Conversion of Agroindustrial Wastes to Rhamnolipid by Enterobacter sp. UJS-RC and Its Role against Biofilm-Forming Foodborne Pathogens

Rhamnolipid is the main group of biosurfactants predominantly produced by Pseudomonas aeruginosa, a ubiquitous and opportunistic pathogen, which limits its large-scale exploitation. Thus, cost-effective rhamnolipid production from a newly isolated nonpathogenic Enterobacter sp. UJS-RC was investigated. The highest rhamnolipid production (4.4 ± 0.2 g/L) was achieved in a medium constituting agroindustrial wastes (sugarcane molasses and corn steep liquor) as substrates. Rhamnolipid exhibited reduced surface tension to 72-28 mN/m with an emulsification index of 75%. The structural analyses demonstrated the presence of methoxyl, carboxyl, and hydroxyl groups in rhamnolipid. Mass spectra indicated eight rhamnolipid congeners, where dirhamnolipid (m/z 650.01) was the dominant congener. Rhamnolipid inhibited biofilm formation of Staphylococcus aureus in a dose-dependent manner, supported by scanning electron microscopy disclosing the disruption of the microcolony/exopolysaccharide matrix. Rhamnolipid's ability to generate reactive oxygen species has thrown light on the mechanism through which the killing of test bacteria may occur.

Cloning and characterization of short-chain N-acyl homoserine lactone-producing Enterobacter asburiae strain L1 from lettuce leaves

In gram-negative bacteria, bacterial communication or quorum sensing (QS) is achieved using common signaling molecules known as N-acyl homoserine lactones (AHL). We have previously reported the genome of AHL-producing bacterium, Enterobacter asburiae strain L1. In silico analysis of the strain L1 genome revealed the presence of a pair of luxI/R genes responsible for AHL-type QS, designated as easIR. In this work, the 639 bp luxI homolog, encoding 212 amino acids, have been cloned and overexpressed in Escherichia coli BL21 (DE3)pLysS. The purified protein (~25 kDa) shares high similarity to several members of the LuxI family among different E asburiae strains. Our findings showed that the heterologously expressed EasI protein has activated violacein production by AHL biosensor Chromobacterium violaceum CV026 as the wild-type E. asburiae. The mass spectrometry analysis showed the production of N-butanoyl homoserine lactone and N-hexanoyl homoserine lactone from induced E. coli harboring the recombinant EasI, suggesting that EasI is a functional AHL synthase. E. asburiae strain L1 was also shown to possess biofilm-forming characteristic activity using crystal violet binding assay. This is the first report on cloning and characterization of the luxI homolog from E. asburiae.

Coliform Bacteria for Bioremediation of Waste Hydrocarbons

Raw, domestic sewage of Kuwait City contained about 106 ml-1 colony forming units of Enterobacter hormaechei subsp. oharae (56.6%), Klebsiella spp. (36%), and Escherichia coli (7.4%), as characterized by their 16S rRNA-gene sequences. The isolated coliforms grew successfully on a mineral medium with crude oil vapor as a sole source of carbon and energy. Those strains also grew, albeit to different degrees, on individual n-alkanes with carbon chains between C9 and C36 and on the individual aromatic hydrocarbons, toluene, naphthalene, phenanthrene, and biphenyl as sole sources of carbon and energy. These results imply that coliforms, like other hydrocarbonoclastic microorganisms, oxidize hydrocarbons to the corresponding alcohols and then to aldehydes and fatty acids which are biodegraded by β-oxidation to acetyl CoA. The latter is a well-known key intermediate in cell material and energy production. E. coli cells grown in the presence of n-hexadecane (but not in its absence) exhibited typical intracellular hydrocarbon inclusions, as revealed by transmission electron microscopy. Raw sewage samples amended with crude oil, n-hexadecane, or phenanthrene lost these hydrocarbons gradually with time. Meanwhile, the numbers of total and individual coliforms, particularly Enterobacter, increased. It was concluded that coliform bacteria in domestic sewage, probably in other environmental materials too, are effective hydrocarbon-biodegrading microorganisms.

