The Ecophysiological Performance and Traits of Genera within the Stichococcus-like Clade (Trebouxiophyceae) under Matric and Osmotic Stress.

Anh Tu Van,Karin Glaser,Veronika Sommer

doi:10.3390/microorganisms9091816

Abstract

Changes in water balance are some of the most critical challenges that aeroterrestrial algae face. They have a wide variety of mechanisms to protect against osmotic stress, including, but not limited to, downregulating photosynthesis, the production of compatible solutes, spore and akinete formation, biofilms, as well as triggering structural cellular changes. In comparison, algae living in saline environments must cope with ionic stress, which has similar effects on the physiology as desiccation in addition to sodium and chloride ion toxicity. These environmental challenges define ecological niches for both specialist and generalist algae. One alga known to be aeroterrestrial and euryhaline is Stichococcus bacillaris Nägeli, possessing the ability to withstand both matric and osmotic stresses, which may contribute to wide distribution worldwide. Following taxonomic revision of Stichococcus into seven lineages, we here examined their physiological responses to osmotic and matric stress through a salt growth challenge and desiccation experiment. The results demonstrate that innate compatible solute production capacity under salt stress and desiccation tolerance are independent of one another, and that salt tolerance is more variable than desiccation tolerance in the Stichococcus-like genera. Furthermore, algae within this group likely occupy similar ecological niches, with the exception of Pseudostichococcus.

Highlights

Terrestrial algae, abundant in both extreme and temperate environments, are exposed to several abiotic stressors related to their habitat outside the aquatic environment such as UV radiation, freezing, and unpredictable water availability, where periods of drought of several weeks or even months punctuated by rains are common [1,2,3]
There was a difference in how the biomass was distributed. Certain strains, such as Deuterostichococcus tetrallantoideus ASIB-IB-37 (Figure 3C), showed homogenous biomass, whereas others formed a condensed clump under salinity stress (Figure 3A,D)
The patterns observed in the growth experiments under salinity stress, osmolyte analysis, and desiccation stress experiment indicate that the Stichococcus-like strains are euryhaline but better adapted to dehydration than osmotic stress

Summary

Introduction

Terrestrial algae, abundant in both extreme and temperate environments, are exposed to several abiotic stressors related to their habitat outside the aquatic environment such as UV radiation, freezing, and unpredictable water availability, where periods of drought of several weeks or even months punctuated by rains are common [1,2,3]. Matric stress on algae is caused unequal water attraction potentials (Ψm ) between the cell and environment [11]. Osmotic stress in the form of salt in the surrounding environment may be significant, e.g., in marine environments. While dry conditions reduce the amount of water available from the environment, osmotic stress disrupts the normal cellular ion concentrations; Na+ and Cl− ions are toxic in high concentrations [13]

Objectives

Methods

Results

Discussion

Conclusion