**5. Microbial degradation of wood**

The degradation of wood materials depends on physico-chemical and biological factors such as temperature, humidity, nutrients, and the type of wood (hardwood or softwood), specific to the environment in which they are exposed. Among the biological factors, insects, macro- and micromycetes, and bacteria, the microbial load of the environment, corroborated with humidity and temperature, plays an important role in the biodegradation processes of this material. Of the microbiological agents, the most common types of biodegradation are those caused by fungi and bacteria, which manage to degrade the wood through enzymatic mechanisms with the enzymes they are secreting. The fungi types that attack wood materials are divided into three classes:

isolated from funerary masks of degraded wood from Saqqara showed that the most effective of the tested materials is AgNPs, followed by CuNPs and TiNPs [79], both for fungi and bacteria (**Figures 8** and **9**). The action mechanism of AgNP includes processes such as adherence to microbial cells, penetration into cells, free radical generation, DNA and RNA damage [79, 80]. Another study performed on China's degraded wood objects [81] found in the Dingtao King Mausoleum during the Dynasty West Dynasty (206 BC-25 AC) revealed a massive degradation of the wooden objects. Determinations have shown that the degradation is caused by fungi. DNA sequencing of isolated fungi showed that there are 114 genres of fungi. However, in all samples, the most abundant genus was *Hypochnicium* sp., which represent 98.61–99.45%

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Wood objects exhibited in museums are subject to deterioration of biological agents. The wood Jesuit sculptures from South America exposed at the Museum of Natural Sciences of La Plata, Buenos Aires Argentina, are subject to the biodegradation [82]. Determinations made on a strip of degraded wood of the *Cedrela fissilis* species led to the identification of two fungi species*: Nigrospora sphaerica* and *Chaetomium globosum*. *Chaetomium* is a recognized macromycete for its ability to destroy wood, but for *Nigrospora sphaerica*, very few things are

**Figure 8.** Effect of inorganic nanomaterial with AgNPs, CuNPs, TiNPs, on some fungal and bacterial strain isolated from

**Figure 7.** Fungal species frequency (%) (micromycetes) identified on biodeteriorated wood artifacts, from Islamic Art

wood artifacts from Saqqara necropole. Concentration of nanoproduct applied: = 10 μg/mL [79].

Museum, Saqqara necropolis, Grand Egyptian Museum, Cheops Solar Boat [78].

of the total of the fungal community.


In vitro tests performed in order to establish the biological action of three types of inorganic nanomaterials with Ag, Ti, and Cu (AgNPs, CuNPs, TiNPs) on fungi and bacteria (*Bacillus alvei*, *Short Bacilli*, *Bacilli Spore Former*, *Aspergillus niger*, *Aspergillus flavus*, *Aspergillus fumigatus*) isolated from funerary masks of degraded wood from Saqqara showed that the most effective of the tested materials is AgNPs, followed by CuNPs and TiNPs [79], both for fungi and bacteria (**Figures 8** and **9**). The action mechanism of AgNP includes processes such as adherence to microbial cells, penetration into cells, free radical generation, DNA and RNA damage [79, 80].

**5. Microbial degradation of wood**

82 New Uses of Micro and Nanomaterials

The degradation of wood materials depends on physico-chemical and biological factors such as temperature, humidity, nutrients, and the type of wood (hardwood or softwood), specific to the environment in which they are exposed. Among the biological factors, insects, macro- and micromycetes, and bacteria, the microbial load of the environment, corroborated with humidity and temperature, plays an important role in the biodegradation processes of this material. Of the microbiological agents, the most common types of biodegradation are those caused by fungi and bacteria, which manage to degrade the wood through enzymatic mechanisms with the enzymes they are secreting. The fungi types that attack wood materials are divided into three classes:

**1.** White-root fungi can degrade all cellular components by using nonspecific enzymes that they secrete, but in a first stage, they degrade the lignin using hemicellulose as a carbon source. Following the degradation with these types of fungi, the attacked surfaces get a whitish appearance [75]. This class includes macromycetes such as *Phanerochaete chrysosporium* (*Sporotrichum pulverulentum*), *Phanerochaete sordida*, *Phlebia radiata*, and *Phlebia* 

**2.** Brown-root fungi generally degrade cellulose and hemicellulose from wood, but they also degrade lignin. The mechanisms used by brown rot fungi in the biodegradation of wood are both enzymatic and non-enzymatic. These micromycetes do not produce lignin degradation enzymes but have a mechanism that results in lignin modification and slow reduction of lignin content in the attacked wood. This class includes macromycete species as *Serpula lacrymans*, *Postia placenta*, *Gloeophyllum trabeum*, *and Tyromyces palustris*. Surfaces attacked by fungi of this class get a brownish look [77]. Studies on wood sample of *Pinus sylvestris* and *Populus euramericana* showed that after vacuum treatment with inorganic or organic preservatives, which contain Cr6+, Cu2+, As5+, organic salts of ammonia and N-alkylbenzyldimethylammonium chloride, inoculated with macromycetes from the species *S. lacrymans 1*, *S. lacrymans 2*, *P. placenta*, *G. trabeum*, *and T. palustris*, reveal a substantial reduction in wood loss due to the

