title: Is there a common water-activity limit for the three domains of life?
abstract: Archaea and Bacteria constitute a majority of life systems on Earth but have long been considered inferior to Eukarya in terms of solute tolerance. Whereas the most halophilic prokaryotes are known for an ability to multiply at saturated NaCl (water activity (a(w)) 0.755) some xerophilic fungi can germinate, usually at high-sugar concentrations, at values as low as 0.650-0.605 a(w). Here, we present evidence that halophilic prokayotes can grow down to water activities of <0.755 for Halanaerobium lacusrosei (0.748), Halobacterium strain 004.1 (0.728), Halobacterium sp. NRC-1 and Halococcus morrhuae (0.717), Haloquadratum walsbyi (0.709), Halococcus salifodinae (0.693), Halobacterium noricense (0.687), Natrinema pallidum (0.681) and haloarchaeal strains GN-2 and GN-5 (0.635 a(w)). Furthermore, extrapolation of growth curves (prone to giving conservative estimates) indicated theoretical minima down to 0.611 aw for extreme, obligately halophilic Archaea and Bacteria. These were compared with minima for the most solute-tolerant Bacteria in high-sugar (or other non-saline) media (Mycobacterium spp., Tetragenococcus halophilus, Saccharibacter floricola, Staphylococcus aureus and so on) and eukaryotic microbes in saline (Wallemia spp., Basipetospora halophila, Dunaliella spp. and so on) and high-sugar substrates (for example, Xeromyces bisporus, Zygosaccharomyces rouxii, Aspergillus and Eurotium spp.). We also manipulated the balance of chaotropic and kosmotropic stressors for the extreme, xerophilic fungi Aspergillus penicilloides and X. bisporus and, via this approach, their established water-activity limits for mycelial growth (∼0.65) were reduced to 0.640. Furthermore, extrapolations indicated theoretical limits of 0.632 and 0.636 a(w) for A. penicilloides and X. bisporus, respectively. Collectively, these findings suggest that there is a common water-activity limit that is determined by physicochemical constraints for the three domains of life.
authors.affiliation: Institute for Global Food Security, School of Biological Sciences, MBC, Queen's University Belfast, Belfast, Northern Ireland, UK.
authors.forename: Andrew
authors.initials: A
authors.lastname: Stevenson
authors.affiliation: Institute for Global Food Security, School of Biological Sciences, MBC, Queen's University Belfast, Belfast, Northern Ireland, UK.
authors.forename: Jonathan A
authors.initials: JA
authors.lastname: Cray
authors.affiliation: Institute for Global Food Security, School of Biological Sciences, MBC, Queen's University Belfast, Belfast, Northern Ireland, UK.
authors.forename: Jim P
authors.initials: JP
authors.lastname: Williams
authors.affiliation: 1] Institute for Global Food Security, School of Biological Sciences, MBC, Queen's University Belfast, Belfast, Northern Ireland, UK [2] Laboratório de Análises, Instituto Superior Técnico, Lisboa, Portugal.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Santos
authors.affiliation: University of Essex, School of Biological Sciences, Colchester, Essex, UK.
authors.forename: Richa
authors.initials: R
authors.lastname: Sahay
authors.affiliation: University of Essex, School of Biological Sciences, Colchester, Essex, UK.
authors.forename: Nils
authors.initials: N
authors.lastname: Neuenkirchen
authors.affiliation: Institute for Global Food Security, School of Biological Sciences, MBC, Queen's University Belfast, Belfast, Northern Ireland, UK.
authors.forename: Colin D
authors.initials: CD
authors.lastname: McClure
authors.affiliation: Institute for Global Food Security, School of Biological Sciences, MBC, Queen's University Belfast, Belfast, Northern Ireland, UK.
authors.forename: Irene R
authors.initials: IR
authors.lastname: Grant
authors.affiliation: Institute for Global Food Security, School of Biological Sciences, MBC, Queen's University Belfast, Belfast, Northern Ireland, UK.
