Isolation and Identification of Actinobacteria from Surface-Sterilized Wheat Roots

Abstract

This is the first report of filamentous actinobacteria isolated from surface-sterilized root tissues of healthy wheat plants (Triticum aestivum L.). Wheat roots from a range of sites across South Australia were used as the source material for the isolation of the endophytic actinobacteria. Roots were surface-sterilized by using ethanol and sodium hypochlorite prior to the isolation of the actinobacteria. Forty-nine of these isolates were identified by using 16S ribosomal DNA (rDNA) sequencing and found to belong to a small group of actinobacterial genera including Streptomyces, Microbispora, Micromonospora, and Nocardiodes spp. Many of the Streptomyces spp. were found to be similar, on the basis of their 16S rDNA gene sequence, to Streptomyces spp. that had been isolated from potato scabs. In particular, several isolates exhibited high 16S rDNA gene sequence homology to Streptomyces caviscabies and S. setonii. None of these isolates, nor the S. caviscabies and S. setonii type strains, were found to carry the nec1 pathogenicity-associated gene or to produce the toxin thaxtomin, indicating that they were nonpathogenic. These isolates were recovered from healthy plants over a range of geographically and temporally isolated sampling events and constitute an important plant-microbe interaction.The actinobacteria have been well characterized in the literature due to their economic importance as producers of two-thirds of the microbially derived antibiotics known today (6, 23). The actinobacteria are characterized by their grampositive nature and high guanine-plus-cytosine (GϩC) content in their genomes. Ecologically, actinobacteria and, particularly, the Streptomyces spp. are generally saprophytic, soil-dwelling organisms that spend the majority of their life cycles as semidormant spores (27). It has also been demonstrated that actinobacteria inhabit the rhizosphere of many plant species, including cereal crops such as wheat (13,15,30,37).Some actinobacteria are also known to form more intimate associations with plants and colonize their internal tissues. Within the order Actinomycetales there are examples of both endophytic and plant-pathogenic species. The best-characterized examples of the plant-pathogenic actinobacteria are the potato scab-causing Streptomyces scabies, S. acidiscabies, and S. turgidiscabies. Pathogenicity has been associated with the presence of a conserved and transmissible pathogenicity island (PAI) in their genomes (9, 21). This PAI encodes for the biosynthesis of a phytotoxin, thaxtomin, and also contains plant virulence factor genes such as nec1 (8,22,26). Actinorhizae (Frankia spp.) have been extensively researched as an endophytic association between a plant and an actinobacterium (for reviews, see references 3, 4, and 5). However, examples of actinobacteria other than Frankia inhabiting the root tissues of healthy plants as endophytes are rare. Sardi et al. (35) reported the presence of actinobacteria in root samples of crops and Italian native plants, with the majority of the isolates be...

Isolation and characterization of culturable endophytic actinobacteria associated with Artemisia annua L.

“…It can be considered that the various isolation methods employed in this study were productive and resulted in the successful isolation of numerous endophytic actinobacteria. The first method used is the simplest and most commonly used (Coombs and Franco 2003;Qin et al 2009). This method was used for selectively isolating fast-growing streptomycetes and other actinobacteria, but there was some interference from contaminating fungi.…”

“…Endophytic actinobacteria, as one of the significant residents in plant tissues, have attracted more attention in recent years since there is an ever increasing need for novel organisms and their bioactive products. There have been numerous reports focusing on these useful microorganism, which have been isolated from diverse economic plants such as wheat (Coombs and Franco 2003), rice (Tian et al 2007), potato (Sessitsch and Berg 2004), carrots (Surette et al 2003), tomato, rape (Nejad and Johnson 2000) and citrus (Araujo et al 2002) and various medicinal plants (Taechowisan et al 2003;Zin et al 2007;Li et al 2008;Qin et al 2009). These organisms seem to have important roles in plant development and health because they can promote plant growth by nutrient assimilation or phytohormone production.…”

Biodegradation of melamine and its hydroxy derivatives by a bacterial consortium containing a novel Nocardioides species

“…No pathogenicity to plants or animals has currently been reported in any species of the genus Nocardioides. They are often isolated as plant endophytes and are known to be capable of suppressing crop pathogens (Coombs and Franco 2003;Carrer Filho et al 2008). In comparison with other known melamine-degrading bacteria, strain ATD6 is expected to be the most useful candidate of the tool in the safe bioremediation of a melaminecontaminated farmland.…”

Micromonospora terminaliae sp. nov., an endophytic actinobacterium isolated from the surface-sterilized stem of the medicinal plant Terminalia mucronata

“…Extraction of genomic DNA from strain TMS7 T and amplification and sequencing of the 16S rRNA gene were carried out as described previously [19]. The resultant 16S rRNA gene sequence of TMS7 T was analysed using the EzTaxon-e server [20] and subsequently aligned with the 16S rRNA gene sequences of representatives of all the recognized strains of the genus Micromonospora available from GenBank/EMBL by using CLUSTAL X [21] with Actinoplanes philippinensis IFO 13878 T as the outgroup.…”