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Natural stones are essential for our built heritage. They are considered durable and permanent. However, they deteriorate through physical, chemical and biological action with water as the principal facilitator. Within a stone, water transport and retention depend on the stone's characteristics. It is expected that biofilms and extracellular polymeric substances change these properties and thus the water-stone relationship. To study the effect of the biofilms, three porous natural building stones: Ernzen, Euville and Savonnières, were biofouled with cyanobacteria Phormidium autumnale. The amount of biofilm was estimated by spectrophotometry, characterized by optical microscopy, and (environmental) scanning electron microscopy. Water transport and retention for biofouled and untreated samples were determined following European standards. Microscopy showed that the biofilms primarily covered the stone's outer surface. They experienced swelling and shrinkage dependent on the subjected relative humidity conditions, which could facilitate physical weathering. The biofilms slightly affected the water transport properties and induced a (near) hydrophobic surface. They reduced the drying rate and capillary coefficient. Moreover, biofouled samples absorbed more water vapor, had a higher water content, while no direct effect was measured on the water vapor diffusion and gas permeability. These changes could affect future weathering processes, including freeze-thaw and salt weathering.

Microbial communities are responsible for biological wastewater treatment, but our knowledge of their diversity and function is still poor. Here, we sequence more than 5 million high-quality, full-length 16S rRNA gene sequences from 740 wastewater treatment plants (WWTPs) across the world and use the sequences to construct the ‘MiDAS 4’ database. MiDAS 4 is an amplicon sequence variant resolved, full-length 16S rRNA gene reference database with a comprehensive taxonomy from domain to species level for all sequences. We use an independent dataset (269 WWTPs) to show that MiDAS 4, compared to commonly used universal reference databases, provides a better coverage for WWTP bacteria and an improved rate of genus and species level classification. Taking advantage of MiDAS 4, we carry out an amplicon-based, global-scale microbial community profiling of activated sludge plants using two common sets of primers targeting regions of the 16S rRNA gene, revealing how environmental conditions and biogeography shape the activated sludge microbiota. We also identify core and conditionally rare or abundant taxa, encompassing 966 genera and 1530 species that represent approximately 80% and 50% of the accumulated read abundance, respectively. Finally, we show that for well-studied functional guilds, such as nitrifiers or polyphosphate-accumulating organisms, the same genera are prevalent worldwide, with only a few abundant species in each genus., Nature Communications, 13, ISSN:2041-1723

Microorganisms, including bacteria, archaea, algae and fungi, colonize natural building stones. Bacteria are among the most relevant colonizers, as they impact substrates in multiple forms, primarily attributed to their high diversity. They alter rock properties, induce discoloration, dissolution or precipitation, which can lead to degradation over time or in some cases, protection. Numerous studies suggested a link between rock alteration and bacteria, although there are still inconclusive conclusions. Moreover, the role of archaea remains unresolved. Classical cultivation techniques capture a fraction of bacterial and archaeal diversity. Recently, culture-independent and omics-technologies provide tools to further understand their full diversity and true role. Based on field and experimental work, this comprehensive review provides an overview of biocolonization and potential changes during the 21st Century. To better understand the role of bacteria and archaea, the focus will be on their capabilities to alter natural building stones. It also includes a short overview of methods to understand the processes and dynamics of biocolonization. The conclusions of this work will not only improve our understanding of deterioration in general, but it can also make sustainable biorestoration with bacteria the preferred choice instead of chemical and physical agents.