Aspergillus penicillioides differentiation and cell division at 0.585 water activity

Abstract

SummaryWater availability acts as the most stringent constraint for life on Earth. Thus, understanding the water relations of microbial extremophiles is imperative to our ability to increase agricultural productivity (e.g., by enhancing the processing and turnover of dead organic matter in soils of arid regions), reduce human exposure to mycotoxins in buildings and our foodsupply chain, prevent the spoilage of foods/animal feeds, books, museum specimens and artworks and better control microbiology of industrial fermentations. Only a small number of microbial systems can retain activity at <0.710 water activity (ISME J 2015 9: 1333-1351). It has long-been considered that the most resilient of these is Xeromyces bisporus, which inhabits sugar-rich substrates (Appl Environ Microbiol 1968 16: 1853-1858. The current study focused on germination of Aspergillus penicillioides, a xerophile which is also able to grow under low humidity and saline conditions. Investigations of germination differed from those reported earlier: firstly, aerially borne conidia were harvested, and then used for inoculations, in their dry condition; secondly, cultures were incubated at 248C, i.e. below optimum germination temperature, to minimize the possibility of water loss from the substrate; thirdly, cultures remained sealed throughout the 73-day study period (microscopic examination was carried out directly 48 through the Petri plate lid); fourthly, the germination parameters determined were: rates and extent of conidial swelling, production of differentiated germinationstructures and septate germlings, and subsequent development of mycelium and/or sporulation; fifthly, assessments were carried out over a range of wateractivity values and time points to obtain a complete profile of the germination process. Conidia swelled, formed differentiated germination-structures and then produced septate germlings at a water-activity of just 0.585 (58.5% relative humidity), outside the currently understood thermodynamic window for life. Furthermore, analyses of these data suggest a theoretical water-activity minimum of 0.565 for germination of A. penicilliodes. In relation to astrobiology, these findings have an application in understanding the limits to life in extraterrestrial environments. In light of current plans for exploration missions to Mars and other places, and the need to safeguard martian scientific sites and potential resources (including water) for future human habitation, a knowledge-based and effective policy for planetary protection is essential. As it is, Mars-bound spacecraft may frequently be contaminated with aspergilli (including A. penicillioides) and other organisms which, when transported to other planetary bodies, pose a contamination risk. In crafting countermeasures to offset this, it is important to know as precisely as possible the capabilities of these potential interplanetary visitors.

Prokaryotic diversity and community composition in the Salar de Uyuni, a large scale, chaotropic salt flat

“…Similar results, although not explicitly mentioned, were found in Tunisian magnesiumrich bittern brines (around 3.9 M Mg 21 ) (Baati et al, 2011). Members of some bacterial and archaeal classes identified at SdU are similar to those detected in deep hypersaline anoxic basins, which contain MgCl 2 concentrations up to 5M (van der Wielen et al, 2005). For instance, Halorhabdus, which had never been reported previously in SdU, constituted 33% of the clone libraries from the deep hypersaline anoxic basins (van der Wielen et al, 2005).…”

“…Members of some bacterial and archaeal classes identified at SdU are similar to those detected in deep hypersaline anoxic basins, which contain MgCl 2 concentrations up to 5M (van der Wielen et al, 2005). For instance, Halorhabdus, which had never been reported previously in SdU, constituted 33% of the clone libraries from the deep hypersaline anoxic basins (van der Wielen et al, 2005). The persistence and presence of those phylums in chaotropic zones of SdU suggests that those microorganisms could be classified in the future as chaotolerant (Williams and Hallsworth, 2009), however, further culture-based studies are needed to further clarify this point.…”

Analysis of microbial communities in natural halite springs reveals a domain‐dependent relationship of species diversity to osmotic stress

“…Only a weak correlation between species diversity and salinity was detected for the microbial eukaryotes. We suggest two separate explanations for this trend: first, eukaryotes primarily use glycerol as an osmotic solute (Oren, ; Stevenson et al ., ) and, second, most of the eukaryotes present are oxygenic phototrophs. Glycerol is among the least energetically expensive solutes to synthesize, requiring only 30 ATP per molecule.…”

2038 – When microbes rule the Earth

“…For all of the foregoing reasons it is important to determine the windows of life, the boundaries of which are continuously being stretched. For example, the water activity limit for growth of 0.605 has been reduced to 0.585 in the fungus Aspergillus penicillioides (Stevenson et al, 2016). While, Planococcus halocryophilus, isolated from high Arctic permafrost, divides at −15 C and remains metabolically active at −25 C (Mykytczuk et al, 2013).…”