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also Desulfobacteraceae, with Desulfofrigus (0.008 % in G5 and 0.0006 % in B4), Desulforhopalus (0.0006 % in B4) and unclassified genera (0.0009 % in G6, 0.003 % in B4 and 0.003 % in B6) (Greene, Patel and Yacob, 2009; Rosenberg et al., 2013).

      There is a strong link between the location and the occurrence of the nitrogen oxidizing and sulphur bacteria. Both are present in selected samples across both locations, but mainly in the City Hall of Ghent, where in one sample they even reach high abundance. There is also a link between the occurrence of the nitrifying and sulphur prokaryotes and the higher soluble salt content of respectively nitrate or sulphate. However, also here there are some exceptions. The occurrence of sulphate reducing bacteria followed the same trend. These bacteria can cause further deterioration (Krumbein and Gorbushina, 2009) but besides inducing gypsum crust formation, they can reduce the sulphate and precipitate calcium carbonate. This process also produces sulphur and H₂S (Castanier, Le Métayer-Levrel and Perthuisot, 1999). As one sample in the city (G5) contains both a high concentration of PNS and sulphate reducing bacteria, it is not impossible that both groups are strongly linked together.

      These results combine some of the findings of previous research by Mansch and Bock (1998) & Villa et al. (2015). The former found more nitrifying bacteria in the urban environment and the latter more sulphur oxidizing bacteria. It also confirms the findings of Li et al. (2016). However, members of sulphur compound oxidizing genera of which it is known that they deteriorate building stones, such as Thiobacillus (and related genera) have not been found (Krumbein and Gorbushina, 2009). This contrasts with the earlier findings of Villa et al. (2015). Furthermore, it is unclear if the PNS bacteria would affect natural building stones the same way as Thiobacillus. The presence of sulphur bacteria that only tolerate lower amounts of sulphur can be related to the decreasing SO₂ concentrations in the atmosphere. The low abundance of sulphur and nitrogen oxidizers, combined with the absence of those groups in several samples, indicates that other chemical factors are most likely still dominating gypsum crust formation. Although those gypsum crust have been formed since decades, when the SO₂ and NO_x concentrations were higher, it cannot be excluded that back then more sulphur and nitrogen oxidizers were present affecting crust formation.

      Besides the metagenomic approach, also an isolation campaign has been performed. This did not succeed to retrieve chemolithoautotrophic prokaryotes. However, 20 genera belonging to 31 species of heterotrophic bacteria were successfully isolated and identified. Growth occurred mainly aerobic and denitrification occurred barely. Many isolates contained a red, orange, pink or yellow pigment and one of them, Arthrobacter agilis, has been successfully applied on the water run-off test (Figure 2). After one cycle of two hours, the rocks became significantly red and this has been confirmed by the spectrophotometric data. There was a dip between 450 and 560 nm in the reflectance, leading to an increase visibility of the complementary 99red/orange colours. During this test, we applied bacterial concentrations that do not occur in nature. However, it shows how easy it can discolour a natural building stone and the potential of some of the bacteria to cause aesthetic changes. Besides natural oxidation of iron-bearing minerals, these bacteria could also contribute to the rusty/red colour on the Castle of Berlare.

      Figure 2: A) Spectral data showing the initial state of the Savonnières limestone (blank) and the progress of the colour change after adding Arthrobacter agilis during the different cycles (Cycle 1–3). B) Savonnières stone after three cycles showing the discolouration compared to the initial state at the top section.

       Conclusion

      Lede stone at Ghent and Berlare were both deteriorated and contained gypsum crusts. The crusts were more elaborate in Ghent with overall a higher content of soluble salts. 16S rRNA gene amplicon sequencing revealed potential stone deteriorating nitrogen and sulphur prokaryotes, especially on the City Hall. This suggests a positive correlation with air pollution. However, they were only present with a low concentration in some samples and absent in the isolates. Currently, a strong effect of prokaryotes on crust formation is not expected. Furthermore with decreasing sulphur pollutions, the gypsum is mainly a result of historical accumulation. on Lede stone, prokaryotes can have an impact on the appearance of the monuments as Arthrobacter agilis successfully discoloured Savonnières limestone.

       Acknowledgements

      This work was funded by Research Foundation Flanders (Research grant number 11D4518N). We would like to thank Sarah Williamson and the lab technicians of CMET for their help with the experiments.

       References

      Bai, Y., Thompson, G. E. and Martinez-Ramirez, S. (2006) ‘Effects of NO2 on oxidation mechanisms of atmospheric pollutant SO 2 over Baumberger sandstone’, Building and Environment, 41(4), pp. 486–491. doi: 10.1016/j.buildenv.2005.02.007.

      Bionda, D. (2005) RUNSALT – A graphical user interface to the ECOS thermodynamic model for the prediction of the behaviour of salt mixtures under changing climate conditions. Available at: http://science.sdf-eu.org/runsalt.

      Camuffo, D., Del Monte, M. and Sabbioni, C. (1983) ‘Origin and growth mechanisms of the sulfated crusts on urban limestone’, Water, Air, and Soil Pollution. Kluwer Academic Publishers, 19(4), pp. 351–359. doi: 10.1007/BF00159596.

      Castanier, S., Le Métayer-Levrel, G. and Perthuisot, J.-P. (1999) ‘Ca-carbonates precipitation and limestone genesis — the microbiogeologist point of view’, Sedimentary Geology, 126(1–4), pp. 9–23. doi: 10.1016/S0 037-0738(99)00028-7.

      Dewanckele, J. et al. (2014) ‘Neutron radiography and X-ray computed tomography for quantifying weathering and water uptake processes inside porous limestone used as building material’, 100Materials Characterization. Elsevier Inc., 88, pp. 86–99. doi: 10.1016/j.matchar.2013.12.007.

      Doehne, E. and Price, C. A. (2010) Stone Conservation, An Overview of Current Research. 2nd ed. Re. Los Angeles, CA: Getty Conservation Institute.

      Greene, A. C., Patel, B. K. C. and Yacob, S. (2009) ‘Geoalkalibacter subterraneus sp. nov., an anaerobic Fe(III)- and Mn(IV)-reducing bacterium from a petroleum reservoir, and emended descriptions of the family Desulfuromonadaceae and the genus Geoalkalibacter’, INTERNATIONAL JOURNAL OF SYSTEMATIC AND EVOLUTIONARY MICROBIOLOGY, 59(4), pp. 781–785. doi: 10.1099/ijs.0.001537-0.

      Hunter, C. N. et al. (eds) (2009) The Purple Phototrophic Bacteria, Photosynthetica. Dordrecht: Springer Netherlands (Advances in Photosynthesis and Respiration). doi: 10.1007/978-1-4020-8815-5.

      De Kock, T. et al. (2015) ‘Lede Stone: A potential “Global Heritage Stone Resource” from Belgium’, Episodes, 38(2), pp. 91–96. doi: Скачать книгу