Characterization of Distinct Biofilm Cell Subpopulations and Implications in Quorum Sensing and Antibiotic Resistance

Bacteria change phenotypically in response to their environment. Free swimming cells transition to biofilm communities that promote cellular cooperativity and resistance to stressors and antibiotics. We uncovered three subpopulations of cells with diverse phenotypes from a single-species Pseudomonas aeruginosa PA14 biofilm, and used a series of steps to isolate, characterize, and map these cell subpopulations in a biofilm. The subpopulations were distinguishable by size and morphology using dynamic light scattering (DLS) and scanning electron microscopy (SEM). Additionally, growth and dispersal of biofilms originating from each cell subpopulation exhibited contrasting responses to antibiotic challenge. Cell subpopulation surface charges were distinctly different, which led us to examine the ionizable surface molecules associated with each subpopulation using mass spectrometry. Matrix assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry analysis of cell subpopulations revealed ions unique to each subpopulation of cells that significantly co-localized with ions associated with quorum sensing. Transcript levels of algR, lasR, and rhlI in subpopulations isolated from biofilms differed from levels in planktonic stationary and mid-log cell subpopulations. These studies provide insight into diverse phenotypes, morphologies, and biochemistries of PA14 cell subpopulations for potential applications in combating bacterial pathogenesis, with medical, industrial, and environmental complications.

One-step synthesis of blue-green luminescent carbon dots by a low-temperature rapid method and their high-performance antibacterial effect and bacterial imaging

Due to the global infection problem caused by the abuse of antibiotics, the preparation of novel antibacterial nanomaterials is a key and basic requirement for applications in antibacterial and bacterial imaging fields. This paper reports the one-step preparation of blue-green-emitting carbon dots (CDs) under low temperature (80 °C) with glucose as the carbon source, citric acid as the dehydrating agent, and polyethyleneimine as the nitrogen source. Through inhibition zone tests and minimum inhibitory concentration (MIC) experiments, the inhibitory abilities of prepared CDs against various microorganisms, including gram-positive bacteria, gram-negative bacteria and fungi, were compared. It is worth mentioning that the MIC of CDs against Staphylococcus aureus reaches 4.7 μg ml^-1, and the CDs exhibit excellent biocompatibility. Moreover, studies on visual-treatment therapy, in which infection treatment can be performed at the same time as bacterial imaging, with the prepared functional antibacterial CDs based on fluorescence confocal imaging would be beneficial to their promising future in medical and biological fields.

Thermodynamic characterization of proton-ionizable functional groups on the cell surfaces of ammonia-oxidizing bacteria and archaea

The ammonia-oxidizing archaeon Nitrosopumilus maritimus strain SCM1 (strain SCM1), a representative of the Thaumarchaeota archaeal phylum, can sustain high specific rates of ammonia oxidation at ammonia concentrations too low to sustain metabolism by ammonia-oxidizing bacteria (AOB). One structural and biochemical difference between N. maritimus and AOB that might be related to the oligotrophic adaptation of strain SCM1 is the cell surface. A proteinaceous surface layer (S-layer) comprises the outermost boundary of the strain SCM1 cell envelope, as opposed to the lipopolysaccharide coat of Gram-negative AOB. In this work, we compared the surface reactivities of two archaea having an S-layer (strain SCM1 and Sulfolobus acidocaldarius) with those of four representative AOB (Nitrosospira briensis, Nitrosomonas europaea, Nitrosolobus multiformis, and Nitrosococcus oceani) using potentiometric and calorimetric titrations to evaluate differences in proton-ionizable surface sites. Strain SCM1 and S. acidocaldarius have a wider range of proton buffering (approximately pH 10-3.5) than the AOB (approximately pH 10-4), under the conditions investigated. Thermodynamic parameters describing proton-ionizable sites (acidity constants, enthalpies, and entropies of protonation) are consistent with these archaea having proton-ionizable amino acid side chains containing carboxyl, imidazole, thiol, hydroxyl, and amine functional groups. Phosphorous-bearing acidic functional groups, which might also be present, could be masked by imidazole and thiol functional groups. Parameters for the AOB are consistent with surface structures containing anionic oxygen ligands (carboxyl- and phosphorous-bearing acidic functional groups), thiols, and amines. In addition, our results showed that strain SCM1 has more reactive surface sites than the AOB and a high concentration of sites consistent with aspartic and/or glutamic acid. Because these alternative boundary layers mediate interaction with the local external environment, these data provide the basis for further comparisons of the thermodynamic behavior of surface reactivity toward essential nutrients.

