The genus Micromonospora is widespread in legume root nodules: the example of Lupinus angustifolius

Abstract

Our current knowledge of plant-microbe interactions indicate that populations inhabiting a host plant are not restricted to a single microbial species but comprise several genera and species. No one knows if communities inside plants interact, and it has been speculated that beneficial effects are the result of their combined activities. During an ecological study of nitrogen-fixing bacterial communities from Lupinus angustifolius collected in Spain, significant numbers of orangepigmented actinomycete colonies were isolated from surface-sterilized root nodules. The isolates were analysed by BOX-PCR fingerprinting revealing an unexpectedly high genetic variation. Selected strains were chosen for 16S rRNA gene sequencing and phylogenetic analyses confirmed that all strains isolated belonged to the genus Micromonospora and that some of them may represent new species. To determine the possibility that the isolates fixed atmospheric nitrogen, chosen strains were grown in nitrogen-free media, obtaining in some cases, significant growth when compared with the controls. These strains were further screened for the presence of the nifH gene encoding dinitrogenase reductase, a key enzyme in nitrogen fixation. The partial nifH-like gene sequences obtained showed a 99% similarity with the sequence of the nifH gene from Frankia alni ACN14a, an actinobacterium that induces nodulation and fixes nitrogen in symbiosis with Alnus. In addition, in situ hybridization was performed to determine if these microorganisms inhabit the inside of the nodules. This study strongly suggests that Micromonospora populations are natural inhabitants of nitrogen-fixing root nodules.

Taxonomy, Physiology, and Natural Products of Actinobacteria

“…However, molecular studies have increased the number of known nifH-containing Actinobacteria beyond Frankia spp. (587)(588)(589)(590)(591). The discovery of these actinobaceria has stimulated further discussion and inquiries on the origin and emergence of diazotrophy among Actinobacteria.…”

“…constitute protective mutualistic symbioses in which the host feeds and protects the bacteria and in return the bacteria provide antibiotics to protect the host, or their resources, from pathogens (585). Other genera of Actinobacteria, namely, Frankia and Micromonospora, form mutualistic symbioses with higher organisms via nitrogenfixing actinonodules in trees and shrubs (586,587).…”

Micromonospora cremea sp. nov. and Micromonospora zamorensis sp. nov., isolated from the rhizosphere of Pisum sativum

“…Recent reports on the isolation of novel members of the genus Micromonospora from diverse habitats (de Menezes et al, 2008;Kirby & Meyers, 2010;Maldonado et al, 2008;Thawai et al, 2005Thawai et al, , 2007Tanasupawat et al, 2010;Trujillo et al, 2010;Wang et al, 2011) indicate the ability of these micro-organisms to adapt to very different niches, highlighting their metabolic diversity. The genus Micromonospora has moved from a 'forgotten-status' with 14 species described in 2000 (Kasai et al, 2000) to 43 at the present time (Euzéby, 2011).…”

Paenibacillus lupini sp. nov., isolated from nodules of Lupinus albus

“…Lupinus albus is one of the most cultivated Lupinus species (Wolko et al, 2011) establishing nitrogen-fixing symbiosis with Bradyrhizobium canariense and Bradyrhizobium japonicum in Spain (Velázquez et al, 2010) that can be joined by other endophytes in Lupinus nodules (Ardley et al, 2012;Trujillo et al, 2007Trujillo et al, , 2010Flores-Félix et al, 2014). Currently there is an increasing interest in the diversity study of legume nodule endophytes since some data suggested that the nodule microbiome has a complex structure comprising several plant growth promoters which have great interest in the future design of biofertilizers (Velázquez et al, 2013).…”