Bioweathering Potential of Cultivable Fungi Associated with Semi-Arid Surface Microhabitats of Mayan Buildings

Abstract

Soil and rock surfaces support microbial communities involved in mineral weathering processes. Using selective isolation, fungi were obtained from limestone surfaces of Mayan monuments in the semi-arid climate at Yucatan, Mexico. A total of 101 isolates representing 53 different taxa were studied. Common fungi such as Fusarium, Pestalotiopsis, Trichoderma, and Penicillium were associated with surfaces and were, probably derived from airborne spores. In contrast, unusual fungi such as Rosellinia, Annulohypoxylon, and Xylaria were predominantly identified from mycelium particles of biofilm biomass. Simulating oligotrophic conditions, agar amended with CaCO3 was inoculated with fungi to test for carbonate activity. A substantial proportion of fungi, in particular those isolated from mycelium (59%), were capable of solubilizing calcium by means of organic acid release, notably oxalic acid as evidenced by ion chromatography. Contrary to our hypothesis, nutrient level was not a variable influencing the CaCO3 solubilization ability among isolates. Particularly active fungi (Annulohypoxylon stygium, Penicillium oxalicum, and Rosellinia sp.) were selected as models for bioweathering experiments with limestone-containing mesocosms to identify if other mineral phases, in addition to oxalates, were linked to bioweathering processes. Fungal biofilms were seen heavily covering the stone surface, while a biomineralized front was also observed at the stone-biofilm interface, where network of hyphae and mycogenic crystals was observed. X-ray diffraction analysis (XRD) identified calcite as the main phase, along with whewellite and wedellite. In addition, lower levels of citrate were detected by Attenuated Total Reflectance-Fourier-Transform Infrared Spectroscopy (ATR-FTIR). Overall, our results suggest that a diverse fungal community is associated with limestone surfaces insemi-arid climates. A subset of this community is geochemically active, excreting organic acids under quasi-oligotrophic conditions, suggesting that the high metabolic cost of exuding organic acids beneficial under nutrient limitation. Oxalic acid release may deteriorate or stabilize limestone surfaces, depending on microclimatic dynamics.

Biodegradative potential of fungal isolates from sacral ambient: In vitro study as risk assessment implication for the conservation of wall paintings

“…isolated from variously coloured patinas of the Catacombs of St. Callistus and Priscilla in Rome (Italy) were the only fungi able to dissolve calcite when cultured on CaCO 3 glucose agar, while all Aspergillus and Penicillium isolates tested negative [ 27 ]. Compared to all previous research, a recent work of Ortega-Morales et al [ 36 ] showed the greatest percentage of fungi able to dissolve calcite, with more than 59% of fungi isolated from surface microhabitats of Mayan buildings testing positive when cultured on CMEA and CR2A-A selective media. As these two agarized nutrient media vary in composition with respect to the CaCO 3 glucose agar used, fungal carbonate solubilization activity presumably depends not only on environmental factors and origin of the isolates, but on available sources of carbon and nitrogen as well.…”

“…Albertano and Urzì [ 27 ] suggested that microfungi colonizing marble and limestone monuments use nutrients produced by phototrophic microorganisms to synthesize organic acids which dissolve CaCO 3 from the substrate. According to Sterflinger [ 32 ] and Ortega-Morales et al [ 36 ], only fungi that produce and secrete acids can dissolve CaCO 3 , and strong oxalic acid (C 2 H 2 O 4 ) is the main “culprit” in most instances. Since organic acids are synthesized, as a by-product of oxidative metabolism during primary fungal metabolism, it is no wonder that in our study and many others as well [ 9 , 34 , 36 ], a transparent zone of CaCO 3 dissolution was formed very early, i.e., during the first week of the incubation period.…”

Lichens Bite the Dust – A Bioweathering Scenario in the Atacama Desert

“…Consequently, the alteration and transformation of the lithomatrix by metabolism and bioweathering processes of phototrophs can be expected ( Weber et al., 2011 ). This was described for extreme habitats such as Antarctica or ancient Mayan buildings ( Ortega-Morales et al., 2016 ) and similar interactions are very likely to occur in the Atacama Desert, but reports are still missing. Single processes of biogeophysical and biogeochemical weathering by (cyano-)bacteria, green algae, lichens, and fungi are well studied (reviewed in Salvadori and Municchia, 2016 ; Chen et al., 2000 ).…”

Strategies for14C Dating the Oxtotitlán Cave Paintings, Guerrero, Mexico

“…Oxalate-rich coatings occur globally and have been identified at a multitude of rock art sites, usually via chemical studies of rock paints. There is considerable evidence that oxalates in rock coatings are biogenic, the byproduct of bacteria (Bonaventura et al 1999; Hess et al 2008; Rusakov et al 2015), fungi (Gadd et al 2014; Monte 2003; Ortega-Morales et al 2016), lichens (Del Monte and Sabbioni 1987; Russ et al 1996), and mixed microbial communities (Gorbushina 2007). Evidence suggests that all carbon in oxalate biofilms originates from atmospheric carbon dioxide (Beazley et al 2002) and that, once formed, there is no carbon exchange with the substrate (Watchman 1993).…”