Influence of Environment on Microbial Colonization of Historic Stone Buildings with Emphasis on Cyanobacteria

Christine C. Gaylarde

doi:10.3390/heritage3040081

Abstract

Microbial cells that produce biofilms, or patinas, on historic buildings are affected by climatic changes, mainly temperature, rainfall and air pollution, all of which will alter over future decades. This review considers the colonization of stone buildings by microorganisms and the effects that the resultant biofilms have on the degradation of the structure. Conservation scientists require a knowledge of the potential effects of microorganisms, and the subsequent growth of higher organisms such as vascular plants, in order to formulate effective control strategies. The vulnerability of various structural materials (“bioreceptivity”) and the ways in which the environmental factors of temperature, precipitation, wind-driven rain and air pollution influence microbial colonization are discussed. The photosynthetic microorganisms, algae and cyanobacteria, are acknowledged to be the primary colonizers of stone surfaces and many cyanobacterial species are able to survive climate extremes; hence special attention is paid to this group of organisms. Since cyanobacteria require only light and water to grow, can live endolithically and are able to survive most types of stress, they may become even more important as agents of stone cultural property degradation in the future.

Highlights

There may be direct results on the materials used in construction, but environmental factors influence the microorganisms in the surroundings, and these can cause weathering
Gaylarde and Gaylarde [42], analyzing microbial biofilms from a wide variety of buildings with different surfaces and in various parts of the world, showed that cyanobacteria, were the most frequent major biomass on Latin American buildings composed of stone or composites, with an average 66.1% of total biomass, followed by fungi (17.7%) and algae (12.9%), while in Europe algae were most common at 46.32% total biomass, followed by cyanobacteria (35.2%)
Potential Effects of Climate Change. It is obvious from the effects of climate on microbial biofilms discussed in the above section that climate change will affect the degradation of historic properties caused by microorganisms, even though the subaerial biofilm is a complex consortium and able to overcome many types of environmental stress [52]

Summary

Introduction

Climate change is an established fact. Global temperatures, precipitation, wind patterns and other weather phenomena are altering. As the stone weathers its surface will change because of environmental effects; physical and chemical actions will almost certainly increase the roughness of the surface, for instance, while the formation of the initial biofilm may either increase or decrease vulnerability to further colonization, depending on factors such as species present and whether large quantities of extracellular polymeric materials, which act as glues, are produced by the sessile cells. The first organisms to colonize a stone surface to produce the so-called “subaerial biofilms” [13] are those that do not require organic foodstuffs - the phototrophic algae and cyanobacteria (see, for example, [14,15,16]) Autotrophic bacteria, such as those that utilize inorganic nitrogen or sulfur as energy sources, may colonize at this time. As the stone surface breaks down to form a “protosoil”, it becomes susceptible to the deposition and growth of spores and seeds from other, higher, organisms, leading to the formation of the typical overgrown appearance of neglected historic properties

Deterioration of Stone Buildings by Microorganisms

Effect of Air Pollution

Potential Effects of Climate Change

Findings

Conclusions