Lack of influence of extracellular polymeric substances (EPS) level on hydroxyl radical mediated disinfection of Escherichia coli

Photolysis of nitrate, a prevalent constituent in agriculturally impacted waters, may influence pathogen attenuation in such systems through production of hydroxyl radical ((•)OH). This study focuses on the efficacy of (•)OH generated during nitrate photolysis in promoting E. coli die-off as a function of extracellular polymeric substances (EPS) coverage. EPS levels of four E. coli isolates were systematically altered through a sonication extraction method and photochemical batch experiments with a solar simulator examined isolate viability loss as a function of time in nitrate solutions. E. coli viability loss over time exhibited two regimes: an initial induction time, t(s), with little decay was followed by rapid exponential decay characterized by a first-order disinfection rate constant, k. Increasing steady-state (•)OH concentrations enhanced E. coli viability loss, increasing values of k and decreasing t(s) values, both of which were quantified with a multitarget bacterial disinfection model. Notably, at a given steady-state (•)OH concentration, values of t(s) and k were independent of EPS levels, nor did they vary among the different E. coli strains considered. Results herein show that while (•)OH generated via nitrate photolysis enhances rates of disinfection in surface water, the mechanism by which (•)OH kills E. coli is relatively insensitive to common bacterial variables.

Spectroscopic Study of Extracellular Polymeric Substances fromBacillussubtilis: Aqueous Chemistry and Adsorption Effects

Reactions at ionizable functional groups in extracellular polymeric substances (EPS) from Bacillus subtilis are found to affect aqueous phase conformation and adsorption to mineral surfaces. Characterization by HPSEC, XPS, and FTIR indicates a wide range in apparent molecular mass (0.57-128 kDa), with functional group composition depending on cell growth phase (exponential vs stationary) and location in suspension (free vs cell-bound). ATR-FTIR spectroscopy shows complexation and dissociation of protons on acidic functional groups that result in alpha-helical protein conformation at pH < 2.6 and random coil (unordered) conformation at higher pH (>6). EPS exhibit higher affinity for adsorption to alpha-FeOOH than amorphous SiO(2) because of surface charge effects. Increased amide II band intensity and an amide I band shift to higher frequency indicate changes in protein structure upon adsorption. Goethite-EPS spectra show emergent vibrations consistent with P-O-Fe bonding, which suggests a role of phosphodiester groups in the adsorption reaction.

Differentiation of capsular polysaccharides from Acetobacter diazotrophicus strains isolated from sugarcane

Capsular polysaccharides (CPSs) from six representative strains of Acetobacter diazotrophicus were isolated and fractionated by gel filtration and anion-exchange chromatography. Purified CPSs obtained in the non-adsorbed fraction of a DEAE-Sephadex A-25 column were qualitatively and quantitatively analyzed for sugar composition. Uronic acid and amino sugars were not detected in all purified CPSs. Basically the CPSs of A. diazotrophicus are composed of rhamnose, mannose, galactose and glucose. The presence of fucose was only observed in the CPS of strains PR2 and PAL3. Based on these results, the six strains of A. diazotrophicus could be divided into four groups according to the sugar content of their capsules: (i) fucose-containing capsules (PR2 and PAL3, localized in roots), (ii) mannose-rich capsule (PAL5, localized in root), (iii) capsules with a high ratio of hexose to rhamnose (PR4 and PR20, localized in stems) and (iv) capsules with a low ratio of hexose to rhamnose (PR14, localized in rhizosphere). For all CPSs, sodium dodecy sulfate-polyacrylamide gel electrophoresis showed diffuse bands of slow mobility in silver-stained gels. The different CPS migration patterns could not be correlated with sugar composition. The purified CPS of strain PAL3 was found to be immunogenic and immunochemically similar to the CPS of strain PR2. The serological specificity to CPS of strains PAL3 and PR2 correlated well with the presence of focuse, indicating that this deoxyhexose is immunodominant.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and characterization of a generalized transducing phage for Xanthomonas campestris pv. campestris

