Adaptive Strategies in a Poly-Extreme Environment: Differentiation of Vegetative Cells in Serratia ureilytica and Resistance to Extreme Conditions

Abstract

Poly-extreme terrestrial habitats are often used as analogs to extra-terrestrial environments. Understanding the adaptive strategies allowing bacteria to thrive and survive under these conditions could help in our quest for extra-terrestrial planets suitable for life and understanding how life evolved in the harsh early earth conditions. A prime example of such a survival strategy is the modification of vegetative cells into resistant resting structures. These differentiated cells are often observed in response to harsh environmental conditions. The environmental strain (strain Lr5/4) belonging to Serratia ureilytica was isolated from a geothermal spring in Lirima, Atacama Desert, Chile. The Atacama Desert is the driest habitat on Earth and furthermore, due to its high altitude, it is exposed to an increased amount of UV radiation. The geothermal spring from which the strain was isolated is oligotrophic and the temperature of 54°C exceeds mesophilic conditions (15 to 45°C). Although the vegetative cells were tolerant to various environmental insults (desiccation, extreme pH, glycerol), a modified cell type was formed in response to nutrient deprivation, UV radiation and thermal shock. Scanning (SEM) and Transmission Electron Microscopy (TEM) analyses of vegetative cells and the modified cell structures were performed. In SEM, a change toward a circular shape with reduced size was observed. These circular cells possessed what appears as extra coating layers under TEM. The resistance of the modified cells was also investigated, they were resistant to wet heat, UV radiation and desiccation, while vegetative cells did not withstand any of those conditions. A phylogenomic analysis was undertaken to investigate the presence of known genes involved in dormancy in other bacterial clades. Genes related to spore-formation in Myxococcus and Firmicutes were found in S. ureilytica Lr5/4 genome; however, these genes were not enough for a full sporulation pathway that resembles either group. Although, the molecular pathway of cell differentiation in S. ureilytica Lr5/4 is not fully defined, the identified genes may contribute to the modified phenotype in the Serratia genus. Here, we show that a modified cell structure can occur as a response to extremity in a species that was previously not known to deploy this strategy. This strategy may be widely spread in bacteria, but only expressed under poly-extreme environmental conditions.

Insights Into the Microbiology of the Chaotropic Brines of Salar de Atacama, Chile

“…In conclusion, we report the isolation of two bacterial species from one of the most hypersaline environments described to date on Earth (total salinity = 556 g/L), where lithium chloride is the principal salt. Furthermore, we established the bacteriostatic effects of lithium on the microbial cells and we suggest that the NaCl-tolerance, generation of spores and fluidity change of membrane of Bacillus could be keys to survive in this poly-extreme environment, as reported elsewhere (Filippidou et al, 2019). The information detailed here is likely relevant to the search for microbial life in planets and other celestial bodies with surficial salt-lakes or brines that provide a potential niche for microbial life.…”

The biological prospective of red-pigmented bacteria cultured from contaminated agar media

“…Serratia marcescens AL2-16 that associated with Achyranthes aspera L was reported to enhance plant growth-promoting properties (Devi et al 2016). Serratia ureilytica species were found from extreme environmental habitats (Filippidou et al 2019). Drosophila melanogaster had known to be a source of microbial association host, Serratia was included (Chambers et al 2019;Gilbert et al 2020).…”

Characterization and identification of three thermophilic Bacillus strain isolated from Domas Crater, Mt. Tangkuban Perahu, Indonesia

“…Liu et al (2017) have isolated B. paramycoides from four coordinates in India and one Coordinate in Indonesia. According to Filippidou et al (2019), cell structure can change in response to previously unknown species applying a self-protection strategy and only expressed in extreme environmental conditions.…”