Enhancing Escherichia coli abiotic stress resistance through ornithine lipid formation

Escherichia coli is a common host for biotechnology and synthetic biology applications. During growth and fermentation, the microbes are often exposed to stress conditions, such as variations in pH or solvent concentrations. Bacterial membranes play a key role in response to abiotic stresses. Ornithine lipids (OLs) are a group of membrane lipids whose presence and synthesis have been related to stress resistance in bacteria. We wondered if this stress resistance could be transferred to bacteria not encoding the capacity to form OLs in their genome, such as E. coli. In this study, we engineered different E. coli strains to produce unmodified OLs and hydroxylated OLs by expressing the synthetic operon olsFC. Our results showed that OL formation improved pH resistance and increased biomass under phosphate limitation. Transcriptome analysis revealed that OL-forming strains differentially expressed stress- and membrane-related genes. OL-producing strains also showed better growth in the presence of the ionophore carbonyl cyanide 3-chlorophenylhydrazone (CCCP), suggesting reduced proton leakiness in OL-producing strains. Furthermore, our engineered strains showed improved heterologous violacein production at phosphate limitation and also at low pH. Overall, this study demonstrates the potential of engineering the E. coli membrane composition for constructing robust hosts with an increased abiotic stress resistance for biotechnology and synthetic biology applications. KEY POINTS: • Ornithine lipid production in E. coli increases biomass yield under phosphate limitation. • Engineered strains show an enhanced production phenotype under low pH stress. • Transcriptome analysis and CCCP experiments revealed reduced proton leakage.

Electrostatic Fermentation: Molecular Response Insights for Tailored Beer Production

Electrostatic fermentation avoids the cellular redox imbalance of traditional fermentation, but knowledge gaps exist. This study explores the impact of electrostatic fermentation on the growth, volatile profile, and genetic response of Saccharomyces pastorianus Saflager S-23. The applied voltage (15 and 30 V) in the electrostatic fermentation system increased the growth and substrate utilization of S. pastorianus while decreasing ethanol production. The aromas typically associated with traditional fermentation, such as alcoholic, grape, apple, and sweet notes, were diminished, while aromas like roses, fruits, flowers, and bananas were augmented in electrostatic fermentation. RNA-seq analysis revealed upregulation of genes involved in cell wall structure, oxidoreductase activity, and iron ion binding, while genes associated with protein synthesis, growth control, homeostasis, and membrane function were downregulated under the influence of applied voltage. The electrostatic fermentation system modulates genetic responses and metabolic pathways in yeast, rendering it a promising method for tailored beer production. Demonstrating feasibility under industrial-scale and realistic conditions is crucial for advancing towards commercialization.

Dynamic proteome allocation regulates the profile of interaction of auxotrophic bacterial consortia

Microbial ecosystems are composed of multiple species in constant metabolic exchange. A pervasive interaction in microbial communities is metabolic cross-feeding and occurs when the metabolic burden of producing costly metabolites is distributed between community members, in some cases for the benefit of all interacting partners. In particular, amino acid auxotrophies generate obligate metabolic inter-dependencies in mixed populations and have been shown to produce a dynamic profile of interaction that depends upon nutrient availability. However, identifying the key components that determine the pair-wise interaction profile remains a challenging problem, partly because metabolic exchange has consequences on multiple levels, from allocating proteomic resources at a cellular level to modulating the structure, function and stability of microbial communities. To evaluate how ppGpp-mediated resource allocation drives the population-level profile of interaction, here we postulate a multi-scale mathematical model that incorporates dynamics of proteome partition into a population dynamics model. We compare our computational results with experimental data obtained from co-cultures of auxotrophic Escherichia coli K12 strains under a range of amino acid concentrations and population structures. We conclude by arguing that the stringent response promotes cooperation by inhibiting the growth of fast-growing strains and promoting the synthesis of metabolites essential for other community members.

Plasmid DNA Production in Proteome-Reduced Escherichia coli

The design of optimal cell factories requires engineering resource allocation for maximizing product synthesis. A recently developed method to maximize the saving in cell resources released 0.5% of the proteome of Escherichia coli by deleting only three transcription factors. We assessed the capacity for plasmid DNA (pDNA) production in the proteome-reduced strain in a mineral medium, lysogeny, and terrific broths. In all three cases, the pDNA yield from biomass was between 33 and 53% higher in the proteome-reduced than in its wild type strain. When cultured in fed-batch mode in shake-flask, the proteome-reduced strain produced 74.8 mg L^-1 pDNA, which was four times greater than its wild-type strain. Nevertheless, the pDNA supercoiled fraction was less than 60% in all cases. Deletion of recA increased the pDNA yields in the wild type, but not in the proteome-reduced strain. Furthermore, recA mutants produced a higher fraction of supercoiled pDNA, compared to their parents. These results show that the novel proteome reduction approach is a promising starting point for the design of improved pDNA production hosts.