**3.** Soft root fungi, or micromycetes, from which the most popular are *Penicillium chrysogenum* and *Aspergillus niger*, perform deterioration from edge to center of wood. In a study of wood artifacts from Islamic Art Museum, the Grand Egyptian Museum and Saqqara necropolis [78], two species of of the genus *Alternaria*, 15 species of *Aspergillus*, three species of the genus *Cladosporium*, six species of *Penicillium*, two species of *Trichophyton*, along with species of the genus *Cladosporium*, *Chaetomium*, *Phoma*, *Stemphylium*, *Ulocladium*, and *Syncephalastrum*, were found most of them with cellulolytic enzymatic activity, able to degrade the wood [78]. Their frequency on the analyzed artifacts was between 7.1 and 35.7%; the most common fungal species being (**Figure 7**) *Aspergillus. brasiliensis*, *Aspergillus flavus* var. columnaris, *Penicillium* sp.2, *Aspergillus parasiticus*, *Aspergillus terreus*, *Aspergillus versicolor*, *Cladosporium*

sp.1, *and Penicillium* sp.3, the rest being encountered at a frequency of 7.1% [78].

In vitro tests performed in order to establish the biological action of three types of inorganic nanomaterials with Ag, Ti, and Cu (AgNPs, CuNPs, TiNPs) on fungi and bacteria (*Bacillus alvei*, *Short Bacilli*, *Bacilli Spore Former*, *Aspergillus niger*, *Aspergillus flavus*, *Aspergillus fumigatus*)

and water.

*tremellosa* [76] which is able to degrade wood lignin to CO<sup>2</sup>

inhibition of the biological activity of the macromycetes tested [77].

Another study performed on China's degraded wood objects [81] found in the Dingtao King Mausoleum during the Dynasty West Dynasty (206 BC-25 AC) revealed a massive degradation of the wooden objects. Determinations have shown that the degradation is caused by fungi. DNA sequencing of isolated fungi showed that there are 114 genres of fungi. However, in all samples, the most abundant genus was *Hypochnicium* sp., which represent 98.61–99.45% of the total of the fungal community.

Wood objects exhibited in museums are subject to deterioration of biological agents. The wood Jesuit sculptures from South America exposed at the Museum of Natural Sciences of La Plata, Buenos Aires Argentina, are subject to the biodegradation [82]. Determinations made on a strip of degraded wood of the *Cedrela fissilis* species led to the identification of two fungi species*: Nigrospora sphaerica* and *Chaetomium globosum*. *Chaetomium* is a recognized macromycete for its ability to destroy wood, but for *Nigrospora sphaerica*, very few things are

**Figure 7.** Fungal species frequency (%) (micromycetes) identified on biodeteriorated wood artifacts, from Islamic Art Museum, Saqqara necropolis, Grand Egyptian Museum, Cheops Solar Boat [78].

**Figure 8.** Effect of inorganic nanomaterial with AgNPs, CuNPs, TiNPs, on some fungal and bacterial strain isolated from wood artifacts from Saqqara necropole. Concentration of nanoproduct applied: = 10 μg/mL [79].

**Figure 9.** Effect of inorganic nanomaterial with AgNPs, CuNPs, TiNPs, on some fungal and bacterial strain isolated from wood artifacts from Saqqara necropole. Concentration of nanoproduct applied: = 15 μg/mL [79].

known regarding its effects on wood [82]. Bacteria are another class of biological agents that can affect the structure of the wood. Thus, in studies conducted to find an optimal method of disinfection and protection of wood surfaces in the historical area of Auschwitz-Birkenau II, bacterial species such as *Pseudomonas fluorescens*, *Staphylococcus equorum,* and *Bacillus cereus* have been isolated from this site. In terms of fungi, the following species have been identified on the wood surfaces: *Alternaria alternata*, *Chaetomium globosum*, *Cladosporium cladosporioides*, *Engyodontium album*, and *Penicillium citreonigrum*.

