluded. Demographics, clinical and laboratory data were extracted from the electronic medical records. Results 324 patient charts were reviewed and grouped by clinical and microbiologic outcomes by day 28. Baseline PCT levels were significantly higher for patients who were treated for true bacteremia (p = 0.0005) and bacterial pneumonia (p = 0.00077) compared with the non-bacterial infection group. Baseline PCT positively correlated with the NIAID ordinal scale and survival over time. When compared to other inflammatory biomarkers, PCT showed superiority in predicting bacteremia. Conclusions Baseline PCT levels are associated with outcome and bacterial superinfection in patients hospitalized with SARS-CoV-2.

The development of dendritic arbors is critical in neuronal circuit formation, as dendrites are the primary sites of synaptic input. Morphologically specialized dendritic protrusions called spines represent the main postsynaptic compartment for excitatory neurotransmission. Recently, we demonstrated that chicken acidic leucine-rich epidermal growth factor (EGF) -like domain-containing brain protein/neuroglycan C (CALEB/NGC), a neural member of the EGF family, mediates dendritic tree and spine complexity but that the signaling pathways in the respective processes differ. For a more detailed characterization of these signal transduction pathways, we performed a yeast two-hybrid screen to identify proteins that interact with CALEB/NGC. Our results show that B56beta, a regulatory subunit of protein phosphatase 2A, interacts with CALEB/NGC and inhibits CALEB/NGC-mediated dendritic branching but not spine formation. Binding of B56beta to CALEB/NGC was confirmed by several biochemical and immunocytochemical assays. Using affinity chromatography and mass spectrometry, we demonstrate that the whole protein phosphatase 2A trimer, including structural and catalytic subunits, binds to CALEB/NGC via B56beta. We show that CALEB/NGC induces the phosphorylation of Akt in dendrites. Previously described to interfere with Akt signaling, B56beta inhibits Akt phosphorylation and Akt-dependent dendritic branching but not Akt-independent spine formation induced by CALEB/NGC. Our results contribute to a better understanding of signaling specificity leading to neuronal process differentiation in sequential developmental events.