Trade-offs between gene expression, growth and phenotypic diversity in microbial populations

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Limitations in molecular resources for gene expression influence bacterial physiology.

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Bacteria optimise trade-offs between resource allocation and growth.

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Resource allocation plays a role in the emergence of phenotypic heterogeneity.

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Trade-offs between bet-hedging and growth can be harnessed in biotechnology.

Bacterial cells have a limited number of resources that can be allocated for gene expression. The intracellular competition for these resources has an impact on the cell physiology. Bacteria have evolved mechanisms to optimize resource allocation in a variety of scenarios, showing a trade-off between the resources used to maximise growth (e.g. ribosome synthesis) and the rest of cellular functions. Limitations in gene expression also play a role in generating phenotypic diversity, which is advantageous in fluctuating environments, at the expenses of decreasing growth rates. Our current understanding of these trade-offs can be exploited for biotechnological applications benefiting from the selective manipulation of the allocation of resources.

Bacterial Diversity and Population Dynamics During the Fermentation of Palm Wine From Guerrero Mexico

Palm wine is obtained by fermentation of palm tree sap. In the Pacific coast of Mexico, palm wine is called Tuba and it is consumed as a traditional fermented beverage. Tuba has empirical applications such as an auxiliary in gastrointestinal diseases and a good source of nutrients. In the present study, a next-generation sequencing of the V3-V4 regions of the 16S rRNA gene was employed to analyze bacterial diversity and population dynamics during the fermentation process of Tuba, both in laboratory controlled conditions and in commercial samples from local vendors. Taxonomic identification showed that Fructobacillus was the main genus in all the samples, following by Leuconostoc, Gluconacetobacter, Sphingomonas, and Vibrio. Alpha diversity analysis demonstrated variability between all the samples. Beta diversity clustered the bacterial population according to the collection origin of the sample. Metabolic functional profile inference showed that the members of the bacterial communities may present the vitamin, antibiotic and antioxidant biosynthesis genes. Additionally, we further investigated the correlation between the predominant genera and some composition parameters of this beverage. This study provides the basis of the bacterial community composition and functionality of the fermented beverage.

Production of d-lactate from sugarcane bagasse and corn stover hydrolysates using metabolic engineered Escherichia coli strains

In this study, the lactogenic Escherichia coli strain JU15 was used and modified to produce d-lactate (d-LA) from plant hydrolysates with a minimal nutrient addition in pH controlled fermenters. Results showed that strain JU15 produces d-LA with high yield and productivity in laboratory simulated hydrolysate media and actual sugar cane bagasse hemicellulosic hydrolysate. Strain JU15 showed sequential carbon source utilization and acetic acid production. The l-lactic and acetic acid production pathways were deleted in JU15, resulting strain AV03 (JU15 ΔpoxB, ΔackA-pta, ΔmgsA), which showed simultaneous consumption of glucose and xylose and no acetic acid production in the simulated hydrolysate. The d-LA yield from hydrolysate sugars was close to 0.95gD-LA/gsugars in all cases. Our results show that d-LA can be produced from plant hydrolysates in simple batch fermentation processes with a high productivity using engineered E. coli strains at fermenter scales from 0.2 up to 10L.

Sclerosis in bisphosphonate-related osteonecrosis of the jaws and its correlation with the clinical stages: study of 43 cases

We analysed the degree of sclerosis in the different stages of bisphosphonate-related osteonecrosis of the jaws (BRONJ) and studied the relation between the grade of sclerosis, the clinical symptoms, and the depth of lucency. We compared 43 patients with mandibular BRONJ with a control group of 40 cases with no bony lesions. The presence of sclerotic bone, cortical irregularities, radiolucency, fragmentation or sequestration, periostitis, and narrowing of the mandibular canal were studied from computed tomographic (CT) scans using the program ImageJ 1.47v (National Institute of Health, Bethesda, USA) to measure the radiolucency, width of the cortices, and degree of sclerosis. Patients with BRONJ had more severe sclerosis than controls (p<0.01). There was also a significant difference among the different stages of BRONJ, with the highest values found in stage III (p=0.02). The degree of sclerosis differed according to sex, type of bisphosphonate, and the clinical characteristics such as pain, or suppuration, but not significantly so (p>0.05). We conclude that the degree of sclerosis increases with the clinical stage of BRONJ, and is correlated with the depth of lucency.

