The tombstones at the Monumental Cemetery of Milano select for a specialized microbial community

Michela Gambino,Gloria Lepri,Adam Štovícek,Lusine Ghazayarn,Federica Villa,Osnat Gillor,Francesca Cappitelli

doi:10.1016/j.ibiod.2021.105298

Abstract

Subaerial biofilms play a central role in the ecology and biodeterioration of many outdoor monuments and pieces of art. It is well established that microorganisms can face a broad range of stress by living in these subaerial environments, but their origin, taxa determinants and physiological traits are debated. Here, we hypothesized that the bacteria forming these biofilms originate from the surrounding air and soil and that the selective pressure of a life on rocks shapes the community. To verify this hypothesis, we studied the microbial communities of nine tombstones of the Monumental Cemetery of Milano, by collecting samples in three seasons. We analyzed the structure of these subaerial biofilms, compared them with the bacteria identified in the surrounding air and soil and found that only few rare taxa are shared among the three compartments and have been selected by the stone environment. In addition, we considered which parameters - among temperature, humidity, light, season and lithotype - concur to structure the microbial community.

Highlights

The interface between air and rocks is an ancient and ubiquitous habitat supporting subaerial microbial growth as biofilms (Costerton and Woodely 2003; Gorbushina and Broughton2009)
Temperature ranged between 23 C and 30 C with 17% to 36 % relative humidity (RH); during summer, temperature ranged between 31 C and 35 C with 43% to 51 % RH; during winter, temperature ranged between 14 C and 21 C with 22% to 36 % RH
Our analysis clearly shows that the tombstones microbial communities are very different from the microorganisms in the surrounding soil and air, irrespectively of the stone lithotype or the season of the sampling campaign

Summary

Introduction

The interface between air and rocks is an ancient and ubiquitous habitat supporting subaerial microbial growth as biofilms (Costerton and Woodely 2003; Gorbushina and Broughton2009). Rocks surface offers very little shelter - just pores and cracks in the stone surface – exposing these microorganisms to UV and dramatic temperature changes (Walker and Pace 2007). In response to these stressful conditions, microorganisms on rocks typically grow as a wellorganized multispecies community protected by a matrix of exopolymeric substances (Gorbushina 2007). It has been shown that the permeability, the mineral composition and the texture of a rock, as well as its surface geometry and the degree of shading, shape the structure and the composition of these microbial communities

Methods

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Discussion

Conclusion