Cultivation of halophilic archaea (class Halobacteria) from thalassohaline and athalassohaline environments

Abstract

As a group, the halophilic archaea (class Halobacteria) are the most salt-requiring and salt-resistant microorganisms within the domain Archaea. Halophilic archaea flourish in thalassohaline and athalassohaline environments and require over 100-150 g/L NaCl for growth and structural stability. Natural hypersaline environments vary in salt concentration, chemical composition and pH, and occur in climates ranging from tropical to polar and even under-sea. Accordingly, their resident haloarchaeal species vary enormously, as do their individual population compositions and community structures. These diverse halophilic archaeal strains are precious resources for theoretical and applied research but assessing their taxonomic and metabolic novelty and diversity in natural environments has been technically difficult up until recently. Environmental DNA-based high-throughput sequencing technology has now matured sufficiently to allow inexpensive recovery of massive amounts of sequence data, revealing the distribution and community composition of halophilic archaea in different hypersaline environments. While cultivation of haloarchaea is slow and tedious, and only recovers a fraction of the natural diversity, it is the conventional means of describing new species, and provides strains for detailed study. As of the end of May 2020, the class Halobacteria contains 71 genera and 275 species, 49.8% of which were first isolated from the marine salt environment and 50.2% from the inland salt environment, indicating that both thalassohaline and athalassohaline environments contain diverse halophilic archaea. However, there remain taxa that have not yet been isolated in pure culture, such as the nanohaloarchaea, which are widespread in the salt environment and may be one of the hot spots in the field of halophilic archaea research in the future. In this review, we focus on the cultivation strategies that have been used to isolate extremely halophilic archaea and point out some of the pitfalls and challenges.

Natrinema halophilum sp. nov., Natrinema salinisoli sp. nov., Natrinema amylolyticum sp. nov. and Haloterrigena alkaliphila sp. nov., four extremely halophilic archaea isolated from salt mine, saline soil and salt lake

“…Halophilic archaea typically inhabit hypersaline environments such as salt lakes, solar salterns, salt mines and saline soils [1]. Diverse halophilic archaea of the genera Natrinema and Haloterrigena could be isolated from diverse hypersaline environments.…”

Mining of the biosynthetic potential of archaea reveals diverse anti-archaeal lanthipeptides

“…Being the products of haloarchaea isolated from halophilic environments predominated by archaea 42 , archalan α exhibited narrow-spectrum anti-archaeal against phylogenetically-related halophilic archaea (Supplementary Table 6). These results suggested that archalan may play a role in antagonistic interaction of the halophilic niche.…”

Halobaculum rubrum sp. nov., an extremely halophilic archaeon isolated from a salt lake

“…A series of tenfold dilutions were made by using the NHM liquid medium. Purified agar powder (Sinopharm Chemical Rengent; 1.5 %, w/v) was added to prepare the NHM agar plates [8]. Two hundred microlitres of each tenfold dilution was spread onto NHM agar plates and incubated at 37 °C for 1 month.…”