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Lichen Substances Can Be The Carbon Nutrient Of Bacteriobionts

Posted on:2015-01-19Degree:MasterType:Thesis
Country:ChinaCandidate:Q XiaFull Text:PDF
GTID:2250330425996106Subject:Microbiology
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Despite living in a nutrition-poor condition, lichens often produce an astonishing amount ofsecondary compounds, even up to8%of the dry weight of lichen thallus. Although lichensubstances have been suggested to limit the damages of excessive sunlight, pathogenic microbes,or herbivores, it is still not enough to explain why the secondary compound content of lichenthallus is so high. Bacteriobionts are increasingly regarded as the integral components of lichenthalli, in addition to the photobionts and mycobionts. Rhizobiales and Alphaproteobacteria havebeen proved to be the predominant bacteriobionts. However, very few species of these groupswere isolated and cultured from lichens before. What dictates which bacteria could reside in thelichen thallus has not been definitely ascertained so far.Five specimens of Umbilicaria esculenta and five specimens of Parmelia omphalodes werecollected from Mt. Tulaopodingzi, Wangqing, Jilin, China. Five specimens of Lobaria retigerawere collected from Mt. Jiaozixueshan, Luquan, Yunnan, China. We first detect the cultivablebacteriobionts from Umbilicaria esculenta, Parmelia omphalodes and Lobaria retigera on thenitrogen-free media with corresponding lichen substances as the sole carbon source.A total of72isolates were obtained from5specimens of Umbilicaria esculenta.A total of93isolates wereobtained from5specimens of Parmelia omphalodes. A total of69isolates were obtained from5specimens of L. retigera. And easily obtain the predominant bacteriobionts of Rhizobiales andAlphaproteobacteria.This study first reveals that the most important role of lichen substances is providing carbonsource to bacteriobionts which complement the nitrogen budget of lichen thallus. Based on thisand previous studies, lichen substances are suggested to be the chief triggers of thelichen-associated bacterial community which constantly alters in certain range according to somerelated factors, such as photobiont-type, geography, age, sun, and substrate.A hypothesis about the cause of why most lichen substances are aromatic compounds isalso proposed.Lichens are one of the oldest land colonies. The aromatic compound, phenol, isone of the most abundant organic carbons on land before the colonization of land by lichens andplants. Therefore, the phenol-degrading bacteria with the nitrogen-fixing capability (PN bacteria) are possibly one of the predominant non-photosynthetic bacteria during this historical period. Innitrogen-poor condition, enriching the predominant PN bacteria to complement the nitrogenbudget will present great advantage of natural selection to chlorolichens. This may evolutionarilyresult in most lichens producing abundant aromatic compounds.First describes the symbiotic pattern of bacteriobionts.The mycobiont and photobiont forman obligate symbiosis. However, our study shows many species of bacteriobionts are containedin a lichen thallus, and almost all of them can be found in other environments in addition tolichen thalli.These results show that the bacteriobionts do not form an obligate symbiosis withthe mycobionts and photobionts. The bacteriobionts may repeatedly die and colonize during thelong life time of lichens, since there are abundant free-living bacteriobionts in nature. Thosedead bacteriobionts could become the nutrient source, especially nitrogen source of themycobionts, photobionts and other microbes associated with lichens. This symbiotic patternwould result in geography becoming a factor affecting the bacterial communities in lichen thalli,since the bacteriobionts are constantly updating from the local environment. This symbioticpattern would also result in more uniform bacterial community in the growing parts of lichenthallus than that in the ageing parts, since the growing parts are constantly inhabited by the newcolonies of bacteriobionts, whereas the ageing parts contain more dead bacteriobionts (namely,more abundant nutrition) and then allow more various bacteria even including non-bacteriobiontsto colonize here.
Keywords/Search Tags:bacteriobionts, lichen substances, symbiosis, nitrogen fixation, phenol degradation, aromatic compounds, isolation, culture, Alphaproteobacteria, Rhizobiales, LAR1, Actinobacteria
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