More recently, the biological colonization of stone heritage and consequently its biodeterioration has become the focus of numerous studies. Among all microorganisms, fungi are considered to be one of the most important colonizers and biodegraders on stone materials. This is why the development of new antifungal materials requires immediate action. ZnMgO nanoparticles (NPs) have several exciting applications in different areas, highlighting as an efficient antimicrobial agent for medical application. In this research, the application of Zn-doped MgO (Mg1–x Zn x O, x = 0.096) NPs obtained by sol–gel method as antifungal coatings on dolomitic and calcitic stones has been explored as a means to develop effective protective coatings for stone heritage. Moreover, the photocatalytic and antifungal activity of Mg1–x Zn x O NPs were comparatively studied with single ZnO and MgO NPs. Thus, compared to the MgO and ZnO nanomaterials, the Mg1–x Zn x O NPs exhibited an enhanced photocatalytic activity. After UV irradiation for 60 min, 87% methylene blue was degraded over Zn-doped MgO NPs, whereas only 58% and 38% of MB was degraded over ZnO and MgO NPs, respectively. These nanoparticles also displayed a better antifungal activity than that of single pure MgO or ZnO NPs, inhibiting the growth of fungi Aspergillus niger, Penicillium oxalicum, Paraconiothyrium sp., and Pestalotiopsis maculans, which are especially active in the bioweathering of stone. The improved photocatalytic and antifungal properties detected in the Mg1–x Zn x O NPs was attributed to the formation of crystal defects by the incorporation of Zn into MgO. The application of the MgO- and Zn-doped MgO NPs as protective coatings on calcareous stones showed important antifungal properties, inhibiting successfully the epilithic and endolithic colonization of A. niger and P. oxalicum in both lithotypes, and indicating a greater antifungal effectiveness on Zn-doped MgO NPs. The use of Zn-doped MgO NPs may thus represent a highly efficient antifungal protection for calcareous stone heritage.

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The presence and deteriorating action of microbial biofilms on historic stone buildings have received considerable attention in the past few years. Among microorganisms, fungi are one of the most damaging groups. In the present work, antimicrobial surfaces were prepared using suspensions of Ca(OH)2 particles, mixed with ZnO or TiO2 nanoparticles. The antimicrobial surfaces were evaluated for their antifungal activity both in the dark and under simulated natural photoperiod cycles, using Penicillium oxalicum and Aspergillus niger as model organisms, and two limestone lithotypes commonly used in construction and as materials for the restoration of historic buildings. Both Ca(OH)2-ZnO and Ca(OH)2-TiO2 materials displayed antifungal activity: ZnO-based systems had the best antifungal properties, being effective both in the dark and under illumination. In contrast, TiO2-based coatings showed antifungal activity only under photoperiod conditions. Controls with coatings consisting of only Ca(OH)2 were readily colonized by both fungi. The antifungal activity was monitored by direct observation with microscope, X-ray diffraction (XRD), and scanning electron microscopy (SEM), and was found to be different for the two lithotypes, suggesting that the mineral grain distribution and porosity played a role in the activity. XRD was used to investigate the formation of biominerals as indicator of the fungal attack of the limestone materials, while SEM illustrated the influence of porosity of both the limestone material and the coatings on the fungal penetration into the limestone. The coated nanosystems based on Ca(OH)2-50%ZnO and pure zincite nanoparticulate films have promising performance on low porosity limestone, showing good antifungal properties against P. oxalicum and A. niger under simulated photoperiod conditions.

A previously reported bacterial bioemulsifier, here termed microbactan, was further analyzed to characterize its lipid component, molecular weight, ionic character and toxicity, along with its bioemulsifying potential for hydrophobic substrates at a range of temperatures, salinities and pH values. Analyses showed that microbactan is a high molecular weight (700 kDa), non-ionic molecule. Gas chromatography of the lipid fraction revealed the presence of palmitic, stearic, and oleic acids; thus microbactan may be considered a glycolipoprotein. Microbactan emulsified aromatic hydrocarbons and oils to various extents; the highest emulsification index was recorded against motor oil (96%). The stability of the microbactan-motor oil emulsion model reached its highest level (94%) at 50 °C, pH 10 and 3.5% NaCl content. It was not toxic to Artemia salina nauplii. OPEN ACCESS Int. J. Mol. Sci. 2013, 14 18960Microbactan is, therefore, a non-toxic and non-ionic bioemulsifier of high molecular weight with affinity for a range of oily substrates. Comparative phylogenetic assessment of the 16S rDNA gene of Microbacterium sp. MC3B-10 with genes derived from other marine Microbacterium species suggested that this genus is well represented in coastal zones. The chemical nature and stability of the bioemulsifier suggest its potential application in bioremediation of marine environments and in cosmetics.

Avocado (Persea americana) and papaya (Carica papaya) are tropical fruits with high international demand. However, these commercially important crops are affected by the fungus Colletotrichum gloeosporioides, which causes anthracnose and results in significant economic losses. The antifungal activity of metal oxide nanomaterials (zinc oxide (ZnO), magnesium oxide (MgO), and ZnO:MgO and ZnO:Mg(OH)2 composites) prepared under different conditions of synthesis was evaluated against strains of C. gloeosporioides obtained from papaya and avocado. All nanoparticles (NPs) at the tested concentrations significantly inhibited the germination of conidia and caused structural damage to the fungal cells. According to the radial growth test, the fungal strain obtained from avocado was more susceptible to the NPs than the strain obtained from papaya. The effect of the tested NPs on the fungal strains confirmed that these NPs could be used as strong antifungal agents against C. gloeosporioides to control anthracnose in tropical fruits.

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Aims:  Isolation and antimicrobial evaluation of aquatic bacterial strains from two cenotes. Methods and Results:  A total of 258 bacterial strains were isolated from the water and sediment of two cenotes in the Yucatan peninsula, all of which were screened against six pathogenic micro‐organisms. Antimicrobial activity was detected in 46 of the isolated strains against at least one of the target strains tested. Antimicrobially active isolates were identified as: Aeromonas, Bacillus, Burkholderia, Photobacterium, Pseudomonas, Serratia, Shewanella, Stenotrophomonas genera, and 13 remained unidentified. All antimicrobially active strains were able to grow in salt medium at a concentration of 75 g l−1, thus classifying as moderately halotolerant bacteria. Most of the antimicrobially active strains exhibited a broad action spectrum, where 61% was because of uncharacterized antimicrobial substances, 25% because of bacteriocins and 13% because of siderophores. Ten strains were able to biosynthesize biosurfactant metabolites. Conclusions:  Native bacteria from the Yucatan peninsula showed an interesting antimicrobial activity, diverse mode of action and moderate halotolerance to salt. Significance and Impact of the Study:  This is the first report on bacterial isolates from cenotes of the Yucatan peninsula and their antimicrobial characterization, with great potential for future biotechnological applications.