Water activity in subaerial microbial biofilms on stone monuments

Area of Science:

• Environmental microbiology
• Bio-deterioration
• Geomicrobiology

Background:

• Stone monuments host ubiquitous microbial communities despite harsh conditions and limited water access.
• Understanding water availability is critical for microbial survival and activity on stone surfaces.
• Direct measurement of water activity in subaerial biofilms (SABs) on stone is challenging.

Purpose of the Study:

• To determine factors controlling water activity in stone-dwelling microbial communities.
• To develop and apply a novel method for estimating water activity in SABs.
• To assess water activity dynamics on stone monuments over time.

Main Methods:

• A minimally invasive method combining conservative sampling, local weather data, confocal imaging, and mathematical modeling was developed.
• The methodology was applied to SABs on marble monuments (Federal Hall and Thomas Jefferson Memorials).
• Water activity was estimated over an approximately one-year period.

Main Results:

• Water activity in SABs is primarily constrained by local temperature and relative humidity.
• Community structure has a limited impact on water activity predictions.
• The developed method provides reliable estimations of water activity in situ.

Conclusions:

• Environmental factors (temperature, humidity) are the main drivers of water activity for stone-dwelling microbes.
• The novel methodology offers a practical approach for studying water relations in monument biofilms.
• This research provides insights into microbial survival strategies on historical stone structures.