We have isolated and characterized a lytic double-stranded DNA Xanthomonas campestris pv. campestris bacteriophage (XTP1) capable of mediating generalized transduction. The phage transduces chromosomal markers at frequencies of 10(-5) to 10(-6) transductants per PFU. We demonstrated its genetic utility by the isolation and cotransduction of linked transposon insertions to a nonselectable locus, xgl, required for the cleavage of 5-bromo-3-chloro-indoyl-beta-D-galactoside and showed that rif and str alleles in X. campestris are 75% linked. One-step growth experiments showed that the latent and rise periods were each 2 h and the average burst size was 35. The DNA genome is approximately 180 kb, presumably modified in a sequence-specific manner, and may be covalently attached to protein(s). Electron micrographs show the phage particle to have an icosahedral head and contractile tail with tail fibers uniquely attached to a location 40 nm proximal from the end of the tail.

Mineral Precipitation by Epilithic Biofilms in the Speed River, Ontario, Canada

Epilithic microbial communities, ubiquitously found in biofilms on submerged granite, limestone, and sandstone, as well as on the concrete support pillars of bridges, were examined in the Speed River, Ontario, Canada. Transmission electron microscopy showed that attached bacteria (on all substrata) were highly mineralized, ranging from Fe-rich capsular material to fine-grained (<1 μm) authigenic (primary) mineral precipitates. The authigenic grains exhibited a wide range of morphologies, from amorphous gel-like phases to crystalline structures. Energy-dispersive X-ray spectroscopy indicated that the most abundant mineral associated with epilithic bacteria was a complex (Fe, Al) silicate of variable composition. The gel-like phases were similar in composition to a chamositic clay, whereas the crystalline structures were more siliceous and had compositions between those of glauconite and kaolinite. The consistent formation of (Fe, Al) silicates by all bacterial populations, regardless of substratum lithology, implies that biomineralization was a surface process associated with the anionic nature of the cell wall. The adsorption of dissolved constituents from the aqueous environment contributed significantly to the mineral formation process. In this regard, it appears that epilithic microbial biofilms dominate the reactivity of the rock-water interface and may determine the type of minerals formed, which will ultimately become part of the riverbed sediment. Because rivers typically contain high concentrations of dissolved iron, silicon, and aluminum, these findings provide a unique insight into biogeochemical activities that are potentially widespread in natural waters.

Control of extracellular polysaccharide synthesis in Erwinia stewartii and Escherichia coli K-12: a common regulatory function

A primary determinant of pathogenicity in Erwinia stewartii is the production of extracellular polysaccharide (EPS). A single mutation can abolish both EPS synthesis and pathogenicity; both properties are restored by a single cosmid clone. Subcloning and insertion analysis have defined a single positive regulatory function which shares a number of similarities with the rcsA function of Escherichia coli K-12, a positive regulator for capsular polysaccharide synthesis. In E. stewartii, the gene promotes the transcription of at least two operons (cps) involved in EPS synthesis; we have previously demonstrated a similar function for rcsA in E. coli. Both genes code for proteins of 25 to 27 kilodaltons; both proteins are unstable in E. coli. The E. stewartii RcsA protein was stabilized in E. coli lon mutants, as the RcsA product from E. coli is. The E. stewartii function complemented E. coli rcsA mutants, and the E. coli RcsA function increased cps expression and restored virulence in E. stewartii mutants. Therefore, these two gram-negative organisms share a similar component of their regulatory circuitry for the control of capsular polysaccharide synthesis.