How much territory can a single E. coli cell control?

Rapid Concentration and Detection of Bacteria in Milk Using a Microfluidic Surface Acoustic Wave Activated Nanosieve

Rapid detection of microbes is a key feature for monitoring food quality. Unfortunately, current detection systems rely on labor-intensive and time-consuming lab-based processes that are not suitable for point-of-interest applications and typically require several days before results are available. Here, we demonstrate a microfluidic system capable of rapidly concentrating, fluorescent staining, and detecting bacteria in unprocessed complex biological media such as milk. This concentration is done using a surface acoustic wave-driven microfluidic device which operates based on the Bjerknes force, a force generated on one particle by another in its close proximity. We exploit this effect by exciting a tightly packed bed of 50 μm polystyrene microparticles temporarily with surface acoustic waves within a microfluidic device to capture and release bacterial cells on demand. The bacterial cells are fluorescently stained during capture and then detected using fluorescence microscopy upon release. This device offers a high capturing efficiency (>80%) and a 34 Colony Forming Units (CFU)/mL limit of detection, which is 1 order of magnitude below that of plate counting at 30 CFU per standard 100 μL plate (or 300 CFU/mL). This can be attained in just 1 h of processing at 10 μL/min. With this system, we demonstrate that bacterial detection from extremely low concentration samples down to the order of ∼10 CFU/mL is possible without requiring any additional external pre- or postprocessing.

Review on the Significant Interactions between Ultrafine Gas Bubbles and Biological Systems

Having sizes comparable with living cells and high abundance, ultrafine bubbles (UBs) are prone to inevitable interactions with different types of cells and facilitate alterations in physiological properties. The interactions of four typical cell types (e.g., bacterial, fungal, plant, and mammalian cells) with UBs have been studied over recent years. For bacterial cells, UBs have been utilized in creating the capillary force to tear down biofilms. The release of high amounts of heat, pressure, and free radicals during bubble rupture is also found to affect bacterial cell growth. Similarly, the bubble gas core identity plays an important role in the development of fungal cells. By the proposed mechanism of attachment of UBs on hydrophobin proteins in the fungal cell wall, oxygen and ozone gas-filled ultrafine bubbles can either promote or hinder the cell growth rate. On the other hand, reactive oxygen species (ROS) formation and mass transfer facilitation are two means of indirect interactions between UBs and plant cells. Likewise, the use of different gas cores in generating bubbles can produce different physical effects on these cells, for example, hydrogen gas for antioxidation against infections and oxygen for oxidation of toxic metal ions. For mammalian cells, the importance of investigating their interactions with UBs lies in the bubbles' action on cell viability as membrane poration for drug delivery can greatly affect cells' survival. UBs have been utilized and tested in forming the pores by different methods, ranging from bubble oscillation and microstream generation through acoustic cavitation to bubble implosion.

Enhanced Escherichia coli removal from stormwater with bermudagrass-derived activated biochar filtration systems

Stormwater treatment and reuse can alleviate water pollution and scarcity while current sand filtration systems showed low treatment performance for stormwater. For enhancing E. coli removal in stormwater, this study applied the bermudagrass-derived activated biochars (BCs) in the BC-sand filtration systems for E. coli removal. Compared with the pristine BC (without activation), the FeCl3 and NaOH activations increased the BC carbon content from 68.02% to 71.60% and 81.22% while E. coli removal efficiency increased from 77.60% to 81.16% and 98.68%, respectively. In all BCs, the BC carbon content showed a highly positive correlation with E. coli removal efficiency. The FeCl3 and NaOH activations also led to the enhancement of roughness of BC surface for enhancing E. coli removal by straining (physical entrapment). The main mechanisms for E. coli removal by BC-amended sand column were found to be hydrophobic attraction and straining. Additionally, under 105-107 CFU/mL of E. coli, final E. coli concentration in NaOH activated BC (NaOH-BC) column was one order of magnitude lower than those in pristine BC and FeCl3 activated BC (Fe-BC) columns. The presence of humic acid remarkably lowered the E. coli removal efficiency from 77.60% to 45.38% in pristine BC-amended sand column while slightly lowering the E. coli removal efficiencies from 81.16% and 98.68% to 68.65% and 92.57% in Fe-BC and NaOH-BC-amended sand columns, respectively. Moreover, compared to pristine BC, the activated BCs (Fe-BC and NaOH-BC) also resulted in the lower antibiotics (tetracycline and sulfamethoxazole) concentrations in the effluents from the BC-amended sand columns. Therefore, for the first time, this study indicated NaOH-BC showed high potential for effective treatment of E. coli from stormwater by the BC-amended sand filtration system compared with pristine BC and Fe-BC.