Production of FucoPol by Enterobacter A47 using waste tomato paste by-product as sole carbon source

Out-of-specification tomato paste, a by-product from the tomato processing industry, was used as the sole substrate for cultivation of the bacterium Enterobacter A47 and production of FucoPol, a value-added fucose-rich extracellular polysaccharide. Among the different tested fed-batch strategies, pH-stat, DO-stat and continuous substrate feeding, the highest production (8.77gL^-1) and overall volumetric productivity (2.92gL^-1d^-1) were obtained with continuous substrate feeding at a constant flow rate of 11gh^-1. The polymer produced had the typical FucoPol composition (37mol% fucose, 27mol% galactose, 23mol% glucose and 12mol% glucuronic acid, with an acyl groups content of 13wt%). The average molecular weight was 4.4×10⁶Da and the polydispersity index was 1.2. This study demonstrated that out-of-specification tomato paste is a suitable low-cost substrate for the production of FucoPol, thus providing a route for the valorization of this by-product into a high-value microbial product.

Enterobacter tabaci sp. nov., a novel member of the genus Enterobacter isolated from a tobacco stem

A Gram-stain negative, motile, rod-shaped bacterium, designated strain YIM Hb-3(T), was isolated from the stem of a tobacco plant. The strain was observed to form convex, circular and yellow-colored colonies. The predominant respiratory quinone was identified as Q-8. The major fatty acids (>5%) detected were C(16:1)ω7c and/or C(16:1)ω6c (summed feature 3), C(16:0), C(17:0)cyclo, C(18:1)ω7c and/or C(18:1)ω6c (summed feature 8), C(14:0)3-OH and/or iso-C(16:1)I (summed feature 2), C(14:0) and C(12:0). The genomic DNA G+C content was determined to be 54.8 mol%. Phylogenetic trees based on 16S rRNA gene sequences and multilocus sequence analysis showed that strain YIM Hb-3(T) had the closest phylogenetic relationship with Enterobacter mori LMG 25706(T). DNA-DNA relatedness value between strain YIM Hb-3(T) and E. mori LMG 25706(T) was 46.9 ± 3.8%. On the basis of phenotypic and chemotaxonomic data, phylogenetic analysis, and DNA-DNA relatedness value, strain YIM Hb-3(T) is considered to represent a novel species of the genus Enterobacter, for which the name Enterobacter tabaci sp. nov. is proposed. The type strain is YIM Hb-3(T) (=KACC 17832(T) =KCTC 42694(T)).

Study of the interactive effect of temperature and pH on exopolysaccharide production by Enterobacter A47 using multivariate statistical analysis

Enterobacter A47 synthesizes fucose-containing exopolysaccharides (EPS). Maximum EPS production (>7.00 g L(-1)) was obtained for temperature and pH within 25-35°C and 6.0-8.0, respectively. Under these conditions, the polymers contained over 30% fucose. Glucose, galactose, and glucuronic acid contents were about 28%, 25%, and 10%, respectively, and the total acyl groups content was about 20 wt.%. The average molecular weight (Mw) was around 4.0 × 10(6). Outside the optimal temperature and pH ranges, fucose, galactose and glucuronic acid, and the total acyl group contents were reduced, while the glucose content increased, new monomers (rhamnose and glucosamine) were detected, and the Mw increased to ≥ 1.10 × 10(7). This study revealed the ability of Enterobacter A47 to synthesize different heteropolysaccharides as a function of pH and temperature, a feature that can be exploited to obtain tailored polymer composition. Moreover, the production of high fucose content EPS was stable for wide pH and temperature ranges, which is important for the envisaged industrial development of the bioprocess.

