title: Microbes at Surface-Air Interfaces: The Metabolic Harnessing of Relative Humidity, Surface Hygroscopicity, and Oligotrophy for Resilience.
abstract: The human environment is predominantly not aqueous, and microbes are ubiquitous at the surface-air interfaces with which we interact. Yet microbial studies at surface-air interfaces are largely survival-oriented, whilst microbial metabolism has overwhelmingly been investigated from the perspective of liquid saturation. This study explored microbial survival and metabolism under desiccation, particularly the influence of relative humidity (RH), surface hygroscopicity, and nutrient availability on the interchange between these two phenomena. The combination of a hygroscopic matrix (i.e., clay or 4,000 MW polyethylene glycol) and high RH resulted in persistent measurable microbial metabolism during desiccation. In contrast, no microbial metabolism was detected at (a) hygroscopic interfaces at low RH, and (b) less hygroscopic interfaces (i.e., sand and plastic/glass) at high or low RH. Cell survival was conversely inhibited at high RH and promoted at low RH, irrespective of surface hygroscopicity. Based on this demonstration of metabolic persistence and survival inhibition at high RH, it was proposed that biofilm metabolic rates might inversely influence whole-biofilm resilience, with 'resilience' defined in this study as a biofilm's capacity to recover from desiccation. The concept of whole-biofilm resilience being promoted by oligotrophy was supported in desiccation-tolerantArthrobacterspp. biofilms, but not in desiccation-sensitivePseudomonas aeruginosabiofilms. The ability of microbes to interact with surfaces to harness water vapor during desiccation was demonstrated, and potentially to harness oligotrophy (the most ubiquitous natural condition facing microbes) for adaptation to desiccation.
authors.affiliation: Department of Microbiology, University of Stellenbosch, Cape TownSouth Africa; Department of Chemistry and Biology, Ryerson University, Toronto, ONCanada.
authors.forename: Wendy
authors.initials: W
authors.lastname: Stone
authors.affiliation: Department of Microbiology, University of Stellenbosch, Cape TownSouth Africa; Department of Chemistry and Biology, Ryerson University, Toronto, ONCanada.
authors.forename: Otini
authors.initials: O
authors.lastname: Kroukamp
authors.affiliation: Department of Food and Bioproduct Sciences, University of Saskatchewan, Saskatoon, SK Canada.
authors.forename: Darren R
authors.initials: DR
authors.lastname: Korber
authors.affiliation: Environmental Geoscience, Nuclear Waste Management Organization, Toronto, ON Canada.
authors.forename: Jennifer
authors.initials: J
authors.lastname: McKelvie
authors.affiliation: Department of Microbiology, University of Stellenbosch, Cape TownSouth Africa; Department of Chemistry and Biology, Ryerson University, Toronto, ONCanada.
authors.forename: Gideon M
authors.initials: GM
authors.lastname: Wolfaardt
keywords: carbon; desiccation; metabolism; relative humidity; surface