Enterobacteria Survival, Percolation, and Leaching on Soil Fertilized with Swine Manure

Swine manure has a high load of pathogens, which can pose a risk to human and environmental health. In Brazil, studies evaluating the survival of pathogens in soil are scarce. Therefore, this study aimed to evaluate the survival, percolation, and leaching of enterobacteria in clayey soil after fertilization with swine manure. For this purpose, soil columns were fertilized with manure spiked with enterobacteria. The microorganisms' behavior was monitored in terms of survival, percolation, and leaching with and without rain. Soil samples were collected, and Escherichia coli and Salmonella enterica serovar Senftemberg were quantified. The results indicated that E. coli survived for a longer period (43 days) than S. senftemberg (14 days). E. coli percolated quickly through the soil, leaching 60 cm in less than 5 min during rainy events and remaining viable for up to 24 h after the rain. The results show the importance of treating manure effectively before being added to the soil. An efficient treatment could be anaerobic digestion, followed by a pond system. Considering the characteristics of swine-producing regions, the load of effluents applied to the soil may percolate, leach, or run off and consequently contaminate water bodies with pathogens.

Combating Escherichia coli O157:H7 with Functionalized Chickpea-Derived Antimicrobial Peptides

The rapid dissemination of antibiotic resistance accelerates the desire for new antibacterial agents. Here, a class of antimicrobial peptides (AMPs) is designed by modifying the structural parameters of a natural chickpea-derived AMP-Leg2, termed "functionalized chickpea-derived Leg2 antimicrobial peptides" (FCLAPs). Among the FCLAPs, KTA and KTR show superior antibacterial efficacy against the foodborne pathogen Escherichia coli (E. coli) O157:H7 (with MICs in the range of 2.5-4.7 µmol L^-1 ) and demonstrate satisfactory feasibility in alleviating E. coli O157:H7-induced intestinal infection. Additionally, the low cytotoxicity along with insusceptibility to antimicrobial resistance increases the potential of FCLAPs as appealing antimicrobials. Combining the multi-omics profiling andpeptide-membrane interaction assays, a unique dual-targeting mode of action is characterized. To specify the antibacterial mechanism, microscopical observations, membrane-related physicochemical properties studies, and mass spectrometry assays are further performed. Data indicate that KTA and KTR induce membrane damage by initially targeting the lipopolysaccharide (LPS), thus promoting the peptides to traverse the outer membrane. Subsequently, the peptides intercalate into the peptidoglycan (PGN) layer, blocking its synthesis, and causing a collapse of membrane structure. These findings altogether imply the great potential of KTA and KTR as promising antibacterial candidates in combating the growing threat of E. coli O157:H7.

Controlled Iodine Phase Transfer of Covalent Organic Framework Membranes for Instant but Sustained Disinfection

Freestanding membranes of CuCl₂-implanted TpPa covalent organic frameworks (COFs) were mechanochemically produced. The resulting membrane had a high I₂ adsorption capacity (566.78 g·mol^-1) in cyclohexane, which corresponds to 2.2I₂ per unit cell with 1.3I₂ immobilized on 3Cl^- ions (60%) and 0.9 on 3N atoms (40%). Upon being placed in aqueous media, the membrane released 61.1% of its loaded I₂ mainly by its Cl^- ions within 10 min and the remaining 38.9% mainly from its N atoms within about 5 h. Thanks to that, the COF membranes loaded with 1.5 mg of I₂ could be repetitively utilized to kill about 10⁸ CFU/mL E. coli in 0.5-3 min at least five times, after which the membranes could retain their bactericidal activity for 4 h against 10⁸ CFU/mL E. coli. This highlights the promising application of I₂-loaded TpPa-CuCl₂ COF membranes for instant and sustained disinfection.

