Life on the rocks

Abstract

SummaryBiofilms are interface micro-habitats formed by microbes that differ markedly from those of the ambient environment. The term 'subaerial biofilm' (SAB) was coined for microbial communities that develop on solid mineral surfaces exposed to the atmosphere. Subaerial biofilms are ubiquitous, selfsufficient, miniature microbial ecosystems that are found on buildings, bare rocks in deserts, mountains, and at all latitudes where direct contact with the atmosphere and solar radiation occurs. Subaerial biofilms on exposed terrestrial surfaces are characterized by patchy growth that is dominated by associations of fungi, algae, cyanobacteria and heterotrophic bacteria. Inherent subaerial settlers include specialized actinobacteria (e.g. Geodermatophilus), cyanobacteria and microcolonial fungi. Individuals within SAB communities avoid sexual reproduction, but cooperate extensively with one another especially to avoid loss of energy and nutrients. Subaerial biofilm metabolic activity centres on retention of water, protecting the cells from fluctuating environmental conditions and solar radiation as well as prolonging their vegetative life. Atmospheric aerosols, gases and propagatory particles serve as sources of nutrients and inoculum for these open communities. Subaerial biofilms induce chemical and physical changes to rock materials, and they penetrate the mineral substrate contributing to rock and mineral decay, which manifests itself as bio-weathering of rock surfaces. Given their characteristic slow and sensitive growth, SAB may also serve as bioindicators of atmospheric and/or climate change.

Investigating the role of microbes in mineral weathering: Nanometre-scale characterisation of the cell–mineral interface using FIB and TEM

“…Cyanobacteria are photosynthetic oxygen-evolving bacteria distributed in many environments worldwide (Madigan et al, 2003), including surfaces and internal spaces of rocks (Gorbushina, 2007). It is known that cyanobacteria are capable of the alteration of some calcium containing minerals (Garcia-Pichel, 2006;Garcia-Pichel et al, 2010), however despite their common presence on rock surfaces in natural environments their potential role in silicate mineral weathering and nutrient release is at present poorly understood.…”

Rock-eating mycorrhizas: their role in plant nutrition and biogeochemical cycles

“…This review discusses the results of that programme in the framework of the increased interest in EcM fungi as ecosystem engineers notably through interactions with soil minerals. We do not intend to review the field of mineral weathering by fungi, because several important reviews have appeared in the last few years (Hoffland et al 2004;Wallander and Hagerberg 2004;Smits 2006;Wallander 2006;Gadd 2007;Gorbushina 2007). In this review we concentrate on the role of EcM fungal-mediated release of cations (K, Mg) and their role in alleviating aluminium toxicity and transport of Al in podzols.…”

The roles of endolithic fungi in bioerosion and disease in marine ecosystems. I. General concepts

“…However, it is now known that they have a significant presence in locations not usually regarded as prime fungal habitats, e.g. acid mine drainage, deep aquatic sediments, hydrothermal vents and the igneous oceanic crust (Reitner et al 2006; Gorbushina 2007; Vázquez-Campos et al 2014; Iversson et al 2016). In such locations, fungi may exist in symbiosis with chemolithotrophic prokaryotes (Ivarsson et al 2016).…”

“…These do not exhibit the filamentous hyphal mode of growth but produce unicellular yeast-like and microcolonial growth, occurring as small black melanised colonies resulting in dark brown to black discolouration on colonised surfaces (Marvasi et al 2012). This growth habit confers a high degree of resistance to environmental stress (Gorbushina 2007). Fungi, including lichens, can be epilithic (surface dwellers) and/or endolithic (interior dwellers) with cryptoendoliths occupying structural cavities, chasmoendoliths inhabiting fissures and cracks and euendolithic forms capable of active rock penetration (Cockell and Herrera 2008; Wierzchos et al 2012).…”

“…This appears to result from mechanical destruction caused by cell turgor pressure and extracellular polysaccharide production rather than the acid dissolution caused by many other fungi (Marvasi et al 2012). These fungi may also form casual mutualistic associations with algae in rock crevices (Gorbushina 2007). …”