Lichenysin-like Polypeptide Production by Bacillus licheniformis B3-15 and Its Antiadhesive and Antibiofilm Properties

We report the ability of the crude biosurfactant (BS B3-15), produced by the marine, thermotolerant Bacillus licheniformis B3-15, to hinder the adhesion and biofilm formation of Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 29213 to polystyrene and human cells. First, we attempted to increase the BS yield, optimizing the culture conditions, and evaluated the surface-active properties of cell-free supernatants. Under phosphate deprivation (0.06 mM) and 5% saccharose, the yield of BS (1.5 g/L) increased by 37%, which could be explained by the earlier (12 h) increase in lchAA expression compared to the non-optimized condition (48 h). Without exerting any anti-bacterial activity, BS (300 µg/mL) prevented the adhesion of P. aeruginosa and S. aureus to polystyrene (47% and 36%, respectively) and disrupted the preformed biofilms, being more efficient against S. aureus (47%) than P. aeruginosa (26%). When added to human cells, the BS reduced the adhesion of P. aeruginosa and S. aureus (10× and 100,000× CFU/mL, respectively) without altering the epithelial cells' viability. As it is not cytotoxic, BS B3-15 could be useful to prevent or remove bacterial biofilms in several medical and non-medical applications.

Anti-Bacterial Adhesion on Abiotic and Biotic Surfaces of the Exopolysaccharide from the Marine Bacillus licheniformis B3-15

The eradication of bacterial biofilm represents a crucial strategy to prevent a clinical problem associated with microbial persistent infection. In this study we evaluated the ability of the exopolysaccharide (EPS) B3-15, produced by the marine Bacillus licheniformis B3-15, to prevent the adhesion and biofilm formation of Pseudomonas aeruginosa ATCC 27853 and Staphylococcus aureus ATCC 29213 on polystyrene and polyvinyl chloride surfaces. The EPS was added at different times (0, 2, 4 and 8 h), corresponding to the initial, reversible and irreversible attachment, and after the biofilm development (24 or 48 h). The EPS (300 µg/mL) impaired the initial phase, preventing bacterial adhesion even when added after 2 h of incubation, but had no effects on mature biofilms. Without exerting any antibiotic activity, the antibiofilm mechanisms of the EPS were related to the modification of the (i) abiotic surface properties, (ii) cell-surface charges and hydrophobicity, and iii) cell-to-cell aggregation. The addition of EPS downregulated the expression of genes (lecA and pslA of P. aeruginosa and clfA of S. aureus) involved in the bacterial adhesion. Moreover, the EPS reduced the adhesion of P. aeruginosa (five logs-scale) and S. aureus (one log) on human nasal epithelial cells. The EPS could represent a promising tool for the prevention of biofilm-related infections.

Hydrating Capabilities of the Biopolymers Produced by the Marine Thermophilic Bacillus horneckiae SBP3 as Evaluated by ATR-FTIR Spectroscopy

The surfactin-like lipopeptide (BS-SBP3) and the exopolysaccharide (EPS-SBP3) produced by the polyextremophilic Bacillus horneckiae SBP3 (DSM 103063) have been recently described as valuable biopolymers useful in biotechnological applications. To investigate the hydrating capabilities of BS-SBP3 and EPS-SBP3, here we evaluated (i) their wetting properties, measuring the contact angle; (ii) their moisture uptake abilities using the gravimetric method; and (iii) their hydrating states (from 0 to 160% w/w of water content) using ATR-FTIR spectroscopy. BS-SBP3 reduced the water contact angle on a hydrophobic surface from 81.7° to 51.3°, whereas the contact angle in the presence of EPS-SBP3 was 72.9°, indicating that BS-SBP3 improved the wettability of the hydrophobic surface. In the moisture uptake tests, EPS-SBP3 absorbed more water than BS-SBP3, increasing its weight from 10 mg to 30.1 mg after 36 h of 100% humidity exposure. Spectral distance and cross-correlation analyses were used to evaluate the molecular changes of the two biopolymers during the hydration process. As the water concentration increased, BS-SBP3 spectra changed in intensity in the two contributions of the OH-stretching band named "closed" and "open" (3247 and 3336 cm^-1, respectively). Differently, the spectra of EPS-SBP3 exhibited a broader peak (3257 cm^-1), which shifted at higher water concentrations. As evaluated by the spectral distance and the wavelet cross-correlation analysis, the OH-stretching bands of the BS-SBP3 and EPS-SBP3 changed as a function of water content, with two different sigmoidal trends having the inflection points at 80% and 48%, respectively, indicating peculiar water-properties of each biopolymer. As wetting agents, these biopolymers might replace industrially manufactured additives in agriculture and the food and cosmetic industries.

Nutritional conditions of the novel freshwater Coccomyxa AP01 for versatile fatty acids composition

AIMS

This study was to analyse the biomass production and fatty acids (FAs) profiles in a newly isolated chlorophyte, namely Coccomyxa AP01, under nutritionally balanced (NB) conditions (comparing nitrate and urea as nitrogen sources) and nitrogen or phosphate deprivation.