Surface modification of magnetic nanoparticles by bacteriophages and ionic liquids precursors

Magnetic nanoparticles (MNPs) have recently been a point of interest for many researchers due to their properties. However, the studies on the influence of bacteriophages on the synthesis of MNPs seem to be lacking. Furthermore, bacteriophage-modified MNPs have not been combined with n-alkyl quaternary ammonium ionic liquid precursors (QAS). In this study, the aim was to assess the influence of two distinctly different bacteriophages (Escherichia phage P1 and Pseudomonas phage Φ6) on MNPs synthesis in the presence or absence of QAS. Synthesized MNPs have been characterized with X-ray diffraction (XRD) and Mössbauer spectroscopy in terms of changes in the crystallographic structure; scanning electron microscopy (SEM) for changes in the morphology; and ζ-potential. Moreover, the sorption parameters and the loss of viability of bacteria that interacted with MNPs have been determined. The sorption of bacteria differs significantly among the tested samples. Furthermore, the viability of the bacteria adsorbed on MNPs varies in the presence of QAS, depending on the length of the n-alkyl chain. The study has revealed that MNPs can be bound with bacteriophages. Mössbauer spectroscopy has also revealed the probable influence of bacteriophages on the formation of crystals. However, these phenomena require further studies.

The chemical neighborhood of cells in a diffusion-limited system

Microorganisms follow us everywhere, and they will be essential to sustaining long-term human space exploration through applications such as vitamin synthesis, biomining, and more. Establishing a sustainable presence in space therefore requires that we better understand how stress due to the altered physical conditions of spaceflight affects our companion organisms. In microgravity environments such as orbital space stations, microorganisms likely experience the change in gravity primarily through changes in fluid mixing processes. Without sedimentation and density-driven convection, diffusion becomes the primary process governing the movement of growth substrates and wastes for microbial cells in suspension culture. Non-motile cells might therefore develop a substrate-deficient "zone of depletion" and experience stress due to starvation and/or waste build-up. This would in turn impact the concentration-dependent uptake rate of growth substrates and could be the cause of the altered growth rates previously observed in microorganisms in spaceflight and in ground-simulated microgravity. To better understand the extent of these concentration differences and their potential influence on substrate uptake rates, we used both an analytical solution and finite difference method to visualize concentration fields around individual cells. We modeled diffusion, using Fick's Second Law, and nutrient uptake, using Michaelis-Menten kinetics, and assessed how that distribution varies in systems with multiple cells and varied geometries. We determined the radius of the zone of depletion, within which cells had reduced the substrate concentration by 10%, to be 5.04 mm for an individual Escherichia coli cell in the conditions we simulated. However, we saw a synergistic effect with multiple cells near each other: multiple cells in close proximity decreased the surrounding concentration by almost 95% from the initial substrate concentration. Our calculations provide researchers an inside look at suspension culture behavior in the diffusion-limited environment of microgravity at the scale of individual cells.

Does Secondary Plant Metabolite Ursolic Acid Exhibit Antibacterial Activity against Uropathogenic Escherichia coli Living in Single- and Multispecies Biofilms?

