Characterization of extracellular polymeric substances in the biofilms of typical bacteria by the sulfur K-edge XANES spectroscopy

The activity of hydrolytic enzymes and antibiotics against biofilms of bacteria isolated from industrial-scale cooling towers

BACKGROUND

Cooling towers (CTs) are crucial to myriad industrial processes, supporting thermal exchange between fluids in heat exchangers using water from lakes and rivers as coolant. However, CT water can sometimes introduce microbial contaminants that adhere to and colonize various surfaces within the CT system. These microorganisms can form biofilms, significantly hindering the system's thermal exchange efficiency. Current treatment strategies employ oxidizing biocides to prevent microbial growth. However, despite their affordability, they do not eliminate biofilms effectively and can lead to corrosive damage within the system. Herein, we aim to devise an anti-biofilm strategy utilizing hydrolytic enzymes (such as α-amylase, glucoamylase, pectin-lyase, cellulase, protease, and DNase) alongside antibiotics (including meropenem, ciprofloxacin, gentamicin, erythromycin, chloramphenicol, and ceftriaxone) to combat microbial growth and biofilm formation in cooling systems.

RESULTS

All enzymes reduced the development of the biofilms significantly compared to controls (p < 0.05). The polysaccharidases exhibited biomass reduction of 90%, except for pectin-lyase (80%), followed by DNAse and protease at 43% and 49%, respectively. The antibiotics reduced the biofilms of 70% of isolates in concentration of > 2 mg/mL. The minimal biofilm eradication concentration (MBEC) lower than 1 mg/mL was detected for some 7-day-old sessile isolates. The enzymes and antibiotics were also used in combination against biofilms using the modified Chequerboard method. We found six synergistic combinations, with Fractional inhibitory concentrations (FIC) < 0.5, out of the ten tested. In the presence of the enzymatic mixture, MBECs presented a significant decrease (p < 0.05), at least 4-fold for antibiotics and 32-fold for enzymes. Moreover, we characterized high molecular weight (> 12 kDa) exopolysaccharides (EPS) from biofilms of ten isolates, and glycosyl composition analysis indicated a high frequency of glucose, mannose, erythrose, arabinose, and idose across isolates EPS contrasting with rhamnose, allose, and those carbohydrates, which were detected in only one isolate.

CONCLUSION

The synergistic approach of combining enzymes with antibiotics emerges as a highly effective and innovative strategy for anti-biofilm intervention, highlighting its potential to enhance biofilm management practices.

Functional group diversity for the adsorption of lead(Pb) to bacterial cells and extracellular polymeric substances

Bacteria and their secreted extracellular polymeric substances (EPS) are widely distributed in ecosystems and have high capacity for heavy metal immobilization. The knowledge about the molecular-level interactions with heavy metal ions is essential for predicting the behavior of heavy metals in natural and engineering systems. This comprehensive study using potentiometric titration, Fourier-transform infrared (FTIR) spectroscopy, isothermal titration calorimetry (ITC) and X-ray absorption fine structure (XAFS) was able to reveal the functional diversity and adsorption mechanisms for Pb onto bacteira and the EPS in greater detail than ever before. We identified mono-carboxylic, multi-carboxylic, phosphodiester, phosphonic and sulfhydryl sites and found the partitioning of Pb to these functional groups varied between gram-negative and gram-positive bacterial strains, the soluble and cell-bound EPS and Pb concentrations. The sulfhydryl and phosphodiester groups preferentially complexed with Pb in P. putida cells, while multifunctional carboxylic groups promoted Pb adsorption in B. subtilis cells and the protein fractions in EPS. Though the functional site diversity, the adsorption of Pb to organic ligands occurred spontaneously through a universal entropy increase and inner-sphere complexation mechanism. The functional group scale knowledge have implications for the modeling of heavy metal behavior in the environment and application of these biological resources.

Organic composition of epilithic biofilms from agricultural and urban watershed in South Brazil

Active functional groups in biofilms determine the adsorption and desorption of contaminants and nutrients. Epilithic biofilms were characterized in order to understand the association between the chemistry alteration patterns and the surrounding anthropic activities of the Guaporé River watershed. The instrumental analyses included pyrolysis coupled to gas chromatography and mass spectroscopy, spectroscopy in the IR region with attenuated total reflectance, and two-dimensional nuclear magnetic resonance. Spectrometric techniques demonstrated that epilithic biofilms are mainly composed of polysaccharides, nitrogen-containing compounds, lipids, and aromatic and phenolic structures, which have functional groups characteristic of alcohols, esters, ethers, and amides. The polysaccharide levels reflect well the environmental pressures. The chemical composition of epilithic biofilms can be an effective tool for environmental assessment in watercourses, since the different anthropic actions developed in watersheds, mainly agriculture and urban areas, can modify the organic fraction of biofilms.

