Monitoring the colonization and infection of legume nodules by Micromonospora in co-inoculation experiments with rhizobia.

The discovery that the actinobacterium Micromonospora inhabits nitrogen-fixing nodules raised questions as to its potential ecological role. The capacity of two Micromonospora strains to infect legumes other than their original host, Lupinus angustifolius, was investigated using Medicago and Trifolium as test plants. Compatible rhizobial strains were used for coinoculation of the plants because Micromonospora itself does not induce nodulation. Over 50% of nodules from each legume housed Micromonospora, and using 16S rRNA gene sequence identification, we verified that the reisolated strains corresponded to the microorganisms inoculated. Entry of the bacteria and colonization of the plant hosts were monitored using a GFP-tagged Lupac 08 mutant together with rhizobia, and by using immunogold labeling. Strain Lupac 08 was localized in plant tissues, confirming its capacity to enter and colonize all hosts. Based on studying three different plants, our results support a non-specific relationship between Micromonospora and legumes. Micromonospora Lupac 08, originally isolated from Lupinus re-enters root tissue, but only when coinoculated with the corresponding rhizobia. The ability of Micromonospora to infect and colonize different legume species and function as a potential plant-growth promoting bacterium is relevant because this microbe enhances the symbiosis without interfering with the host and its nodulating and nitrogen-fixing microbes.

Genome sequence of Micromonospora lupini Lupac 08, isolated from root nodules of Lupinus angustifolius.

Micromonospora strains have been isolated from diverse niches, including soil, water, and marine sediments and root nodules of diverse symbiotic plants. In this work, we report the genome sequence of Micromonospora lupini Lupac 08 isolated from root nodules of the wild legume Lupinus angustifolious.

Auraticoccus monumenti gen. nov., sp. nov., an actinomycete isolated from a deteriorated sandstone monument.

A Gram-type-positive, strictly aerobic actinobacterium, designated strain MON 2.2(T), was isolated from the surface of a sandstone monument. Cells with a coccoid shape, arranged in pairs or clusters, were non-motile and did not produce spores. The 10 closest 16S rRNA gene sequence matches (~95 % similarity) found in the public databases were uncultured actinobacteria, while the closest cultured members indicated a phylogenetic relationship with members of the family Propionibacteriaceae (92-95 % similarity). Subsequent phylogenetic analysis placed the new isolate within the radiation of the genera Friedmanniella and Microlunatus, but forming an independent branch. Chemotaxonomic markers were consistent with the classification of strain MON 2.2(T) in the family Propionibacteriaceae, amongst the genera containing ll-diaminopimelic acid in their peptidoglycan. Characteristic fatty acids iso-C(15 : 0) and anteiso-C(15 : 0) also supported its affiliation to this taxon; however, polar lipid and menaquinone compositions clearly differentiated strain MON 2.2(T) from other genera in the family. On the basis of these results and additional physiological data obtained in the present study, it is proposed that strain MON 2.2(T) be classified in a novel species in a new genus, for which the name Auraticoccus monumenti gen. nov., sp. nov. is proposed. The type strain of Auraticoccus monumenti is MON 2.2(T) ( = CECT 7672(T)  = DSM 23257(T)  = LMG 25551(T)).

Abyssomicin I, a modified polycyclic polyketide from Streptomyces sp. CHI39.

Abyssomicin I (1), a new modified polycyclic polyketide, was isolated from the culture extract of a soil-derived Streptomyces sp. The structure of 1 was elucidated by interpretation of NMR and other spectroscopic data. The stereochemistry of the new compound was assigned by NOE analysis, chemical derivatization, and application of the modified Mosher method. While 1 was inactive against bacteria and yeasts, the oxidized derivative 7 showed weak activities against gram-positive bacteria. Compounds 1 and 7 exhibited inhibitory effects on tumor cell invasion with IC(50) values of 11 and 0.21 µM, respectively.

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

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 orange-pigmented 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.

Amycolatopsis tucumanensis sp. nov., a copper-resistant actinobacterium isolated from polluted sediments.

A novel actinomycete strain, ABO(T), isolated from copper-polluted sediments showed remarkable copper resistance as well as high bioaccumulation abilities. Classical taxonomic methods, including chemotaxonomy and molecular techniques, were used to characterize the isolate. Strain ABO(T) developed a honey-yellow substrate mycelium on all ISP media tested. Abundant, white, aerial mycelium was only formed on ISP 2, 5 and 7 and MM agar. Both types of hyphae fragmented into squarish rod-shaped elements. The aerial mycelium displayed spore-like structures with smooth surfaces in long, straight to flexuous chains. The organism has a type-IV cell wall lacking mycolic acids and type-A whole-cell sugar pattern (meso-diaminopimelic acid, arabinose and galactose) in addition to a phospholipid type-II profile. 16S rRNA gene sequence studies indicated that this organism is a member of the family Pseudonocardiaceae and that it forms a monophyletic clade with Amycolatopsis eurytherma NT202(T). The DNA-DNA relatedness of strain ABO(T) to A. eurytherma DSM 44348(T) was 39.5 %. It is evident from these genotypic and phenotypic data that strain ABO(T) represents a novel species in the genus Amycolatopsis, for which the name proposed is Amycolatopsis tucumanensis sp. nov. The type strain is ABO(T) (=DSM 45259(T) =LMG 24814(T)).

Promicromonospora kroppenstedtii sp. nov., isolated from sandy soil.

A new actinobacterial strain, RS16(T), was isolated from sandy soil collected in Zamora, Spain, and was studied to determine its taxonomic position. A neighbour-joining tree based on 16S rRNA gene sequence analysis revealed that the novel isolate formed an independent branch between Promicromonospora sukumoe DSM 44121(T) and Promicromonospora citrea DSM 43110(T). Levels of 16S rRNA gene sequence similarity between the novel isolate and its phylogenetic neighbours ranged from 98.7 to 98.9 %. Chemotaxonomic properties, such as the predominant menaquinone and polar lipids, supported the assignment of the novel isolate to the genus Promicromonospora, however, a significant number of physiological differences were found between the novel isolate and the other recognized species of the genus Promicromonospora. On the basis of these results, it is proposed that strain RS16(T) represents a novel species of the genus Promicromonospora, for which the name Promicromonospora kroppenstedtii sp. nov. is proposed. The type strain is RS16(T) (=DSM 19349(T)=LMG 24382(T)).