Multispecies bacterial biofilms are the often cause of chronic recurrent urinary tract infections within the human population. Eradicating such a complex bacterial consortium with standard pharmacotherapy is often unsuccessful. Therefore, plant-derived compounds are currently being researched as an alternative strategy to antibiotic therapy for preventing bacterial biofilm formation and facilitating its eradication. Therefore, our research aimed to determine the effect of secondary plant metabolite ursolic acid (UA) on the growth and survival, the quantity of exopolysaccharides formed, metabolic activity, and morphology of uropathogenic Gram-negative rods living in single- and mixed-species biofilms at various stages of their development. Spectrophotometric methods were used for biofilm mass formation and metabolic activity determination. The survival of bacteria was established using the serial dilution assay. The decrease in survival and inhibition of biofilm creation, both single- and multispecies, as well as changes in the morphology of bacterial cells were noticed. As UA exhibited better activity against young biofilms, the use of UA-containing formulations, especially during the initial steps of urinary tract infection, seems to be reasonable. However, the future direction should be a thorough understanding of the mechanisms of UA activity as a bioactive substance.

Patatin-like phospholipase CapV in Escherichia coli - morphological and physiological effects of one amino acid substitution

In rod-shaped bacteria, morphological plasticity occurs in response to stress, which blocks cell division to promote filamentation. We demonstrate here that overexpression of the patatin-like phospholipase variant CapV_Q329R, but not CapV, causes pronounced sulA-independent pyridoxine-inhibited cell filamentation in the Escherichia coli K-12-derivative MG1655 associated with restriction of flagella production and swimming motility. Conserved amino acids in canonical patatin-like phospholipase A motifs, but not the nucleophilic serine, are required to mediate CapV_Q329R phenotypes. Furthermore, CapV_Q329R production substantially alters the lipidome and colony morphotype including rdar biofilm formation with modulation of the production of the biofilm activator CsgD, and affects additional bacterial traits such as the efficiency of phage infection and antimicrobial susceptibility. Moreover, genetically diverse commensal and pathogenic E. coli strains and Salmonella typhimurium responded with cell filamentation and modulation in colony morphotype formation to CapV_Q329R expression. In conclusion, this work identifies the CapV variant CapV_Q329R as a pleiotropic regulator, emphasizes a scaffold function for patatin-like phospholipases, and highlights the impact of the substitution of a single conserved amino acid for protein functionality and alteration of host physiology.

Are Uropathogenic Bacteria Living in Multispecies Biofilm Susceptible to Active Plant Ingredient-Asiatic Acid?

Urinary tract infections (UTIs) are a serious health problem in the human population due to their chronic and recurrent nature. Bacteria causing UTIs form multispecies biofilms being resistant to the activity of the conventionally used antibiotics. Therefore, compounds of plant origin are currently being searched for, which could constitute an alternative strategy to antibiotic therapy. Our study aimed to determine the activity of asiatic acid (AA) against biofilms formed by uropathogenic Escherichia coli, Enterobacter cloacae, and Pseudomonas aeruginosa. The influence of AA on the survival, biofilm mass formation by bacteria living in mono-, dual-, and triple-species consortia as well as the metabolic activity and bacterial cell morphology were determined. The spectrophotometric methods were used for biofilm mass synthesis and metabolic activity determination. The survival of bacteria was established using the serial dilution assay. The decrease in survival and a weakening of the ability to create biofilms, both single and multi-species, as well as changes in the morphology of bacterial cells were noticed. As AA works best against young biofilms, the use of AA-containing formulations, especially during the initial stages of infection, seems to be reasonable. However, there is a need for further research concerning AA especially regarding its antibacterial mechanisms of action.

Stochastic nucleoid segregation dynamics as a source of the phenotypic variability in E. coli