Cycle inhibiting factors (CIFs) are a growing family of functional cyclomodulins present in invertebrate and mammal bacterial pathogens

The cycle inhibiting factor (Cif) produced by enteropathogenic and enterohemorrhagic Escherichia coli was the first cyclomodulin to be identified that is injected into host cells via the type III secretion machinery. Cif provokes cytopathic effects characterized by G₁ and G₂ cell cycle arrests, accumulation of the cyclin-dependent kinase inhibitors (CKIs) p21^waf1/cip1 and p27^kip1 and formation of actin stress fibres. The X-ray crystal structure of Cif revealed it to be a divergent member of a superfamily of enzymes including cysteine proteases and acetyltransferases that share a conserved catalytic triad. Here we report the discovery and characterization of four Cif homologs encoded by different pathogenic or symbiotic bacteria isolated from vertebrates or invertebrates. Cif homologs from the enterobacteria Yersinia pseudotuberculosis, Photorhabdus luminescens, Photorhabdus asymbiotica and the β-proteobacterium Burkholderia pseudomallei all induce cytopathic effects identical to those observed with Cif from pathogenic E. coli. Although these Cif homologs are remarkably divergent in primary sequence, the catalytic triad is strictly conserved and was shown to be crucial for cell cycle arrest, cytoskeleton reorganization and CKIs accumulation. These results reveal that Cif proteins form a growing family of cyclomodulins in bacteria that interact with very distinct hosts including insects, nematodes and humans.

Exploring multi-metal biosorption by indigenous metal-hyperresistant Enterobacter sp. J1 using experimental design methodologies

A novel experimental design, combining mixture design and response surface methodology (RSM), was developed to investigate the competitive adsorption behavior of lead, copper and cadmium by an indigenous isolate Enterobacter sp. J1 able to tolerate high concentrations of a variety of heavy metals. Using the proposed combinative experimental design, two different experiment designs in a ternary metal biosorption system can be integrated to a succinct experiment and the number of experimental trials was markedly reduced from 38 to 26 by reusing the mutual experimental data. Triangular contour diagrams and triangular three-dimensional surface plots were generated to describe the ternary metal biosorption equilibrium data in mixture design systems. The results show that the preference of metal sorption of Enterobacter sp. J1 decreased in the order of Pb(2+)>Cu(2+)>Cd(2+). The presence of other metals resulted in a competitive effect. The influence of the other two metals in ternary metal biosorption system can be easily determined by comparing the stray distance from the single metal biosorption. The behavior of competitive biosorption was successfully described and predicted using a combined Langmuir-Freundlich model along with new three-dimensional contour-surface plots.

Purification and characterization of NAD-dependent n-butanol dehydrogenase from solvent-tolerant n-butanol-degrading Enterobacter sp. VKGH12

The solvent-tolerant bacterium Enterobacter sp. VKGH12 is capable of utilizing n-butanol and contains an NAD+-dependent n-butanol dehydrogenase (BDH). The BDH from n-butanol-grown Enterobacter sp. was purified from a cell-free extract (soluble fraction) to near homogeneity using a 3-step procedure. The BDH was purified 15.37-fold with a recovery of only 10.51, and the molecular mass estimated to be 38 kDa. The apparent Michaelis-Menten constant (Km) for the BDH was found to be 4 mM with respect to n-butanol. The BDH also had a broad range of substrate specificity, including primary alcohols, secondary alcohols, and aromatic alcohols, and exhibited an optimal activity at pH 9.0 and 40oC. Among the metal ions studied, Mg2+ and Mn2+ had no effect, whereas Cu2+, Zn2+, and Fe2+ at 1 mM completely inhibited the BDH activity. The BDH activity was not inhibited by PMSF, suggesting that serine is not involved in the catalytic site. The known metal ion chelator EDTA had no effect on the BDH activity. Thus, in addition to its physiological significance, some features of the enzyme, such as its activity at an alkaline pH and broad range of substrate specificity, including primary and secondary alcohols, are attractive for application to the enzymatic conversion of alcohols.