Metabolic and transcriptional response of Escherichia coli with a NADP(+)-dependent glyceraldehyde 3-phosphate dehydrogenase from Streptococcus mutans

The NAD(+)-dependent glyceraldehyde-3-phosphate-dehydrogenase (NAD(+)-GAPDH) is a key enzyme to sustain the glycolytic function in Escherichia coli and to generate NADH. In the absence of NAD(+)-GAPDH activity, the glycolytic function can be restored through NADP(+)-dependent GAPDH heterologous expression. Here, some metabolic and transcriptional effects are described when the NAD(+)-GAPDH gene from E. coli (gapA) is replaced with the NADP(+)-GAPDH gene from Streptococcus mutans (gapN). Expression of gapN was controlled by the native gapA promoter (E. coliΔgapA::gapN) or by the constitutive trc promoter in a multicopy plasmid (E. coliΔgapA::gapN/pTrcgapN). The specific NADP(+)-GAPDH activity was 4.7 times higher in E. coliΔgapA::gapN/pTrcgapN than E. coliΔgapA::gapN. Growth, glucose consumption and acetic acid production rates increased in agreement with the NADP(+)-GAPDH activity level. Analysis of E. coliΔgapA::gapN/pTrcgapN showed that although gapN expression complemented NAD(+)-GAPDH activity, the resulting low NADH levels decreased the expression of the respiratory chain and oxidative phosphorylation genes (ndh, cydA, cyoB and atpA). In comparison with the wild type strain, E. coliΔgapA::gapN/pTrcgapN decreased the percentage of mole of oxygen consumed per mole of glucose metabolized by 40 % with a concomitant reduction of 54 % in the ATP/ADP ratio. The cellular response to avoid NADPH excess led to the overexpression of the transhydrogenase coded by udhA and the down-regulation of the pentose-phosphate and Krebs cycle genes, which reduced the CO2 production and increased the acetic acid synthesis. The E. coli strains obtained in this work can be useful for future metabolic engineering efforts aiming for the production of metabolites which biosynthesis depends on NADPH.

Engineering the Escherichia coli fermentative metabolism

Fermentative metabolism constitutes a fundamental cellular capacity for industrial biocatalysis. Escherichia coli is an important microorganism in the field of metabolic engineering for its well-known molecular characteristics and its rapid growth. It can adapt to different growth conditions and is able to grow in the presence or absence of oxygen. Through the use of metabolic pathway engineering and bioprocessing techniques, it is possible to explore the fundamental cellular properties and to exploit its capacity to be applied as industrial biocatalysts to produce a wide array of chemicals. The objective of this chapter is to review the metabolic engineering efforts carried out with E. coli by manipulating the central carbon metabolism and fermentative pathways to obtain strains that produce metabolites with high titers, such as ethanol, alanine, lactate and succinate.

ATP limitation in a pyruvate formate lyase mutant of Escherichia coli MG1655 increases glycolytic flux to D-lactate

A derivative strain of Escherichia coli MG1655 for D-lactate production was constructed by deleting the pflB, adhE and frdA genes; this strain was designated "CL3." Results show that the CL3 strain grew 44% slower than its parental strain under nonaerated (fermentative) conditions due to the inactivation of the main acetyl-CoA production pathway. In contrast to E. coli B and W3110 pflB derivatives, we found that the MG1655 pflB derivative is able to grow in mineral media with glucose as the sole carbon source under fermentative conditions. The glycolytic flux was 2.8-fold higher in CL3 when compared to the wild-type strain, and lactate yield on glucose was 95%. Although a low cell mass formed under fermentative conditions with this strain (1.2 g/L), the volumetric productivity of CL3 was 1.31 g/L h. In comparison with the parental strain, CL3 has a 22% lower ATP/ADP ratio. In contrast to wild-type E. coli, the ATP yield from glucose to lactate is 2 ATP/glucose, so CL3 has to improve its glycolytic flux in order to fulfill its ATP needs in order to grow. The aceF deletion in strains MG1655 and CL3 indicates that the pyruvate dehydrogenase (PDH) complex is functional under glucose-fermentative conditions. These results suggest that the pyruvate to acetyl-CoA flux in CL3 is dependent on PDH activity and that the decrease in the ATP/ADP ratio causes an increase in the flux of glucose to lactate.

