Antagonistic activity of endophytic actinobacteria from native potatoes (Solanum tuberosum subsp. tuberosum L.) against Pectobacterium carotovorum subsp. carotovorum and Pectobacterium atrosepticum

Background The native potatoes (Solanum tuberosum subsp. tuberosum L.) grown in Chile (Chiloé) represent a new, unexplored source of endophytes to find potential biological control agents for the prevention of bacterial diseases, like blackleg and soft rot, in potato crops. Result The objective of this study was the selection of endophytic actinobacteria from native potatoes for antagonistic activity against Pectobacterium carotovorum subsp. carotovorum and Pectobacterium atrosepticum, and their potential to suppress tissue maceration symptoms in potato tubers. This potential was determined through the quorum quenching activity using a Chromobacterium violaceaum ATCC 12472 Wild type (WT) bioassay and its colonization behavior of the potato plant root system (S. tuberosum) by means of the Double labeling of oligonucleotide probes for fluorescence in situ hybridization (DOPE-FISH) targeting technique. The results showed that although Streptomyces sp. TP199 and Streptomyces sp. A2R31 were able to inhibit the growth of the pathogens, only the Streptomyces sp. TP199 isolate inhibited Pectobacterium sp. growth and diminished tissue maceration in tubers (p ≤ 0.05). Streptomyces sp. TP199 had metal-dependent acyl homoserine lactones (AHL) quorum quenching activity in vitro and was able to colonize the root endosphere 10 days after inoculation. Conclusions We concluded that native potatoes from southern Chile possess endophyte actinobacteria that are potential agents for the disease management of soft rot and blackleg.

Bioactive compounds and molecular diversity of endophytic actinobacteria isolated from desert plants

With the aim to find endophytic actinomycetes that synthesize bioactive compounds over 800 strains were isolated from 53 desert plants of the Gobi-Sumber, Umnugobi, Dundgobi, Dornogobi, Bayankhongor, and Gobi-Altai provinces of Mongolia. The HPLC study of strains with high anti-quorum sensing and antibacterial activities revealed that they produced flavonoids and phenolic compounds. Molecular diversity evaluated with 16S rRNA gene sequences of 123 strains showed that they belonged to 12 genera: Streptomyces, Promicromonospora, Micromonospora, Streptosporangium, Kribbella, Pseudonocardia, Nocardia, Micromonospora, Saccharothrix, Friedmanniella, Actinocatenispora, and Geodermatophilus, the latter two genera were registered in Mongolia for the first time. Moreover, the genus Actinocatenispora was isolated from plants for the first time.

Adaptation to Endophytic Lifestyle Through Genome Reduction by Kitasatospora sp. SUK42

Endophytic actinobacteria offer great potential as a source of novel bioactive compounds. In order to investigate the potential for the production of secondary metabolites by endophytes, we recovered a filamentous microorgansism from the tree Antidesma neurocarpum Miq. After phenotypic analysis and whole genome sequencing we demonstrated that this organism, SUK42 was a member of the actinobacterial genus Kitasatospora. This strain has a small genome in comparison with other type strains of this genus and has lost metabolic pathways associated with Stress Response, Nitrogen Metabolism and Secondary Metabolism. Despite this SUK42 can grow well in a laboratory environment and encodes a core genome that is consistent with other members of the genus. Finally, in contrast to other members of Kitasatospora, SUK42 encodes saccharide secondary metabolite biosynthetic gene clusters, one of which with similarity to the acarviostatin cluster, the product of which displays α-amylase inhibitory activity. As extracts of the host plant demonstrate this inhibitory activity, it suggests that the potential medicinal properties of A. neurocarpum Miq might be provided by the endophytic partner and illustrate the potential for exploitation of endophytes for clinical or industrial uses.

Pancreatic Lipase Inhibitory Activity of Endophytic Actinobacteria from Rhododendron spp.

Antiobesity medication is available as therapeutic compounds that can reduce fat digestion by the inhibition of pancreatic lipase. Actinobacteria have the potency as source of bioactive compounds with various biological function including as pancreatic lipase inhibitor. However, the potency of endophytic actinobacteria from Rhododendron spp. as source of pancreatic lipase inhibitor producer has not been reported yet. The aim of this study was to examine the potential of pancreatic lipase inhibitory activity of 23 endophytic actinobacteria from Rhododendron spp.; to characterize their colony based on morphology and molecular analysis. Screening test of pancreatic lipase inhibitor was conducted using the supernatant of endophytic actinobacteria, lipase pancreatic porcine (L3126) and p-nitrophenyl butyrate. The supernatant of selected isolates was extracted using ethyl acetate. The result showed that various inhibitory activities ranging between 0.00 until 91.69%. There were 11 out of 23 isolates that have potential as pancreatic inhibitor. Amongst them, the extract of four selected isolates, i.e. RZP 1.3, RSSB 3.2, RSS 2.1, and RJB F3.2 demonstrated inhibitory percentage of more than 80%. The RJB F3.2 extract showed to have IC50 value by 431.48 µg mL-1 compared to control, i.e. Xenical (89.07 µg mL-1). Phytochemical analysis exhibited that the extract of the selected isolates contained alkaloid which may function as pancreatic lipase inhibitor. Based on the morphological character, the selected isolates have various morphological colonies and 16S rRNA gene sequence revealed the sequence homology to Streptomyces spp. The data clearly indicate that endophytic actinobacteria from Rhododendron spp. have potency as pancreatic lipase inhibitor producer and further studies could be explored for the development of antiobesity agent.

Characterization of Root-Endophytic Actinobacteria From Cactus (Opuntia Ficus-Indica) for Plant Growth Promoting Traits

The present study is the first report of isolation and characterization of endophytic actinobacteria from cactus (Opuntia ficus-indica). A total of 179 morphologically distinct endophytic actinobacterial isolates were purified from the roots of two different genetic accessions of cactus. All these isolates were screened for their plant growth promotion traits namely growth on N-free medium, P-solubilization, siderophore production, ACC deaminase activity and IAA production. A majority of the endophytic actinobacterial isolates (85%) exhibited the potential for plant growth promotion under in vitro conditions. Ten among the isolates were selected based on their multi-PGP traits and were identified as Streptomyces sp. based on the 16S rRNA gene sequencing and phylogenetic analysis. Plant growth promoting potential of these selected endophytic Streptomyces was studied in wheat seedlings. All these selected isolates significantly enhanced the growth parameters like seedling length and rootlets number compared to the uninoculated control. The wheat seeds inoculated with Streptomyces tuirus VL-70-IX exhibited maximum number of rootlets (6.33) compared to uninoculated control (3.67). The inoculation of endophytic actinobacteria Streptomyces pseudogriseolus VL-70-XII caused maximum seedling length (20.53 cm) and root length (8.26 cm) while the inoculation of S. radiopugnans HV-VIII resulted in highest shoot length (12.33 cm). These endophytic actinobacteria isolated from the roots of cactus accessions showed potential PGP traits. This work lays foundation for characterization and selection of endophytic actinobacteria from the under-exploited, drought tolerant species such as cactus with potential cross-compatibility for the improvement of plant growth of field crops especially under abiotic stress conditions..