Desiccation as a Long-Term Survival Mechanism for the Archaeon Methanosarcina barkeri

Abstract

Viable methanogens have been detected in dry, aerobic environments such as dry reservoir sediment, dry rice paddies and aerobic desert soils, which suggests that methanogens have mechanisms for long-term survival in a desiccated state. In this study, we quantified the survival rates of the methanogenic archaeon Methanosarcina barkeri after desiccation under conditions equivalent to the driest environments on Earth and subsequent exposure to different stress factors. There was no significant loss of viability after desiccation for 28 days for cells grown with either hydrogen or the methylotrophic substrates, but recovery was affected by growth phase, with cells desiccated during the stationary phase of growth having a higher rate of recovery after desiccation. Synthesis of methanosarcinal extracellular polysaccharide (EPS) significantly increased the viability of desiccated cells under both anaerobic and aerobic conditions compared with that of non-EPS-synthesizing cells. Desiccated M. barkeri exposed to air at room temperature did not lose significant viability after 28 days, and exposure of M. barkeri to air after desiccation appeared to improve the recovery of viable cells compared with that of desiccated cells that were never exposed to air. Desiccated M. barkeri was more resistant to higher temperatures, and although resistance to oxidative conditions such as ozone and ionizing radiation was not as robust as in other desiccation-resistant microorganisms, the protection mechanisms are likely adequate to maintain cell viability during periodic exposure events. The results of this study demonstrate that after desiccation M. barkeri has the innate capability to survive extended periods of exposure to air and lethal temperatures.A s more microorganisms are discovered in extreme environments on Earth that were previously considered to be devoid of life, we have been redefining the physical and chemical parameters for life to exist. One such extreme is the long-term storage of viable cells in a desiccated state, which imposes physiological constraints that many species cannot tolerate. A common characteristic of known desiccation-tolerant microorganisms, which include spore-forming bacteria, heterocyst-forming cyanobacteria, heteropolysaccharide-forming Beijerinckia, and Deinococcus, is the formation of relatively thick outer cell layers (32). The synthesis of an outer cell layer often composed of an extracellular polysaccharide (EPS), in conjunction with other mechanisms such as robust DNA repair and compatible solute formation, enables the cells to retain the minimal intracellular water activity required for survival (32).The methanogenic Archaea, despite their preference for highly reduced, anoxic conditions in order to grow, are globally distributed in a wide range of anaerobic, aquatic environments, including Antarctic lakes, submarine hydrothermal vents, rice paddies, sewage digestors, and as symbionts in rumen, termites, protozoa, and human large intestines (38). Among the least anticipated environments wher...

Microbial Diversity in Soil, Sand Dune and Rock Substrates of the Thar Monsoon Desert, India

“…Similarly the Chloroflexi and alpha proetobacterial phylotypes affiliated with common desert taxa [31,42] and those from other extreme environments [43]. Whilst the archaea comprised a very small part of the overall community, phylotypes indicated desert-adapted taxa such as Methanosarcina, a stresstolerant methanogenic archaeaon known for survival of desiccation stress [36].…”

“…These include cyanobacteria belonging to the genera, Pseudanabaenaceae, Chroococcidiopsis, Phromidium, Microcoleus [13,25,[31][32][33]; heterotrophic bacterial phylotypes belonging to the genera Rubrobacter, Arthrobacter, Sphingomonas, Chloroflexus, Roseiflexus, Pontibacter [9,34], fungal phylotypes belonging to, Mattirolomyces, Ascobolus, Chaetomium, Preussia, Chaetothyriales, Rhodotorula [7,35]; and archaeal phylotypes belonging to Methanosarcina and Thermotoplasmata [36]. The key finding that fungi dominate sand dunes whereas bacteria dominate soils is of interest.…”

Plant Desiccation Tolerance and its Regulation in the Foliage of Resurrection “Flowering-Plant” Species

“…It is thought that chloroplasts are derived from cyanobacteria [24], mitochondria from bacteria, and that the eukaryote nucleus has origins in the early archaea, with some inflow from bacteria [25,26]. Each of these endosymbionts may have contributed via the derivative organelles to the desiccation tolerance of plants, since desiccation-tolerant species occur in extant archaea (e.g., Methanosarcina barkeri, [27]), bacteria [28,29] and cyanobacteria (see [10]). …”

Microbial Anaerobic Digestion (Bio-Digesters) as an Approach to the Decontamination of Animal Wastes in Pollution Control and the Generation of Renewable Energy

“…[44] also noted that after dessication process, M. barkeri had innate capability to survive extended periods of exposure to air and lethal temperatures owing to the synthesis of thick outer cell layers composed of extracellular polysaccharide (EPS); added to the accumulation of cyclic 2,3-diphosphoglycerate (a novel metabolite which may be used to stabilize proteins at elevated temperatures). In addition, the membrane lipids of archael species have glycerol molecules bound by ether linkages to branched isoprene hydrocarbon molecules causing the organisms to adjust to such extreme temperatures [45].…”