Specific ethanol production rate in ethanologenic Escherichia coli strain KO11 Is limited by pyruvate decarboxylase

Modification of ethanol productivity and yield, using mineral medium supplemented with glucose or xylose as carbon sources, was studied in ethanologenic Escherichia coli KO11 by increasing the activity of five key carbon metabolism enzymes. KO11 efficiently converted glucose or xylose to ethanol with a yield close to 100% of the theoretical maximum when growing in rich medium. However, when KO11 ferments glucose or xylose in mineral medium, the ethanol yields decreased to only 70 and 60%, respectively. An increase in GALP(Ec) (permease of galactose-glucose-xylose) or PGK(Ec) (phosphoglycerate kinase) activities did not change xylose or glucose and ethanol flux. However, when PDC(Zm) (pyruvate decarboxylase from Zymomonas mobilis) activity was increased 7-fold, the yields of ethanol from glucose or xylose were increased to 85 and 75%, respectively, and organic acid formation rates were reduced. Furthermore, as a response to a reduction in acetate and ATP yield, and a limited PDC(Zm) activity, an increase in PFK(Ec) (phosphofructokinase) or PYK(Bs) (pyruvate kinase from Bacillus stearothermophilus) activity drastically reduced glucose or xylose consumption and ethanol formation flux. This experimental metabolic control analysis showed that ethanol flux in KO11 is negatively controlled by phosphofructokinase and pyruvate kinase, and positively influenced by the PDC(Zm) activity level.

Abdominal mass: "fetus in fetu"

A female newborn presented a mass in the left upper abdominal quadrant. It was removed by surgery and contained two independent fetuses. Dissection and radiological study of the fetuses showed an axial skeleton and long bones. It corresponds to the generally recognized diagnostic criteria of fetus in fetu.

Partial splenic embolization in hypersplenism

Four patients with portal hypertension, oesophageal varices and severe hypersplenism were treated by partial splenic embolization. All showed improvement of blood and platelet counts early in the postoperative period. Three months after embolization IgA and C3 levels increased significantly. All patients had a decrease in the incidence of variceal bleeding and this procedure provides an acceptable alternative to splenectomy.

[Intestinal malrotation in children]

Intestinal malrotation has received, so far, little attention in the Spanish medical literature. This is probably due to the fact that is variable forms of clinical presentation may be overlooked during infancy and childhood and be present or not later in adult life. This is a report on 33 patients between 1 week and 8 years old operated upon, from 1965 to 1985, at the Clinica Infantil "La Paz", Madrid, with pre or postoperative diagnoses of intestinal malrotation (patients with Bochdalek's hernia, omphalocele and gastrosschisis are excluded). Midgut volvulus has been the most frequent preoperative complication and has occurred in 50% of patients. Intestinal obstruction was the most frequent clinical presentation, specially in patients under one week of age. There was a 30% figure of associated malformations, mostly of the duodenojejunal area (atresia, diaphragm, anular pancreas). All 5 deceased patients had other associated malformations. Long term survival was 85%.

[Pathogenic factors and therapeutic criteria in 82 newborn infants with necrotizing enterocolitis]

Sixty newborn infants with necrotizing enterocolitis (NEC) were retrospectively studied in 1979. The incidence was 0,49/1.000 living newborns: 81% were under 2,500 g and 30% under 1.500 g. We found a very low incidence of the so-called pathogenic factors. Feeding started in this group on the 24 h of life, with adapted formulas; 28% underwent surgery with a postoperative mortality of 62% and an overall mortality of 28%. Ten out of the 17 deceased were under 1.500 g. From 1979 with a similar medical treatment we introduced a prospective study consisting of a protocol of 10 different parameters including clinical, radiological and analytical values, the aim being a more objective way of indicating when to operate the patient. Special meticulous care of the nutrition of the low-weight babies was taken; 22 patients were treated til 1982, only 4,5% were under 1.500 g. The initial feeding time in all high risk babies under 1.250 g being 7 days with gastric gavage and elementary diets. All the infants with more than 60% values in the protocol underwent surgery (38%). The postoperative mortality was 37% with an overall mortality of 19%. A look back to our series suggests a clear usefulness of the protocol and the suspicion that the delay on feeding with intragastric continuous perfusion in low weight babies reduces NEC.

[Leydig cell tumor with pseudoprecocious puberty (author's transl)]

Authors present a case of a Leydig cell testicular tumor in a boy aged three years with a six-month follow-up. This type of tumor which is usually hormone-producing has in children a virilizing effect giving signs of pseudoprecocious puberty. Hormonal tests before and after surgery are described as well as the histological study. The various possibilities of differential diagnosis, treatment and prognosis in the presence of a unilateral testis enlargement in a boy are commented.