Supplementation of a novel microbial biopolymer, PGB1, from new Enterobacter sp. BL-2 delays the deterioration of type 2 diabetic mice

Antidiabetic effects of a novel microbial biopolymer (PGB)1 excreted from new Enterobacter sp. BL-2 were tested in the db/db mice. The animals were divided into normal control, rosiglitazone (0.005%, wt/wt), low PGB1 (0.1%, wt/wt), and high PGB1 (0.25%, wt/wt) groups. After 5 weeks, the blood glucose levels of high PGB1 and rosiglitazone supplemented groups were significantly lower than those of the control group. In hepatic glucose metabolic enzyme activities, the glucokinase activities of PGB1 supplemented groups were significantly higher than the control group, whereas the PEPCK activities were significantly lower. The plasma insulin and hepatic glycogen levels of the low and high PGB1 supplemented groups were significantly higher compared with the control group. Specifically, the insulin and glycogen increases were dose-responsive to PGB1 supplement. PGB1 supplement did not affect the IPGTT and IPITT compared with the control group; however, rosiglitazone significantly improved IPITT. High PGB1 and rosiglitazone supplementation preserved the appearance of islets and insulin-positive cells in immunohistochemical photographs of the pancreas compared with the control group. These results demonstrated that high PGB1 (0.25% in the diet) supplementation seemingly contributes to preventing the onset and progression of type 2 diabetes by stimulating insulin secretion and enhancing the hepatic glucose metabolic enzyme activities.

Enhanced adsorption of zinc is associated with aging and lysis of bacterial cells in batch incubations

Bacteria can immobilize significant quantities of trace metals through surface complexation reactions. However, bacterial cell lysis is an integral part of the development process, and the extent to which this process affects adsorbed metals has not been properly investigated. In order to evaluate the effects of cell lysis on metal fixation, bacterial suspensions containing approximately 10 ppm Zn in 0.01 M NaNO(3) were monitored over an one-month period for adsorbed Zn, pH, cell concentration, dissolved organic carbon, NH(3) and dissolved amino acids. Cell concentration decreased with time, in parallel with an increase in dissolved organic carbon. Zn adsorption decreased with time for suspensions with near-neutral (5.5-7.0) initial pH values, consistent with the reduction in cell concentration and/or formation of metal-ligand complexes in solution, with lysis products acting as ligands. However, Zn adsorption increased with time for suspensions with initially low pH (<or=5), and was accompanied by an upward shift in suspension pH. Surface complexation modelling suggests that enhanced adsorption of Zn is predominantly due to the increase in pH, with ternary surface complexation at pH values below the pK(a) of the carboxyl surface sites. The increase in pH is due to production of ammonia, and/or proton buffering by the amphoteric cytoplasmic compounds. The observed changes may have implications for understanding metal sequestration during remineralisation of organic matter in nature.

A medium for the presumptive detection of Enterobacter sakazakii in infant formula: interlaboratory study

A standard method for the detection of Enterobacteriaceae was modified for the presumptive detection of Enterobacter sakazakii, and the modified method was validated in an interlaboratory trial with 16 laboratories from 8 European countries. The modification included a differential-elective medium for the isolation of E. sakazakii, consisting of nutrient agar (NA) supplemented with 4-methyl-umbelliferyl alpha-D-glucoside (alpha-MUG). A 25 g sample was added to 225 mL buffered peptone water. After incubation at 35 degrees or 37 degrees C for 16 or 20 h, 10 mL nonselective enrichment was transferred into 90 mL selective enrichment. The selective enrichment was streaked on violet-red bile glucose agar (VRBGA) and incubated at 37 degrees C for 24 h. It was streaked in parallel on NA plates supplemented with alpha-MUG at 50 mg/L and incubated at 25 degrees C for 16 h, and afterwards for an additional 24 h at room temperature in the dark. E. sakazakii appeared as vivid yellow colonies under normal light and showed blue/violet fluorescence under UV light on NA + alpha-MUG plates. Validation samples represented powdered infant formula without E. sakazakii (blanks) and with low (1-10 colony-forming units [CFU]/25 g) and medium (1-10 CFU/g) contamination levels. All samples contained Pseudomonas aeruginosa and Lactobacillus spp. as background flora. The specificity for blank samples was 100%. The sensitivity of the low contamination level was similar for VRBGA and NA + alpha-MUG, i.e., 66.7% (66.7% accordance, 53.9% concordance). For the medium level the sensitivities were 96.7% (93.3% accordance, 93.5% concordance) for VRBGA and 98.3% (96.9% accordance, 96.9% concordance) for NA + alpha-MUG.