METHODS AND RESULTS

Lipid yields was about 30%-40% of dried biomasses in all examined nutritional conditions. Under NB conditions, lipids were principally constituted by monounsaturated FAs, mainly represented by oleic acid, and saturated and polyunsaturated FAs at similar concentrations. Nutrients deprivation induced remarkable changes in FAs profiles, with the highest amounts of saturated (42%-46%), followed by similar amounts of monounsaturated and polyunsaturated, and the emergence of rare long-chain FAs. Under phosphate deprivation, biomass yield was similar to NB conditions, with the highest yield of saturated (mainly palmitic acid) and of polyunsaturated FAs (33%) (mainly linoleic and linolenic acids).

CONCLUSIONS

Balanced or deprived nutritional conditions in Coccomyxa AP01 induced a selective production and composition of FAs. The phosphate-deprivation condition concomitantly provided high biomass yield and the production of high value saturated and polyunsaturated FAs with industrial interest.

SIGNIFICANCE AND IMPACT OF THE STUDY

Coccomyxa AP01 could be considered a promising source of different FAs, including also docosapentaenoic acid, for several commercial purposes spanning from biodiesel production, pharmaceutical and cosmetic applications to innovative aquaculture fish feeds.

Role of Phage Capsid in the Resistance to UV-C Radiations

The conformational variation of the viral capsid structure plays an essential role both for the environmental resistance and acid nuclear release during cellular infection. The aim of this study was to evaluate how capsid rearrangement in engineered phages of M13 protects viral DNA and peptide bonds from damage induced by UV-C radiation. From in silico 3D modelling analysis, two M13 engineered phage clones, namely P9b and 12III1, were chosen for (i) chemical features of amino acids sequences, (ii) rearrangements in the secondary structure of their pVIII proteins and (iii) in turn the interactions involved in phage capsid. Then, their resistance to UV-C radiation and hydrogen peroxide (H2O2) was compared to M13 wild-type vector (pC89) without peptide insert. Results showed that both the phage clones acquired an advantage against direct radiation damage, due to a reorganization of interactions in the capsid for an increase of H-bond and steric interactions. However, only P9b had an increase in resistance against H2O2. These results could help to understand the molecular mechanisms involved in the stability of new virus variants, also providing quick and necessary information to develop effective protocols in the virus inactivation for human activities, such as safety foods and animal-derived materials.

Marine Bacterial Exopolymers-Mediated Green Synthesis of Noble Metal Nanoparticles with Antimicrobial Properties

A straightforward and green method for the synthesis of gold, silver, and silver chloride nanoparticles (Au NPs and Ag/AgCl NPs) was developed using three different microbial exopolymers (EP) as reducing and stabilizing agents. The exopolysaccharides EPS B3-15 and EPS T14 and the poly-γ-glutamic acid γ-PGA-APA were produced by thermophilic bacteria isolated from shallow hydrothermal vents off the Eolian Islands (Italy) in the Mediterranean Sea. The production of metal NPs was monitored by UV-Vis measurements by the typical plasmon resonance absorption peak and their antimicrobial activity towards Gram-positive and Gram- negative bacteria (Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa), as well as fungi (Candida albicans) was investigated. The biological evaluation showed no activity for EP-Au NPs, except against E. coli, whereas EP-Ag NPs exhibited a broad-spectrum of activity. The chemical composition, morphology, and size of EP-Ag NPs were investigated by UV-Vis, zeta potential (ζ), dynamic light scattering (DLS) measurements and transmission electron microscopy (TEM). The best antimicrobial results were obtained for EPS B3-15-Ag NPs and EPS T14-Ag NPs (Minimum Inhibitory Concentration, MIC: 9.37-45 µg/mL; Minimum Bactericidal Concentration/Minimum Fungicidal Concentration, MBC/MFC: 11.25-75 µg/mL).

Comparing Spore Resistance of Bacillus Strains Isolated from Hydrothermal Vents and Spacecraft Assembly Facilities to Environmental Stressors and Decontamination Treatments

Submarine hydrothermal vents are inhabited by a variety of microorganisms capable of tolerating environmental extremes, making them ideal candidates to further expand our knowledge of the limitations for terrestrial life, including their ability to survive the exposure of spaceflight-relevant conditions. The spore resistance of two Bacillus spp. strains, APA and SBP3, isolated from two shallow vents off Panarea Island (Aeolian Islands, Italy), to artificial and environmental stressors (i.e., UVC radiation, X-rays, heat, space vacuum, hydrogen peroxide [H₂O₂], and low-pressure plasma), was compared with that of two close phylogenetic relatives (Bacillus horneckiae and Bacillus oceanisediminis). Additional comparisons were made with Bacillus sp. isolated from spacecraft assembly facilities (B. horneckiae, Bacillus pumilus SAFR-032, and Bacillus nealsonii) and the biodosimetry strain and space microbiology model organism Bacillus subtilis. Overall, a high degree of spore resistance to stressors was observed for the strains isolated from spacecraft assembly facilities, with an exceptional level of resistance seen by B. pumilus SAFR-032. The environmental isolate SBP3 showed a more robust spore resistance to UVC, X-rays, H₂O₂, dry heat, and space vacuum than the closely related B. horneckiae. Both strains (SBP3 and APA) were more thermotolerant than their relatives, B. horneckiae and B. oceanisediminis, respectively. SBP3 may have a novel use as a bacterial model organism for future interrogations into the potential of forward contamination in extraterrestrial environments (e.g., icy moons of Jupiter or Saturn), spacecraft sterilization and, broadly, microbial responses to spaceflight-relevant environmental stressors.