Nitrogen-fixing chemo-organotrophic bacteria isolated from cyanobacteria-deprived lichens and their ability to solubilize phosphate and to release amino acids and phytohormones

Abstract

Aims: Cyanobacteria‐deprived lichens of the species Canoparmelia caroliniana, Canoparmelia crozalsiana, Canoparmelia texana, Parmotrema sancti‐angeli and Parmotrema tinctorum were screened for the presence of chemo‐organotrophic nitrogen‐fixing bacteria. Methods and Results: Fifty‐three lichen samples subjected to enrichment selection using a nitrogen‐free minimal medium were positive for acetylene reduction. Seventeen isolates, able to fix nitrogen, belonged to Gamma‐proteobacteria group and were identified as: Acinetobacter sp., Pantoea sp., Pseudomonas sp., Pseudomonas stutzeri, Serratia marcescens and Stenotrophomonas maltophilia, according to 16S rRNA gene sequences and biochemical tests. The excretion of amino acid and phytohormone and the ability of mineral phosphate solubilization were determined in 14 isolates. All isolates were able to release amino acids and 3‐indoleacetic acid. About 64% of the isolates solubilized phosphates and 30% released ethylene. Conclusions: These data confirm sparse evidence from the literature on the occurrence of chemo‐organotrophic nitrogen‐fixing bacteria in cyanobacteria‐deprived lichens; the isolates presented physiologic features which might benefit the host if they are expressed when the bacteria are harboured by lichens. Significance and Impact of the Study: Chemo‐organotrophic nitrogen‐fixing bacteria were isolated from a high percentage (72·6%) of cyanobacteria‐deprived lichens. All isolates presented important physiological characteristics, some of which are being described here for the first time.

Molecular characterization of nitrogen-fixing bacteria isolated from brazilian agricultural plants at São Paulo state

“…1). In accordance with Liba et al, (2006), nitrogen fixation ability was a new character not previously reported for Stenotrophomonas, and only one publication refers to a Stenotrophomonas-like strain able to fix atmospheric nitrogen (Elo and Haahtela, 1999).…”

Bacterial Communities Associated with the Lichen Symbiosis

“…Lichen thalli host diverse populations of organisms, such as lichenicolous (growing on the thallus) (21) and endolichenic (growing within the thallus) fungal species (1). While nonphotosynthetic bacteria have long been suspected to be associated with lichens (32; but also see reference 8), modern culture-independent studies are just beginning to reveal the diversity in bacteria inhabiting lichens, suggesting that lichens host diverse assemblages from several bacterial phyla (7,8,14,16,17,23).The few studies that have characterized the bacterial communities of lichens by using molecular fingerprinting techniques are limited in their phylogenetic resolution and have yielded conflicting results. Grube et al (16) found that the community composition for certain lichen-associated bacterial groups (e.g., Alphaproteobacteria) exhibited species-specific patterns, and they advanced the idea that bacteria may be integral to the lichen symbiosis.…”

“…For example, there have been reports of bacterial nitrogenase reductase (nifH) genes (responsible for N 2 fixation) in bacteria isolated from lichens as well as within lichens themselves (16, 23). Bacteria found on internal and external surfaces of lichens may also help lichen symbionts to fulfill other nutritional requirements, including the acquisition of phosphorus and amino acids (16,23).Here we used bar-coded pyrosequencing with primers targeting the 16S rRNA gene to survey bacterial and archaeal diversity associated with surface-sterilized lichen thalli compared to that in nearby soils from a site in the western United States. Our objective was to determine if lichen-associated bacterial and archaeal communities are characteristic of lichen species, indicative of immediate spatial areas, or simply an extension of the surrounding soil environment.…”

Exploring functional contexts of symbiotic sustain within lichen-associated bacteria by comparative omics

“…With this new perspective in mind, we have now explored the potential functions of the bacterial communities with the goal of understanding their symbiotic context in a more holistic way. Functional analysis of the culturable fraction of the lichen-associated bacteria suggested their involvement in several roles, including iron and phosphate mobilization, hormone production, nitrogen fixation as well as several lytic activities (Liba et al, 2006;Grube et al, 2009). The culturable fraction usually represents only a minor part of the total lichenassociated microbiome and therefore most likely does not cover the host-dependent majority of the bacterial species (Cardinale et al, 2008).…”