AUTHOR=Cabrera-Rangel José Francisco , Mendoza-Servín Judit Valeria , Córdova-López Gonzalo , Alcalde-Vázquez Raúl , García-Estrada Raymundo Saúl , Winkler Robert , Partida-Martínez Laila P. 

TITLE=Symbiotic and toxinogenic Rhizopus spp. isolated from soils of different papaya producing regions in Mexico

JOURNAL=Frontiers in Fungal Biology

VOLUME=3

YEAR=2022

URL=https://www.frontiersin.org/journals/fungal-biology/articles/10.3389/ffunb.2022.893700

DOI=10.3389/ffunb.2022.893700

ISSN=2673-6128

ABSTRACT=<p>Mucoralean fungi from the genus <italic>Rhizopus</italic> are common inhabitants of terrestrial ecosystems, being some pathogens of animals and plants. In this study, we analyzed the symbiotic and toxinogenic potential of <italic>Rhizopus</italic> species derived from agricultural soils dedicated to the production of papaya (<italic>Carica papaya</italic> L.) in Mexico. Four representative strains of soil-derived <italic>Rhizopus</italic> spp. were analyzed employing molecular, microscopic, and metabolic methods. The ITS phylogenies identified the fungi as <italic>Rhizopus microsporus</italic> HP499, <italic>Rhizopus delemar</italic> HP475 and HP479, and <italic>Rhizopus homothallicus</italic> HP487. We discovered that <italic>R. microsporus</italic> HP499 and <italic>R. delemar</italic> HP475 harbor similar endofungal bacterial symbionts that belong to the genus <italic>Mycetohabitans</italic> (<italic>Burkholderia</italic> sensu lato) and that none of the four fungi were associated with <italic>Narnavirus</italic> RmNV-20S and RmNV-23S. Intriguingly, the interaction between <italic>R. delemar</italic> - <italic>Mycetohabitans</italic> showed different phenotypes from known <italic>R. microsporus</italic> - <italic>Mycetohabitans</italic> symbioses. Elimination of bacteria in <italic>R. delemar</italic> HP475 did not cause a detrimental effect on fungal growth or asexual reproduction. Moreover, metabolic and molecular analyses confirmed that, unlike symbiotic <italic>R. microsporus</italic> HP499, <italic>R. delemar</italic> HP475 does not produce rhizoxin, one of the best-characterized toxins produced by <italic>Mycetohabitans</italic> spp. The rhizoxin (<italic>rhi</italic>) biosynthetic gene cluster seems absent in this symbiotic bacterium. Our study highlights that the symbioses between <italic>Rhizopus</italic> and <italic>Mycetohabitans</italic> are more diverse than anticipated. Our findings contribute to expanding our understanding of the role bacterial symbionts have in the pathogenicity, biology and evolution of Mucorales.</p>