Abstract
The diversity of lichen-associated bacteria from lichen taxa Cetraria, Cladonia, Megaspora, Pseudephebe, Psoroma, and Sphaerophorus was investigated by sequencing of 16S rRNA gene amplicons. Physiological characteristics of the cultured bacterial isolates were investigated to understand possible roles in the lichen ecosystem. Proteobacteria (with a relative abundance of 69.7–96.7%) were mostly represented by the order Rhodospirillales. The 117 retrieved isolates were grouped into 35 phylotypes of the phyla Actinobacteria (27), Bacteroidetes (6), Deinococcus-Thermus (1), and Proteobacteria (Alphaproteobacteria (53), Betaproteobacteria (18), and Gammaproteobacteria (12)). Hydrolysis of macromolecules such as skim milk, polymer, and (hypo)xanthine, solubilization of inorganic phosphate, production of phytohormone indole-3-acetic acid, and fixation of atmospheric nitrogen were observed in different taxa. The potential phototrophy of the strains of the genus Polymorphobacter which were cultivated from a lichen for the first time was revealed by the presence of genes involved in photosynthesis. Altogether, the physiological characteristics of diverse bacterial taxa from Antarctic lichens are considered to imply significant roles of lichen-associated bacteria to allow lichens to be tolerant or competitive in the harsh Antarctic environment.
Highlights
Lichens form symbiotic relationships between fungi and photosynthetic algae and/or cyanobacteria [1,2,3]
Despite the general definition of lichens as bipartite or tripartite according to the mycobiont and photobiont symbioses, the presence of other microorganisms such as lichenassociated fungi, microalgae, and bacteria in the lichen thalli as an additional and integral component of lichen has long been revealed [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]
The aim of this study was to obtain bacterial isolates belonging to Alphaproteobacteria, the dominant lineage from six Antarctic lichen genera, Cetraria, Cladonia, Megaspora, Pseudephebe, Psoroma, and Sphaerophorus
Summary
Lichens form symbiotic relationships between fungi (mycobiont) and photosynthetic algae and/or cyanobacteria (photobiont) [1,2,3]. Lichens are usually highly tolerant to harsh environmental conditions such as extremes in temperature, low water content, low nutrient availability, and high ultraviolet light intensities. Several putative functional roles of bacteria such as nitrogen fixation, phosphate solubilization, amino acids and phytohormones production, nutrient supply via hydrolysis of major organic compounds, and defense mechanisms through antagonistic activities within the lichen symbiosis have been suggested, and these functions are considered to help lichens survive
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