These observations highlight a bias toward liquid systems that has pervaded microbiological research for decades.
Similarly, Brown articulated that, since prokaryotes predominantly obtain nutrients from solution, even a desiccated environment is essentially just a “concentrated solution with which the microbial cell must come directly to thermodynamic terms” in order to persist ( Brown, 1976). In the microbial context, one of the earlier fundamental reviews on water activity in soil underscored this by calling single-cellular microbes aquatic creatures, regardless of their habitat ( Stotzky and Pramer, 1972). Water is widely considered the determining element of the metabolic network that constitutes life on earth ( Zolensky, 2005). 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.
biofilms, but not in desiccation-sensitive Pseudomonas aeruginosa biofilms. The concept of whole-biofilm resilience being promoted by oligotrophy was supported in desiccation-tolerant Arthrobacter spp. 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. Cell survival was conversely inhibited at high RH and promoted at low RH, irrespective of surface hygroscopicity. 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. 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. 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. Yet microbial studies at surface-air interfaces are largely survival-oriented, whilst microbial metabolism has overwhelmingly been investigated from the perspective of liquid saturation. The human environment is predominantly not aqueous, and microbes are ubiquitous at the surface-air interfaces with which we interact.