Segregation of the replicating chromosome from a single to two nucleoid bodies is one of the major processes in growing bacterial cells. The segregation dynamics is tuned by intricate interactions with other cellular processes such as growth and division, ensuring flexibility in a changing environment. We hypothesize that the internal stochasticity of the segregation process may be the source of cell-to-cell phenotypic variability, in addition to the well-established gene expression noise and uneven partitioning of low copy number components. We compare dividing cell lineages with filamentous cells, where the lack of the diffusion barriers is expected to reduce the impact of other factors on the variability of nucleoid segregation dynamics. The nucleoid segregation was monitored using time-lapse microscopy in live E. coli cells grown in linear grooves. The main characteristics of the segregation process, namely, the synchrony of partitioning, rates of separation, and final positions, as well as the variability of these characteristics, were determined for dividing and filamentous lineages growing under the same conditions. Indeed, the gene expression noise was considerably homogenized along filaments as determined from the distribution of CFP and YFP stochastically expressed from the chromosome. We find that 1) the synchrony of nucleoid partitioning is progressively decreasing during consecutive cell cycles, but to a significantly lesser degree in filamentous than in dividing cells; 2) the mean partitioning rate of nucleoids is essentially the same in dividing and filamentous cells, displaying a substantial variability in both; and 3) nucleoids segregate to the same distances in dividing and filamentous cells. Variability in distances is increasing during successive cell cycles, but to a much lesser extent in filamentous cells. Our findings indicate that the variability of the chromosome segregation dynamics is reduced upon removal of boundaries between nucleoids, whereas the remaining variability is essentially inherent to the nucleoid itself.

Transgenesis of mammalian PABP reveals mRNA polyadenylation as a general stress response mechanism in bacteria

In eukaryotes, mRNA 3′-polyadenylation triggers poly(A) binding protein (PABP) recruitment and stabilization. In a stark contrast, polyadenylation marks mRNAs for degradation in bacteria. To study this difference, we trans-express the mammalian nuclear PABPN1 chromosomally and extra-chromosomally in Escherichia coli. Expression of PABPN1 but not the mutant PABPN1 stabilizes polyadenylated mRNAs and improves their half-lives. In the presence of PABPN1, 3′-exonuclease PNPase is not detected on PA-tailed mRNAs compromising the degradation. We show that PABPN1 trans-expression phenocopies pcnB (that encodes poly(A) polymerase, PAPI) mutation and regulates plasmid copy number. Genome-wide RNA-seq analysis shows a general up-regulation of polyadenylated mRNAs on PABPN1 expression, the largest subset of which are those involved in general stress response. However, major global stress regulators are unaffected on PABPN1 expression. Concomitantly, PABPN1 expression or pcnB mutation imparts cellular tolerance to multiple stresses. This study establishes mRNA 3′-polyadenylation as a general stress response mechanism in E. coli.

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Trans expression of mammalian PABPN1 stabilizes polyadenyated mRNAs in E. coli

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PABPN1 expression phenocopies pcnB mutation and regulates plasmid copy number

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3′-polyadenylation acts as a general stress response mechanism in bacteria

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This study indicates an evolutionary significance of PABP in mRNA metabolism

Sarconesin II, a New Antimicrobial Peptide Isolated from Sarconesiopsis magellanica Excretions and Secretions

Antibiotic resistance is at dangerous levels and increasing worldwide. The search for new antimicrobial drugs to counteract this problem is a priority for health institutions and organizations, both globally and in individual countries. Sarconesiopsis magellanica blowfly larval excretions and secretions (ES) are an important source for isolating antimicrobial peptides (AMPs). This study aims to identify and characterize a new S. magellanica AMP. RP-HPLC was used to fractionate ES, using C18 columns, and their antimicrobial activity was evaluated. The peptide sequence of the fraction collected at 43.7 min was determined by mass spectrometry (MS). Fluorescence and electronic microscopy were used to evaluate the mechanism of action. Toxicity was tested on HeLa cells and human erythrocytes; physicochemical properties were evaluated. The molecule in the ES was characterized as sarconesin II and it showed activity against Gram-negative (Escherichia coli MG1655, Pseudomonas aeruginosa ATCC 27853, P. aeruginosa PA14) and Gram-positive (Staphylococcus aureus ATCC 29213, Micrococcus luteus A270) bacteria. The lowest minimum inhibitory concentration obtained was 1.9 μM for M. luteus A270; the AMP had no toxicity in any cells tested here and its action in bacterial membrane and DNA was confirmed. Sarconesin II was documented as a conserved domain of the ATP synthase protein belonging to the Fli-1 superfamily. The data reported here indicated that peptides could be alternative therapeutic candidates for use in infections against Gram-negative and Gram-positive bacteria and eventually as a new resource of compounds for combating multidrug-resistant bacteria.

