AUTHOR=Ali Md. Arshad , Lou Yang , Hafeez Rahila , Li Xuqing , Hossain Afsana , Xie Ting , Lin Li , Li Bin , Yin Yanni , Yan Jianli , An Qianli 

TITLE=Functional Analysis and Genome Mining Reveal High Potential of Biocontrol and Plant Growth Promotion in Nodule-Inhabiting Bacteria Within Paenibacillus polymyxa Complex

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.618601

DOI=10.3389/fmicb.2020.618601

ISSN=1664-302X

ABSTRACT=<p>Bacteria belonging to the genus <italic>Paenibacillus</italic> were frequently isolated from legume nodules. The nodule-inhabiting <italic>Paenibacillus</italic> as a resource of biocontrol and plant growth-promoting endophytes has rarely been explored. This study explored the nodule-inhabiting <italic>Paenibacillus</italic>’ antifungal activities and biocontrol potentials against broad-spectrum important phytopathogenic fungi. We collected strains which were isolated from nodules of <italic>Robinia pseudoacacia</italic>, <italic>Dendrolobium triangulare</italic>, <italic>Ormosia semicastrata</italic>, <italic>Cicer arietinum</italic>, <italic>Acacia crassicarpa</italic>, or <italic>Acacia implexa</italic> and belong to <italic>P. peoriae</italic>, <italic>P. kribbensis</italic>, <italic>P. endophyticus</italic>, <italic>P. enshidis</italic>, <italic>P. puldeungensis</italic>, <italic>P. taichungensis</italic>, or closely related to <italic>P. kribbensis</italic>, or <italic>P. anseongense</italic>. These nodule-inhabiting <italic>Paenibacillus</italic> showed diverse antagonistic activities against five phytopathogenic fungi (<italic>Fusarium graminearum</italic>, <italic>Magnaporthe oryzae</italic>, <italic>Rhizoctonia solani</italic>, <italic>Sclerotinia sclerotiorum</italic>, and <italic>Botrytis cinerea</italic>). Six strains within the <italic>P. polymyxa</italic> complex showed broad-spectrum and potent activities against all the five pathogens, and produced multiple hydrolytic enzymes, siderophores, and lipopeptide fusaricidins. Fusaricidins are likely the key antimicrobials responsible for the broad-spectrum antifungal activities. The nodule-inhabiting strains within the <italic>P. polymyxa</italic> complex were able to epiphytically and endophytically colonize the non-host wheat plants, produce indole acetic acids (IAA), and dissolve calcium phosphate and calcium phytate. <italic>P. peoriae</italic> strains RP20, RP51, and RP62 could fix N<sub>2</sub>. <italic>P. peoriae</italic> RP51 and <italic>Paenibacillus</italic> sp. RP31, which showed potent plant colonization and plant growth-promotion competence, effectively control fungal infection <italic>in planta</italic>. Genome mining revealed that all strains (<italic>n</italic> = 76) within the <italic>P. polymyxa</italic> complex contain <italic>ipdC</italic> gene encoding indole-3-pyruvate decarboxylase for biosynthesis of IAA, 96% (<italic>n</italic> = 73) contain the <italic>fus</italic> cluster for biosynthesis of fusaricidins, and 43% (<italic>n</italic> = 33) contain the <italic>nif</italic> cluster for nitrogen fixation. Together, our study highlights that endophytic strains within the <italic>P. polymyxa</italic> complex have a high probability to be effective biocontrol agents and biofertilizers and we propose an effective approach to screen strains within the <italic>P. polymyxa</italic> complex.</p>