Wanfu Wang

The community distribution of bacteria and fungi on ancient wall paintings of the Mogao Grottoes

In this study, we compared the microbial communities colonising ancient cave wall paintings of the Mogao Grottoes exhibiting signs of biodeterioration. Ten samples were collected from five different caves built during different time periods and analysed using culture-independent and culture-dependent methods. The clone library results revealed high microbial diversity, including the bacterial groups Firmicutes, Proteobacteria, Actinobacteria, Acidobacteria, Cyanobacteria, Bacteroidetes, Gemmatimonadetes, Planctomycetes, and Chloroflexi and the fungal groups Euascomycetes, Dothideomycetes, Eurotiomycetes, Sordariomycetes, Saccharomycetes, Plectomycetes, Pezizomycetes, Zygomycota, and Basidiomycota. The bacterial community structures differed among the samples, with no consistent temporal or spatial trends. However, the fungal community diversity index correlated with the building time of the caves independent of environmental factors (e.g., temperature or relative humidity). The enrichment cultures revealed that many culturable strains were highly resistant to various stresses and thus may be responsible for the damage to cave paintings in the Mogao Grottoes.

Diversity and seasonal dynamics of airborne bacteria in the Mogao Grottoes, Dunhuang, China

The aim of this study was to analyze the phylogenetic composition of the bacterial community in the air at the Mogao Grottoes (Dunhuang, China) using a culture-dependent molecular approach. The 16S rRNA genes were amplified directly from the isolates with universally conserved and bacteria-specific rRNA gene primers. The PCR products were screened by restriction fragment length polymorphism, and representative rRNA gene sequences were determined and sequenced. A total of 19 bacteria genera were identified among 49 bacterial sequence types. Phylogenetic sequence analyses revealed high diversity within the bacterial community. The most predominant bacteria were Janthinobacterium (14.91%), Pseudomonas (13.40%), Bacillus (11.25%), Sphingomonas (11.21%), Micrococcus (10.31%), Microbacterium (6.92%), Caulobacter (6.31%), and Roseomonas (5.85%). The composition of bacterial communities differed greatly between different sites and at different times. The distribution of various bacteria was mainly affected by climatic parameters and human activities. These findings suggested that the opening of this cultural heritage site to visitors should be controlled and that maintaining the cave’s natural climatic conditions would aid the conservation and management of the grottoes’ paintings.

The microbial community characteristics of ancient painted sculptures in Maijishan Grottoes, China

In this study, a culture-independent Illumina MiSeq sequencing strategy was applied to investigate the microbial communities colonizing the ancient painted sculptures of the Maijishan Grottoes, a famous World Cultural Heritage site listed by UNESCO in China. Four mixed samples were collected from Cave 4–4 of the Maijishan Grottoes, the so-called Upper Seven Buddha Pavilion, which was built during the Northern Zhou Dynasty (557-581AD). The 16/18S rRNA gene-based sequences revealed a rich bacterial diversity and a relatively low fungal abundance, including the bacterial groups Actinobacteria, Acidobacteria, Bacteroidetes, Cyanobacteria, Chloroflexi, Firmicutes, Proteobacteria and Verrucomicrobia and the fungal groups Ascomycota, Basidiomycota and Chytridiomycota. Among them, the bacteria genera of Pseudonocardia and Rubrobacter and unclassified fungi in the order of Capnodiales were dominant. The relative abundance of Pseudonocardia in the painted layer samples was higher than that in the dust sample, while Cyanobacteria dominated in the dust sample. Many of them have been discovered at other cultural heritage sites and associated with the biodeterioration of cultural relics. The presence and activity of these pioneering microorganisms may lead to an unexpected deterioration of the painted sculptures that are preserved in this heritage site. Thus, proper management strategies and potential risk monitoring should be used in the Maijishan Grottoes to improve the conservation of these precious painted sculptures.

The sand-deposition impact of artificial gravel beds on the protection of the Mogao Grottoes

Gravel beds can prevent sand-dust emission and weaken sand-dust flux. We used wind-tunnel experiments and field observations on artificial gravel beds above the Mogao Grottoes to quantify their impact. In the report, we identified a significant correlation between gravel roughness and its ability to trap wind-transported sand. The optimal combinations of gravel diameter and coverage were determined. The greatest roughness is achieved when small gravel coverage is 75%, medium 40% and large 45%. We found that initial wind speed and gravel coverage are the key factors controlling the amount of sand trapped by the gravel beds.

Advancement and Prospect of Bionic Techniques in the Conservation of the Cultural Heritage

The ancient wall paintings and earthen architecture ruins are the most important part of cultural heritage. Inhabitation and locomotion of animals are major factors that lead to biodegradation and biodeterioration at the cultural heritage sites. In this miniview, based on our team work of cultural relics conservation in recent years, the latest findings domestic and overseas in fields of ethology and bionics were summarized, focusing on the correlated methods and techniques that can be used into cross-over study of cultural relics conservation. Animals biting, nesting, cocooning, crawling, and scratching are all behavioral process that easily bring damage to cultural heritage, such as ancient murals, architectures, earth ruins and so on. Both modern video record techniques and animal motion trajectory analysis may be taken use to improve the analytic accuracy of gait information for animals that crawling on the surface of cultural relics, which promoted the related study of motor pattern, behavior process, and damage pattern of animals to cultural relics. The three dimensional tiny force sensor with high resolution can be used for measuring normal adhesive force and tangential friction force of animals that contacted the surface of fragile cultural relics, which make animal adhesion modeling and historical relics mechanical model constructing possible, and provide newly evidence for biomechanics process illumination of animals locomotion. Totally, the application of the bionic techniques to the study of animals behavioral characteristics will provide new opportunity to better clarify the biological damaging mechanisms of cultural relics and control animal bioderioration, which will drive the development of cultural relics conservation technology in the near future.