Phage-Antibiotic Synergy via Delayed Lysis

When phages infect bacteria cultured in the presence of sublethal doses of antibiotics, the sizes of the phage plaques are significantly increased. This phenomenon is known as phage-antibiotic synergy (PAS). In this study, the observation of PAS was extended to a wide variety of bacterium-phage pairs using different classes of antibiotics. PAS was shown in both Gram-positive and Gram-negative bacteria. Cells stressed with β-lactam antibiotics filamented or swelled extensively, resulting in an increase in phage production. PAS was also sometimes observed in the presence of other classes of antibiotics with or without bacterial filamentation. The addition of antibiotics induced recA expression in various bacteria, but a recA deletion mutant strain of Escherichia coli also showed filamentation and PAS in the presence of quinolone antibiotics. The phage adsorption efficiency did not change in the presence of the antibiotics when the cell surfaces were enlarged as they filamented. Increases in the production of phage DNA and mRNAs encoding phage proteins were observed in these cells, with only a limited increase in protein production. The data suggest that PAS is the product of a prolonged period of particle assembly due to delayed lysis. The increase in the cell surface area far exceeded the increase in phage holin production in the filamented host cells, leading to a relatively limited availability of intracellular holins for aggregating and forming holes in the host membrane. Reactive oxygen species (ROS) stress also led to an increased production of phages, while heat stress resulted in only a limited increase in phage production.IMPORTANCE Phage-antibiotic synergy (PAS) has been reported for a decade, but the underlying mechanism has never been vigorously investigated. This study shows the presence of PAS from a variety of phage-bacterium-antibiotic pairings. We show that increased phage production resulted directly from a lysis delay caused by the relative shortage of holin in filamented bacterial hosts in the presence of sublethal concentrations of stress-inducing substances, such as antibiotics and reactive oxygen species (ROS).

Evaluation of membrane fluidity of multidrug-resistant isolates of Escherichia coli and Staphylococcus aureus in presence and absence of antibiotics

In the face of the serious problem of antimicrobial resistance and the global dissemination of multidrug-resistant (MDR) bacteria, it is relevant to deeply study such bacteria both genetically and phenotypically. It is well known that bacteria have the ability to modify the biophysical properties of their cytoplasmic membranes, namely fluidity, in order to survive and thrive in hostile environments. The aim of this study was to assess and compare the membrane fluidity among multidrug-resistant (MDR) isolates of Escherichia coli and Staphylococcus aureus in absence and in presence of antibiotics (ceftazidime or ciprofloxacin). The membrane fluidity was monitored at 24-h intervals up to three days and at the sixth day, by measuring the anisotropy of 1,6-diphenyl-1,3,5-hexatriene (DPH) and the generalized polarization (GP) of Laurdan (6-dodecanoyl-2-dimethylaminonaphthalene). The anisotropy values as well as the Laurdan excitation GP (GP_exc) values obtained from all three E. coli strains (two MDR isolates and one susceptible reference strain) were quite similar and indicative of a very alike membrane phospholipid composition, regardless harboring or not resistance to multiple antimicrobials. Nonetheless, in the case of S. aureus, the anisotropy values were more increased in methicillin-resistant S. aureus (MRSA) isolates in comparison to the reference strain, meaning they have a less fluid membrane. Equally, GP_exc values were statistically different among the three S. aureus strains and showed that the two MRSA isolates had more rigid membranes than the susceptible strain. The exposition of MDR isolates of S. aureus to subinhibitory concentrations of ciprofloxacin did not affect neither the anisotropy values nor the GP_exc values, therefore, not altering membrane fluidity. Membrane integrity, assessed by the Live/Dead staining, of all strains and conditions studied was maintained over the six days. Thus, these preliminary studies on membrane properties of MDR isolates demonstrate that i) MRSA seem to have a more rigid membrane that susceptible S. aureus and ii) the presence of subinhibitory concentrations of antibiotics does not significantly alter the membrane fluidity of S. aureus, regardless being MDR or susceptible, but slightly affect the membrane fluidity of E. coli.