Stimulation of furanochromone accumulation in callus cultures of Ammi visnaga L. by addition of elicitors

In order to check the possibility of producing secondary metabolites, in vitro cultures of A. visnaga callus were established. The best growth of A. visnaga callus was obtained on Murashige and Skoog medium (MS) containing 6-benzyladenine (BA) and alpha-naphtaleneacetic acid (NAA). The study was concentrated on the induction of production of secondary metabolites by exposing callus to abiotic elicitors: benzo(1,2,3)-thiadiazole-7-carbothionic acid S-methyl ester (BION) and a suspension of silica (SiO2) and biotic elicitors: autoclaved lysates of Enterobacter sakazaki and scleroglucan. GC analysis indicated that not-elicited callus of A. visnaga grown in darkness accumulated 2 times more visnagin than the one which was grown under a 16-h photoperiod. The highest accumulation of visnagin was observed in the callus culture elicited with scleroglucan or BION. Scleroglucan induced also the accumulation of khellin in A. visnaga callus. The presented work shows that biosynthesis of pharmacologically important secondary metabolites in A. visnaga cultures could be stimulated by application of elicitors.

Interaction of hemoglobin with enterobacterial lipopolysaccharide and lipid A. Physicochemical characterization and biological activity

The interaction of hemoglobin (Hb) with endotoxins [i.e. with enterobacterial deep rough mutant lipopolysaccharide (LPS) Re and the "endotoxic principle" of LPS, lipid A] was investigated using a variety of physical techniques and with two biological assays, tumor necrosis factor (TNF)-alpha induction in human mononuclear cells and the Limulus amebocyte lysate (LAL) assay. Fourier-transform IR-spectroscopic experiments indicate nonelectrostatic binding to the hydrophobic moiety with a slight rigidification of the lipid A acyl chains, and an increase in the inclination of the lipid A backbone with respect to the membrane surface from 35 degrees to more than 40 degrees due to Hb binding, but no change of the predominantly alpha-helical secondary structures of Hb due to LPS binding. From isothermal titration calorimetry, the molar [Hb] : [endotoxin] binding ratio lies between 1 : 3 and 1 : 5 molar. Synchrotron radiation X-ray diffraction measurements indicate a reorientation of the lipid A aggregates from one cubic structure to another, the final structure belonging to space group Q224. The LPS-induced TNF-alpha production of mononuclear cells is enhanced by Hb, whereas in the LAL assay an LPS concentration-dependent increase or decrease was observed. Although a detailed mechanism of action cannot be given, the enhancement of LPS bioactivity can be understood in the light of the previously presented conformational concept; Hb induces an increase in the conical shape of the lipid A moiety of LPS, higher cross-section of the hydrophobic than the hydrophilic part, and of the inclination angle of the diglucosamine backbone with respect to the direction of the acyl chains.

Properties of an extracellular polysaccharide produced by a strain of enterobacter isolated from pond water

A bacterium which was isolated from pond water and identified as Enterobacter cloacae produced a viscous extracellular polysaccharide when it was grown aerobically in a medium containing sucrose as a sole source of carbon. The maximum molecular weight of the polysaccharide was about 9.0 x 10(5). The polysaccharide was composed of fucose, galactose, glucose, and glucuronic acid in a molar ratio of 2:3:2:1, but the molecular weight and the molar ratio of the sugar component were different from those of the polysaccharide produced by the same species reported elsewhere.

In vivo modification of porin activity conferring antibiotic resistance to Enterobacter aerogenes

Cephalosporins are widely used in chemotherapy of bacterial infections and resistance mechanisms seriously impair their antibacterial activity. Several resistant strains of Enterobacter aerogenes, a frequently isolated nosocomial pathogen, were analyzed. One isolate exhibited a strong modification of the porin antigenic pattern, especially with an immunological probe directed against an epitope located inside the pore lumen. A strong decrease of cefepime uptake was evidenced for this isolate, similarly to ones observed for porin-deficient strains: these kinetics show a serious alteration of the channel properties which may support cephalosporin resistance. This is the first E. aerogenes isolate using such adaptive response which defines an original enterobacterial answer to cephalosporin.