In vivo tests, made on new pieces of white poplar wood, previously sterilized and treated with a mixture of cultures of bacteria and/or fungi, were aimed at the evaluation of the number of living microorganisms on the surfaces (bacteria) and the estimation of the percentage from the wood surface altered by fungal activity, as well as the changes in color and luminance of the treated samples. The study reveals that the best commercially available biocidal products are B, ABM-1, and R 101 (**Figure 10**) (product B containing 24% benzyl alkyl (C12–16) dimethylammonium chlorides, 5% boric acid ABM-1 contains N-3-aminopropyl-1,3-propanediamine, N,N-dialkyl (C10–C16)-N-methyl N-polyoxyethylene ammonium propionate, N,N-dialkyl (C10–C14) [3-dodecanoylamino)] propyl dimethyl ammonium acetate; product R101 contains 40–60% N,N-dodecyl-N,N-dimethylammonium chloride and 20–25% isopropanol). The best results were obtained for product R101, followed by AM-1, applied by spray or fogging exposure. The color (Δ*E*) and luminance (Δ*L*) tests showed that for the treatments chosen, no remarkable differences compared to the untreated control were observed (**Figure 11**). In another study, the effects of some aqueous dispersions of silver or zinc nanoparticles (AgNPs, ZnNPs) to air and liquid permeability of *Paulownia* wood samples exposed to *Trametes versicolor* were assessed [83]. The wood samples were heat treated at 100 and 150°C, after which they were exposed to *T. versicolor*. Permeability values were measured before and after exposure to fungal activity. The results obtained showed significant decreases in permeability in all treatments after exposure to fungi (**Figure 12**). The permeability difference was related to the growth and accumulation of fungal hyphae along the lumen vessels, which block the fluid transfer. The best results were obtained by heat treatment at 150°C, followed by impregnation

**Figure 11.** The color and luminance difference of wood samples after biocidic product applications. Δ*E* = difference of

**Figure 10.** Biocidal effect of some commercial products on the wood samples inoculated with fungal strains, by spraying

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**Figure 12.** Specific air permeability in wood samples treated with ZnNps and/or AgNps nanomaterials after exposure to

color; Δ*L* = difference of luminance [84].

or fogging [84].

action of rot-white fungus *Trametes versicolor* [83].

Polymeric Micro- and Nanosystems for Wood Artifacts Preservation http://dx.doi.org/10.5772/intechopen.79135 85

**Figure 10.** Biocidal effect of some commercial products on the wood samples inoculated with fungal strains, by spraying or fogging [84].

known regarding its effects on wood [82]. Bacteria are another class of biological agents that can affect the structure of the wood. Thus, in studies conducted to find an optimal method of disinfection and protection of wood surfaces in the historical area of Auschwitz-Birkenau II, bacterial species such as *Pseudomonas fluorescens*, *Staphylococcus equorum,* and *Bacillus cereus* have been isolated from this site. In terms of fungi, the following species have been identified on the wood surfaces: *Alternaria alternata*, *Chaetomium globosum*, *Cladosporium cladosporioides*,

**Figure 9.** Effect of inorganic nanomaterial with AgNPs, CuNPs, TiNPs, on some fungal and bacterial strain isolated from

wood artifacts from Saqqara necropole. Concentration of nanoproduct applied: = 15 μg/mL [79].

In vivo tests, made on new pieces of white poplar wood, previously sterilized and treated with a mixture of cultures of bacteria and/or fungi, were aimed at the evaluation of the number of living microorganisms on the surfaces (bacteria) and the estimation of the percentage from the wood surface altered by fungal activity, as well as the changes in color and luminance of the treated samples. The study reveals that the best commercially available biocidal products are B, ABM-1, and R 101 (**Figure 10**) (product B containing 24% benzyl alkyl (C12–16) dimethylammonium chlorides, 5% boric acid ABM-1 contains N-3-aminopropyl-1,3-propanediamine, N,N-dialkyl (C10–C16)-N-methyl N-polyoxyethylene ammonium propionate, N,N-dialkyl (C10–C14) [3-dodecanoylamino)] propyl dimethyl ammonium acetate; product R101 contains 40–60% N,N-dodecyl-N,N-dimethylammonium chloride and 20–25% isopropanol). The best results were obtained for product R101, followed by AM-1, applied by spray or fogging exposure. The color (Δ*E*) and luminance (Δ*L*) tests showed that for the treatments chosen, no remarkable differences compared to the untreated control were observed (**Figure 11**). In another study, the effects of some aqueous dispersions of silver or zinc nanoparticles (AgNPs, ZnNPs) to air and liquid permeability of *Paulownia* wood samples exposed to *Trametes versicolor* were assessed [83]. The wood samples were heat treated at 100 and 150°C, after which they were exposed to *T. versicolor*. Permeability values were measured before and after exposure to fungal activity. The results obtained showed significant decreases in permeability in all treatments after exposure to fungi (**Figure 12**). The permeability difference was related to the growth and accumulation of fungal hyphae along the lumen vessels, which block the fluid transfer. The best results were obtained by heat treatment at 150°C, followed by impregnation

*Engyodontium album*, and *Penicillium citreonigrum*.

84 New Uses of Micro and Nanomaterials

**Figure 11.** The color and luminance difference of wood samples after biocidic product applications. Δ*E* = difference of color; Δ*L* = difference of luminance [84].