Elucidation of crude siderophore extracts from supernatants of Pseudomonas sp. ZnCd2003 cultivated in nutrient broth supplemented with Zn, Cd, and Zn plus Cd

This research aimed to study siderophores secreted from Pseudomonas sp. PDMZnCd2003, a Zn/Cd tolerant bacterium. The effects of Zn and/or Cd stress were examined in nutrient broth to achieve the actual environmental conditions. Acid and alkali supernatants and liquid-liquid extraction with ethyl acetate and butanol were carried out to obtain crude extracts containing different amounts of the metals. The bacterial growth, UV-visible spectra of the supernatants and siderophore production indicated that the production of siderophores tended to be linked to primary metabolites. Pyocyanin was produced in all treatments, while pyoverdine was induced by stress from the metals, especially Cd. FT-IR spectra showed C=O groups and sulfur functional groups that were involved in binding with the metals. LC-MS revealed that pyocyanin, 1-hydroxy phenazine, pyoverdine, and pyochelin were present in the crude extracts. S K-edge XANES spectra showed that the main sulfur species in the extracts were the reduced forms of sulfide, thiol, and disulfide, and their oxidation states were affected by coordination with Zn and/or Cd. In addition, Zn K-edge EXAFS spectra and Cd K-edge EXAFS spectra presented Zn-O and Cd-O as coordination in the first shell, in case the extracts contained less metal. Although the mix O/S ligands had chelation bonding with Zn and Cd in the other extracts. For the role of S groups in pyochelin binding with the metals, this was the first report. The results of these experiments could be extended to Pseudomonas that respond to metal contaminated environments.

Thermochemistry of sulfur during pyrolysis and hydrothermal carbonization of sewage sludges

Sulfur (S) is an abundant and redox-active element in urban wastewater systems and plays a critical role in both the wastewater and sludge treatment processes. This study comparatively characterized the transformation of S and several closely associated metals (Cu, Zn, and Fe) during pyrolysis (250 to 750 °C) and hydrothermal carbonization (HTC, 150 to 275 °C) treatments of sewage sludge. S, Fe, Zn, and Cu K-edge X-ray absorption spectroscopy was applied to quantitatively evaluate the fate of S and contribution of different S species in regulating metal speciation. During pyrolysis, aliphatic-S and sulfonate were preferentially degraded at low temperature (below 350 °C) and sulfate was thermochemically reduced at temperature above 450 °C, while metal sulfides (up to 27%) and thiophenes (up to 70%) were increasingly formed. Similar to the pyrolysis process, metal sulfides (up to 40% at temperature above 200 °C) and thiophenes were formed during HTC. The degradation of thiols and organic sulfide, as well as sulfate reduction, released sulfide and strongly affected metal speciation. For example, almost all Cu and half of Zn were transformed into Cu-Fe- or Zn-Fe-sulfides during HTC, whereas they were partially desulfidized during pyrolysis. High abundance of reduced S species (S^-1 and S^-2) in hydrochars may contribute to their strong reductive adsorption of Cr(VI). Results from this work reveal the thermochemical reactions driving the transformations of S and its associated metals during pyrolysis and HTC. The results provide fundamental knowledge for selecting thermochemical sludge treatment techniques for value-added applications of the products.

Role of bacterial cell surface sulfhydryl sites in cadmium detoxification by Pseudomonas putida

Understanding bacterial metal detoxification systems is crucial for determining the environmental impacts of metal pollution and for developing advanced bioremediation and water disinfection strategies. Here, we explore the role of cell surface sulfhydryl sites in bacterial detoxification of Cd, using Pseudomonas putida with surface sulfhydryl sites mostly on its EPS molecules as a model organism. Our results show that 5 and 20 ppm Cd in LB growth medium affects the lag phase of P. putida, but not the overall extent of cell growth at stationary phase, indicating that P. putida can detoxify Cd at these concentrations. EXAFS analysis of Cd bound to biomass from the different growth stages indicates that Cd binds to both sulfhydryl and non-sulfhydryl sites, but that the importance of Cd-sulfhydryl binding increases from early exponential to stationary phase. Cell growth is positively correlated to the measured sulfhydryl concentration on different biomass samples, but is independent of the measured non-sulfhydryl binding site concentration on the cell surfaces. Taken together, our results demonstrate that the sulfhydryl binding sites on EPS molecules can play an important role in binding and detoxifying toxic metals, significantly decreasing the bioavailability of the metal by sequestering it away from the bacterial cells.