A simple method for the isolation and purification of L-asparaginase from Enterobacter aerogenes

L-Asparaginase from Enterobacter aerogenes was purified by a simple method involving sonication of the crude cell mass, gel filtration with Sephacryl S-100 as the separating material, followed by ultrafiltration. Recent methods involve complex purification procedures of 5-6 steps. The isolation process resulted in 10-fold purification of the enzyme with a specific activity of 55 IU/mg protein and recovery of 54%. The purity was tested by capillary electrophoresis, used for the first time for documenting the purification of L-asparaginase. The choice of the column material was critical in the purification process.

Alanine dehydrogenase from Enterobacter aerogenes: purification, characterization, and primary structure

Alanine dehydrogenase [EC 1. 4. 1. 1] was purified to homogeneity from a crude extract of Enterobacter aerogenes ICR 0220. The enzyme had a molecular mass of about 245 kDa and consisted of six identical subunits. The enzyme showed maximal activity at about pH 10.9 for the deamination of L-alanine and at about pH 8.7 for the amination of pyruvate. The enzyme required NAD+ as a coenzyme. Analogs of NAD+, deamino-NAD+ and nicotinamide guanine dinucleotide served as coenzymes. Initial-velocity and product inhibition studies suggested that the deamination of L-alanine proceeded through a sequential ordered binary-ternary mechanism. NAD+ bound first to the enzyme, followed by L-alanine, and the products were released in the order of ammonia, pyruvate, and NADH. The Km were 0.47 mM for L-alanine, 0.16 mM for NAD+, 0.22 mM for pyruvate, 0.067 mM for NADH, and 66.7 mM for ammonia. The Km for L-alanine was the smallest in the alanine dehydrogenases studied so far. The enzyme gene was cloned into Escherichia coli JM109 cells and the nucleotides were sequenced. The deduced amino acid sequence was very similar to that of the alanine dehydrogenase from Bacillus subtilis. However, the Enterobacter enzyme has no cysteine residue. In this respect, the Enterobacter enzyme is different from other alanine dehydrogenases.

Acid and base hydrolysis of lipid A from Enterobacter agglomerans as monitored by electrospray ionization mass spectrometry: pertinence to detoxification mechanisms

Lipopolysaccharides (LPS), which are endotoxins found in the cell wall of Gram-negative bacteria, are common components of organic dusts that cause or contribute to symptoms associated with organic dust diseases. The lipid A subgroup within LPS is believed to be responsible for the toxicity. Acid and base treatments, which can be effective detoxification methods, were performed on lipid A from Enterobacter agglomerans (EA), a bacterium commonly found in field cotton. Negative-ion electrospray ionization mass spectrometry was employed to characterize the post-treatment structural changes to lipid A. Acid treatment (1% acetic acid, 100 degrees C) hydrolyzed the ester side-chains of lipid A. It was found that the ester-linked palmitoyl group was the most labile to acid hydrolysis. Hydrolysis of the palmitoyl moiety conformed to pseudo-first-order chemical reaction kinetics with a rate constant for decomposition of heptacyl-lipid A from Enterobacter agglomerans of approximately 3.3 x 10(-3) min-1. An order of lability of lipid A acyl side-chains to acid hydrolysis was also deduced: R4' (palmitoyl) > R1' (myristoyl or hydroxymyristoyl) > R3 (hydroxymyristoyl at position 3) > R1 (oxymyristoyl group at position 3') > R2' (lauroyl). Base treatment (0.05 M NaOH in 95% EtOH, 65 degrees C) was shown to be more effective at cleaving ester-linked side-chains. In addition, mass spectral evidence suggests that opening of the pyranose rings of the disaccharide backbone of lipid A and/or removal of the phosphoryl groups may be occurring during base treatment. This study sheds light on mechanistic aspects of treatment procedures leading to the detoxification of endotoxins.