**Figure 12.** Specific air permeability in wood samples treated with ZnNps and/or AgNps nanomaterials after exposure to action of rot-white fungus *Trametes versicolor* [83].

with ZnNps or AgNps which significantly inhibited the growth of the microorganism, reducing the mass loss of impregnated wood samples subjected to fungal attack [83].

**Conflict of interest**

**Author details**

Nicoleta Radu<sup>1</sup>

**References**

Bucharest, Romania

culher.2012.01.006

99-75-63-310-9

10.1007/s11998-016-9873-6

The author(s) declared no potential conflicts of interest.

Rodica-Mariana Ion1,2\*, Ramona-Marina Grigorescu<sup>1</sup>

\*Address all correspondence to: rodica\_ion2000@yahoo.co.uk

1 ICECHIM, Research Group "Evaluation and Conservation of Cultural Heritage",

2 Doctoral School of Materials Engineering, Valahia University, Targoviste, Romania

Chichester, West Sussx, UK. 2016. DOI: 10.1002/9781119106500

United States Department of Agriculture Forest Service; 2010

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[3] Salminen E, Valo R, Korhonen M, Jernlas R. Wood preservation with chemicals. Copenhagen, Denmark: Best Available Techniques (BAT) Nordic Council of Ministers; 2014

[4] Ghetiu MM, Toporet V. Chimia Lemnului. Chisinau: Ed. Tehnica-Info; 2010. ISBN: 978-

[5] Clausen CA. Biodeterioration of Wood. Madison, Wisconsin: Forest Products Laboratory,

[6] Ion R-M, Doncea S-M, Ţurcanu-Caruțiu D. Nanotechnologies in Cultural Heritage— Materials and Instruments for Diagnosis and Treatment. In: Kyzas G, editor. Novel

[7] Nkeuwa WN, Riedl B, Landry V. Transparent UV-cured clay/UV-based nanocomposite coatings on wood substrates: Surface roughness and effect of relative humidity on optical properties. Journal of Coatings Technology and Research. 2017;**14**(3):555-569. DOI:

[8] Nami Kartal S, Tenzi E, Yilmaz H, Goodell B. Bioremediation and decay of wood treated with ACQ, microionized ACQ, nano-CuO and CCA wood preservatives. International Biodeterioration & Biodegradation. 2015;**99**:95-101. DOI: 10.1016.j.ibiod.2015.01.004

Nanomaterials. IntechOpen; 2018. pp. 173-190. DOI: 10.5772/intechopen.71950

, Lorena Iancu1,2, Paul Ghioca1

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Regarding methods of treatment against wood degradation, there are currently several methods of protection against decomposition caused by biological agents. From these, organic compounds based on quaternary ammonium salts were the most used. Studies conducted to determine the antimicrobial activity of three biocides against *Pseudomonas fluorescens*, *Staphylococcus equorum*, *Bacillus cereus*, *Bacillus muralis*, *Sporosarcina aquimarina, Rhodococcus fascians*, and some fungi species such as *Chaetomium globosum*, *Penicillium citreonigrum*, *Cladosporium cladosporioides 1*, *Acremonium strictum*, *Aspergillus fumigatus* and *Cladosporium cladosporioides 2*, all isolated from wood or brick surfaces, showed that species such as *Staphylococcus equorum*, *Bacillus cereus*, *Sporosarcina aquimarina*, *Rhodococcus fascieni, Cladosporium cladosporioides*, and *Acremonium strictum* have a high susceptibility to quaternary ammonium biocides [85]. Thus, the wood objects with a historical value can be efficiently disinfected by three times application of a biocide (30% v/v) which contains dodecyl dimethyl ammonium chloride, citric acid, propiconazole, and propanol [85]. The mechanism of action of ammonium quaternary salts is based on the dissolution of certain sites from cell walls, which results in the loss of microbial cell integrity, followed by exposure of cell content and release of the material out of the cell, followed by degradation of proteins, of nucleic acids, and cell lysis, the latter caused by autolytic enzymes [85].

Protecting degradation of wood by biological agents can also be done without biocides based on quaternary ammonium salts. A wood protection variant is based on the application of a titanium isopropoxide gel and ammonium cerium nitrate as a stabilizer for wood treatment [86]. As a mechanism of action, it is assumed that the hydrolysis of titanium isopropoxide is initiated by the wood-based OH groups as well as by the moisture in the cellular wood wall resulting in a layer of cerium-doped TiO2 which seals the wood surface and thus limiting the direct exposure of micro- or nanopores of wood to fungal hydrolytic enzymes. Studies conducted on Norway spruce have shown that this method can be protected against degradation by biological agents such as *Gloeophyllum trabeum*, *Rhodonia placenta,* and *Coniophora puteana*.