CbtA toxin of Escherichia coli inhibits cell division and cell elongation via direct and independent interactions with FtsZ and MreB

The toxin components of toxin-antitoxin modules, found in bacterial plasmids, phages, and chromosomes, typically target a single macromolecule to interfere with an essential cellular process. An apparent exception is the chromosomally encoded toxin component of the E. coli CbtA/CbeA toxin-antitoxin module, which can inhibit both cell division and cell elongation. A small protein of only 124 amino acids, CbtA, was previously proposed to interact with both FtsZ, a tubulin homolog that is essential for cell division, and MreB, an actin homolog that is essential for cell elongation. However, whether or not the toxic effects of CbtA are due to direct interactions with these predicted targets is not known. Here, we genetically separate the effects of CbtA on cell elongation and cell division, showing that CbtA interacts directly and independently with FtsZ and MreB. Using complementary genetic approaches, we identify the functionally relevant target surfaces on FtsZ and MreB, revealing that in both cases, CbtA binds to surfaces involved in essential cytoskeletal filament architecture. We show further that each interaction contributes independently to CbtA-mediated toxicity and that disruption of both interactions is required to alleviate the observed toxicity. Although several other protein modulators are known to target FtsZ, the CbtA-interacting surface we identify represents a novel inhibitory target. Our findings establish CbtA as a dual function toxin that inhibits both cell division and cell elongation via direct and independent interactions with FtsZ and MreB.

Bacterially encoded toxin-antitoxin systems, which consist of a small toxin protein that is co-produced with a neutralizing antitoxin, are a potential avenue for the identification of novel antibiotic targets. These toxins typically target essential cellular processes, causing growth arrest or cell death when unchecked by the antitoxin. Our study is focused on the CbtA toxin of E. coli, which was known to inhibit both bacterial cell division and also bacterial cell elongation (the process by which rod-shaped bacteria grow prior to cell division). We report that the effects of CbtA on cell division and cell elongation are genetically separable, and that they are due to direct and independent interactions with its targets FtsZ and MreB, essential cytoskeletal proteins that direct cell division and cell elongation, respectively. Our genetic analysis defines the functionally relevant target surfaces on FtsZ and MreB; in the case of FtsZ this surface represents a novel inhibitory target. As a dual-function toxin that independently targets two essential cytoskeletal elements, CbtA could guide the design of dual-function antibiotics whose ability to independently target more than one essential cellular process might impede the development of drug resistance, which is a growing public health threat.

Optical biosensors for bacteria detection by a peptidomimetic antimicrobial compound

In this work we present a label-free optical biosensor for rapid bacteria detection using a novel peptide-mimetic compound, as the recognition element. The biosensor design is based on an oxidized porous silicon (PSiO2) nanostructure used as the optical transducer, functionalized with the sequence K-[C12K]7 (referred to as K-7α12), which is a synthetic antimicrobial peptide. This compound is a member of a family of oligomers of acylated lysines (OAKs), mimicking the hydrophobicity and charge of natural antimicrobial peptides. The OAK is tethered to the PSiO2 film and the changes in the reflectivity spectrum are monitored upon exposure to Escherichia coli (E. coli) bacterial suspensions and their lysates. We show that capture of bacterial cell fragments induces predictable changes in the reflectivity spectrum, proportional to E. coli concentrations, thereby enabling rapid, sensitive and reproducible detection of E. coli at concentrations as low as 10(3) cells per mL. While for intact bacterial cells, the K-7α12-tethered PSiO2 shows a poor capturing ability, resulting in an insignificant optical response. The biosensor performance is also studied upon exposure to model Gram positive and negative bacterial lysates, suggesting preferential capture of E. coli cell fragments in the presented scheme. These OAK-based biosensors offer significant advantages in comparison with conventional antibody-based assays, in terms of their simple and cost-effective production, while providing numerous possible sequence combinations for designing new detection schemes.