[Resistance to imipenem in Enterobacter aerogenes]

BACKGROUND

In June, 1993, an Enterobacter aerogenes strain was isolated in the Hospital de la Creu Roja from Hospitalet de Llobregat (Barcelona), which was resistant against all beta-lactams, including imipenem. Since is unusual in Enterobacter sp. to isolate imipenem resistant strains, we decided to study its resistance mechanism.

METHODS

To study the E. aerogenes 174004/H resistance mechanism beta-lactamase isoelectrofocalization was performed together with the determination of kinetic constants in order to characterize the beta-lactamase, and a polyacrylamide gel electrophoresis in order to observe the profile.

RESULTS

The strain of E. aerogenes 174004/H exhibits a chromosomic beta-lactamase with a pI higher than 9.2 and a decrease in an outer membrane protein of 42 kDa, probably a porine.

CONCLUSIONS

E. aerogenes 174004/H resistance against imipenem is due to an hyperproduction of a chromosomic beta-lactamase with a pI higher than 9.2 and to a 42 kDa decrease of an outer membrane protein expression.

Cloning and nucleotide sequence of the signal peptidase II (lsp)-gene from Staphylococcus carnosus

Staphylococcus carnosus TM300 is able to synthesize at least seven lipoproteins with molecular masses between 15 and 45 kDa; the proteins are located in the membrane fraction. It can be concluded that this strain also posesses the enzymes involved in lipoprotein modification and prolipoprotein signal peptidase (signal peptidase II) processing. The gene encoding the prolipoprotein signal peptidase, lsp, from Staphylococcus carnosus TM300 was cloned in Escherichia coli and sequenced. The deduced amino acid sequence of the Lsp showed amino acid similarities with the Lsp's of S. aureus, Enterobacter aerogenes, E. coli, and Pseudomonas fluorescens. The hydropathy profile reveals four hydrophobic segments which are homologous to the putative transmembrane regions of the E. coli signal peptidase II. E. coli strains carrying lsp of S. carnosus exhibited an increased globomycin resistance.

Capillary zone electrophoresis assay of the uridine diphosphate N-acetylmuramyl peptide precursors and the disaccharide pentapeptide derivative of bacterial cell wall peptidoglycan

Uridine diphosphate N-acetylmuramyl peptide (EDP-MurNac) precursors and disaccharide pentapeptide of bacterial cell wall peptidoglycan were extracted from Enterobacter colacae cells and examined by capillary zone electrophoresis. Five UDP-MurNac derivatives with dibromopropamidine isethionate as the internal standard, and disaccharide pentapeptide with pyrimethamine as the internal standard, were successfully and rapidly analysed by using a fused-silica capillary and sodium phosphate buffer in methanol as the organic modifier at appropriate pH. Accurate quantitation was also achieved. The method provides the potential to investigate quantitatively the effect of antibacterials on the biosynthesis of peptidoglycan and to determine the relative cellular concentrations of the murein precursors within the cell cycle.

Electrospray mass spectrometry for characterization of lipid A from Enterobacter agglomerans

Negative ion and positive ion electrospray mass spectrometry have been employed to characterize the lipid A mixture produced by hydrolysis of lipopolysaccharides from Enterobacter agglomerans, a Gram-negative bacterium commonly found in field cotton. Neutral monophosphoryl lipid A molecules form stable anions via deprotonation, but adduct formation via cation attachment occurs in low yield. Dephosphorylated lipid A molecules, on the other hand, readily form adducts with Na+, whereas deprotonation occurs in low yield. The mass spectra of lipid A produced by E. agglomerans reveal the presence of lipid A ions which differ in the nature of attached fatty acid side chains. At least two heptaacyl forms of lipid A are present, one of which has a structure which appears to be the same as the structure of heptaacyl lipid A produced by Salmonella minnesota. The second structure differs only by the nature of the side chain at position 3' of the disaccharide backbone where a hydroxymyristoyloxymyristoyl group replaces the myristoyloxymyristoyl substituent. Collisionally activated dissociations prior to mass analysis enable the identification of fragment ions which can be distinguished from at least eight intact deprotonated molecules present in crude lipid A.