The effects of atmospheric moisture on the mural paintings of the Mogao Grottoes

The aim of this paper is to study the influence of atmospheric humidity and temperature on the mural paintings in the Mogao Grottoes of Dunhuang by measuring the weight of a simulated mural block. Under open conditions, the daily changes in the atmospheric humidity and temperature have an apparent effect on the water content of these murals. There exists an obvious water exchange between atmosphere and mural, that is, there is a ±43 g m−2 moisture absorption–desorption ‘breathing’ process between the two. Evapotranspiration from the tree-belt, precipitation, and extremely dry weather also have an effect on the moisture associated with a mural painting. If the cave is closed, a comparable study finds that closure can make the effects of temperature and humidity changes disappear. The mural water content in this case remains stable and the harm due to water-salt deterioration is greatly reduced. Under closed conditions, artificial condensation dehumidification and control of the caves temperature and humidity stabilizes water activity in the mural paintings very effectively. This is a clear indication of the future steps required to protect the caves cultural relics.

Water in the Mogao Grottoes, China: where it comes from and how it is driven

The Dunhuang Mogao Grottoes in China was designated as a world heritage site by UNESCO in 1987 and is famous for its cultural relics. Water is the most active factor that harms the relics in the caves as it damages the grotto murals and painted sculptures. Thus, determining the water sources and driving forces of water movement is a key issue for protecting these cultural relics. These issues have troubled relics protectors for a long time. In this study, the authors chose a representative cave in the Mogao Grottoes and, by completely sealing the cave to make a closed system, measured the water vapor from the surrounding rock. This was accomplished by installing a condensation-dehumidification temperature-humidity control system for the collection of water vapor. The results show that there is continuous evaporation from the deep surrounding rock into the cave. The daily evaporation capacity is determined to be 1.02 g/(d·m2). The water sources and driving forces of water movement were further analyzed according to the character of the water evaporation and by monitoring the temperature and humidity of the surrounding rock. It was found that the water vapor in the cave derives from phreatic water. Moreover, the yearly fluctuation of temperature in the surrounding rock and geothermal forces are the basic powers responsible for driving phreatic evaporation. Under the action of the yearly temperature fluctuations, decomposition and combination of bound water acts as a “pump” that drives phreatic water migration and evaporation. When the temperature rises, bound water decomposes and evaporates; and when it falls, the rock absorbs moisture. This causes the phreatic water to move from deep regions to shallow ones. Determining the source and dynamic foundation of the water provides a firm scientific basis for protecting the valuable cultural relics in the caves.

Correction: The microbial community characteristics of ancient painted sculptures in Maijishan Grottoes, China

[This corrects the article DOI: 10.1371/journal.pone.0179718.].

Description of Naumannella cuiyingiana sp. nov., isolated from a ca. 1500-year-old mural painting, and emended description of the genus Naumannella

Strain AFT2T was isolated from a mural painting sample from a ca. 1500-year-old tomb located in Shanxi Province, China. The isolate was a Gram-stain-positive, non-motile, non-spore-forming, aerobic and oval to short-rod-shaped bacterium that formed white-pigmented colonies. Phylogenetic analyses based on 16S rRNA gene sequence revealed that strain AFT2T was most closely (97.01 %) correlated and formed a monophyletic clade with Naumannella halotolerans WS4616T (=DSM 24323T). The G+C content of the genomic DNA was 71.97 mol%, and the strain showed 37.27 % DNA-DNA relatedness to N. halotolerans DSM 24323T. The major cellular fatty acid was anteiso-C15 : 0 (55.32 %), and MK-9(H4) was the only respiratory quinone. The polar lipids comprised phosphatidylglycerol, diphosphatidylglycerol, two unknown phospholipids and five unknown glycolipids. ll-Diaminopimelic acid was detected in the cell-wall peptidoglycan (type A3γ), and the whole-cell sugars consisted of ribose, mannose, arabinose and galactose. On the basis of its phenotypic and phylogenetic characteristics, it is proposed that strain AFT2T should be classified as a representative of a novel species of the genus Naumannella, for which the name Naumannella cuiyingiana sp. nov. is proposed. The type strain is AFT2T (=CCTCC AB 2015428T=DSM 103164T).

Ecological Significance of the Sand Wedge In the Extra-Arid Gobi Area

The sand wedge was widely found, by field survey, to lie within the Gobi on the top of the Mogao Grottoes. The characteristics of its shape, size, structure, and ecological function were investigated. This original sand wedge was of a special type; formed in an arid environment, and with a multi-level fractal structure. The width range of main wedge was from 30 to 60 cm and its depth was about 50 cm, where the width of the irregular polygon matrix was about 60 to 160 cm. Meanwhile, the features of this sand wedge, including mechanical composition, salinity, and water content differed greatly from its matrix. The salt content in the sand wedge was 0.86 g · kg−1, correspondingly, that of the matrix reached 4.56 g · kg−1. The sand wedge can absorb plentiful rainfall and retain it for a long time, which can benefit plant survival. However, the higher salt content of the matrix would dissolve under eluviation, which plays an important role in pruning roots. These double functions of higher water content in the wedge and salt pruning in the matrix have made the main roots of vegetation grow inside the sand wedge only. Thus, the net shape structure of sand wedge was vital to vegetation distribution in the Gobi and the formation of the associated geomorphologic landscape. At the same time, the sand wedge formed a crucial habitat for small animals, thus was the last surviving such enclave in the extreme aridity of the Gobi ecosystem.