Abstract
Halophilic and halotolerant microorganisms represent promising sources of salt-tolerant enzymes that could be used in various biotechnological processes where high salt concentrations would otherwise inhibit enzymatic transformations. Considering the current need for more efficient biocatalysts, the present study aimed to explore the microbial diversity of five under- or uninvestigated salty lakes in Romania for novel sources of hydrolytic enzymes. Bacteria, archaea and fungi were obtained by culture-based approaches and screened for the production of six hydrolases (protease, lipase, amylase, cellulase, xylanase and pectinase) using agar plate-based assays. Moreover, the phylogeny of bacterial and archaeal isolates was studied through molecular methods. From a total of 244 microbial isolates, 182 (74.6%) were represented by bacteria, 22 (9%) by archaea, and 40 (16.4%) by fungi. While most bacteria synthesized protease and lipase, the most frequent hydrolase produced by fungi was pectinase. The archaeal isolates had limited hydrolytic activity, being able to produce only amylase and cellulase. Among the taxonomically identified isolates, the best hydrolytic activities were observed in halotolerant bacteria belonging to the genus Bacillus and in extremely halophilic archaea of the genera Haloterrigena and Halostagnicola. Therefore, the present study highlights that the investigated lakes harbor various promising species of microorganisms able to produce industrially valuable enzymes.
Highlights
Halophiles are a heterogeneous group of extremophilic organisms able to survive and even thrive in highly saline environments, unfavorable for the existence of most life forms known to us [1]
Salt-tolerant enzymes produced by halophilic and halotolerant microorganisms have been proposed as more efficient alternatives to mesophilic counterparts for catalyzing various industrial reactions carried out under high salinity conditions [8,9,10]
Some halophilic hydrolases such as amylase, cellulase, xylanase and lipase may be used for the breakdown of different kinds of non-food biomasses and the production of biofuels [16]
Summary
Halophiles are a heterogeneous group of extremophilic organisms able to survive and even thrive in highly saline environments, unfavorable for the existence of most life forms known to us [1]. They can be found in all three domains of life (i.e., Bacteria, Archaea and Eukarya) and are typically categorized on the basis of their salt requirement and tolerance. Halophilic (growing best at 0.5–2.5 M NaCl) and halotolerant bacteria (growing in the absence as well as in the presence of relatively high salt concentrations) are spread over a large number of phylogenetic branches, most species being grouped in the Proteobacteria (Gamma- and Alphaproteobacteria), Firmicutes and Actinobacteria [4]. Within the domain Eukarya, halophily is less widespread, the best salt-adapted eukaryotes being represented by few species of green algae (e.g., Dunaliella), yeasts (e.g., Hortaea werneckii), filamentous fungi (e.g., Wallemia ichthyophaga) and protozoa (e.g., Halocafeteria seosinensis) [5]
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