Antimicrobial Secondary Metabolites Of Three Lichen-associated Actinomycetes

Antibiotics produced by microorganisms have made an indelible contribution to human health,Among them,actinomycetes are important sources for the discovery of drug lead compounds.However,with the long-term development and utilization of actinomycetes drug resources,especially the isolation of a large number of repeat strains and known compounds from soil actinomycetes,discovering new bioactive compounds becomes more and more difficult.Lichen-associated actinomycetes are the new resources to find new bioactive compounds from microorganism.Lichen is a kind of unique biological group,which is the symbiosis formed by symbiotic bacteria and symbiotic algae or cyanobacteria.At present,there are only few studies on the resources of actinomycetes from lichen,and few reports on the secondary metabolites of lichen-associated actinomycetes.This paper carried out the relative research,and tried to find bioactive compounds from actinomycetes derived from lichen.Fifteen lichen-associated actinomycete strains were screened for their chemical diversity of fermentation products and antimicrobial activity.Three strains,including Amycolatopsis sp.YIM130687,Streptomyces sp.YIM130896,and Streptomyces sp.YIM130932 were selected for further chemical study.A total of 22 compounds were isolated and characterized from three strains using various methods of isolation and spectroscopic analyses.Six compounds were isolated and characterized from the strain YIM130932.They were 7-O-methylkoninginin D(1),koninginin E(2),cyclo-(Gly-Phe)(3),cyclo-(Phe-Tyr)(4),cyclo-(Leu-Tyr)(5),cyclo-(Ala-Leu)(6).Two polyketides were isolated and characterized from the cluture broth of the strain YIM130896.They were identified as resistomysin(7)and tetracenomycin D(8).Fourteen natural compounds were isolated and characterized from the YIM 130687.They were indentified as 4-(3-methylbut-2-enyloxy)benzamide(9),2-carbamoyl-3-hydroxy-1,4-naphthoquinone.(10),manalin(11),1-pyrrole-2-carboxamide.(12),cyclo-(Gly-Ala)(13),cyclo(L-Pro-L-Leu)(14),benzeneacetamide(15),tumagainolide B(16),uracil(17),2-hydroxy-3-methyl-4-pyrone(18),anthranilic acid(19),genistein(20),prunetin(21),(3S)-3-methyl-2,6-piperazinedione(22).The two koninginins(1 and 2)were isolated from actinomycetes,which were obtained previously only from fungi.Compounds 9,10,18 were previously obtained only from higher plants,and firstly discovered from microbial sources in this paper.Biological activity test showed that compound 7 obviously inhibited MRSA,S.aureus,S.typhimurium,C.albicans,F.graminearum and B.cinerea with MIC values in the range of 1-2 ?g/ml.Compound 10 significant inhibited three bacterial pathogens(MRSA,S.aureus,S.typhimurium)and the growth of three fungal pathogens(C.albicans,F.graminearum,B.cinerea)with MIC values of 2,2,16,32,1,1 ?g/ml,respectively.The results showed that lichen-associated actinomycetes could produce various types of secondary metabolites.Three compounds were isolated from microorganism for the first time,which could provide a new natural source for obtaining these compounds.The study also proved that actinomycetes could produce koninginins,which were only found in fungi before.