authors.forename: Jonathan Dr
authors.initials: JD
authors.lastname: Houghton
authors.affiliation: Institute for Global Food Security, School of Biological Sciences, MBC, Queen's University Belfast, Belfast, Northern Ireland, UK.
authors.forename: John P
authors.initials: JP
authors.lastname: Quinn
authors.affiliation: Institute for Global Food Security, School of Biological Sciences, MBC, Queen's University Belfast, Belfast, Northern Ireland, UK.
authors.forename: David J
authors.initials: DJ
authors.lastname: Timson
authors.affiliation: School of Life Sciences, North Maharashtra University, Jalgaon, Maharashtra, India.
authors.forename: Satish V
authors.initials: SV
authors.lastname: Patil
authors.affiliation: Department of Food Engineering and Technology, Institute of Chemical Technology, Mumbai, India.
authors.forename: Rekha S
authors.initials: RS
authors.lastname: Singhal
authors.affiliation: Department of Physiology, Genetics and Microbiology, University of Alicante, Alicante, Spain.
authors.forename: Josefa
authors.initials: J
authors.lastname: Antón
authors.affiliation: CBS Fungal Biodiversity Centre, Utrecht, The Netherlands.
authors.forename: Jan
authors.initials: J
authors.lastname: Dijksterhuis
authors.affiliation: CSIRO Food and Nutrition, North Ryde, New South Wales, Australia.
authors.forename: Ailsa D
authors.initials: AD
authors.lastname: Hocking
authors.affiliation: Microbial Ecology and Biorational Control, Scientia Terrae Research Institute, Sint-Katelijne-Waver, Belgium.
authors.forename: Bart
authors.initials: B
authors.lastname: Lievens
authors.affiliation: Instituto de Pesquisa e Desenvolvimento, Universidade do Vale do Paraíba, São José dos Campos, São Paulo, Brazil.
authors.forename: Drauzio E N
authors.initials: DE
authors.lastname: Rangel
authors.affiliation: NASA Headquarters, Washington, DC, USA.
authors.forename: Mary A
authors.initials: MA
authors.lastname: Voytek
authors.affiliation: Department of Biology, Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia.
authors.forename: Nina
authors.initials: N
authors.lastname: Gunde-Cimerman
authors.affiliation: Hebrew University of Jerusalem, Department of Plant and Environmental Sciences, Alexander Silberman Institute of Life Sciences, Jerusalem, Israel.
authors.forename: Aharon
authors.initials: A
authors.lastname: Oren
authors.affiliation: 1] University of Essex, School of Biological Sciences, Colchester, Essex, UK [2] Institute of Microbiology, Technical University Braunschweig, Braunschweig, Germany.
authors.forename: Kenneth N
authors.initials: KN
authors.lastname: Timmis
authors.affiliation: University of Essex, School of Biological Sciences, Colchester, Essex, UK.
authors.forename: Terry J
authors.initials: TJ
authors.lastname: McGenity
authors.affiliation: 1] Institute for Global Food Security, School of Biological Sciences, MBC, Queen's University Belfast, Belfast, Northern Ireland, UK [2] University of Essex, School of Biological Sciences, Colchester, Essex, UK.
authors.forename: John E
authors.initials: JE
authors.lastname: Hallsworth
mesh_terms: D001105:Archaea / Q000378:metabolism; D016477:Artifacts; D001203:Ascomycota / Q000378:metabolism; D001230:Aspergillus / Q000378:metabolism*; D001419:Bacteria / Q000378:metabolism*; D002241:Carbohydrates / Q000737:chemistry; D005658:Fungi / Q000378:metabolism; D006217:Halobacterium / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D012965:Sodium Chloride / Q000737:chemistry; D013211:Staphylococcus aureus / Q000378:metabolism; D013696:Temperature; D014867:Water / Q000502:physiology; D014871:Water Microbiology
chemical_list: D002241:Carbohydrates; D014867:Water; D012965:Sodium Chloride