A Consolidated Method for Selective Isolation of Actinomycetes Based on Choice of Substrate

Actinomycetes are known as filamentous, Gram positive bacteria. They form the majority of the microbial load in various niches; soils, composts, etc. The study aimed to evaluate the method of isolating slow growing actinomycetes from four different sources: garden soil, cow dung manure compost, floral waste compost, and floral waste vermicompost. In this study, an integrated method consisting of physical and chemical pretreatment of the sample and the use of selective media was used to isolate actinomycetes. Physical treatment includes air drying, sun drying, dry heating in an oven, and moist heat treatment, whereas chemical treatment includes enrichment of the sample with CaCO3 followed by plating on actinomycetes-specific media with the incorporation of antibacterial and antifungal antibiotics. The actinomycetes count on the plate was reported in CFU/gm of dry wt. Morphological and microscopic characteristics of purified isolates were noted. The results were compared, and it was found that the pretreatment method of a particular sample depends on the choice of substrate. Overall, physical treatment followed by chemical enrichment showed relatively higher counts on the plate and better results. Here we also found the dominance of fluorescent Pseudomonas sp. in case samples from vermicompost. The study can be of great importance in isolating novel and rare genera of actinomycetes. These methods can help speed up the isolation and screening of novel actinomycetes which will ultimately be important for the discovery of antibiotics and other industrially vital bioactive compounds.

Antagonistic activity of rice rhizosphere isolates against Xanthomonas oryzae pv. oryzae bacterial blight pathogen

Attempts were made to isolate beneficial bio agents from rice rhizosphere which resulted in isolation of 46 Bacillus spp and 15 fluorescent Pseudomonas spp which were further investigated for their potential aginst BB of rice diseaseAmong twenty six isolates of Bacillus, two isolates were most antagonistic and showed highest inhibition percentage (57.09) The potential isolates of Pseudomonas (P-4, P-5, P-6, P-7 and P-8), Bacillus (ARI 1-2, ARI 2-4, ARI 1-3, D1-1-2 and D2-1-1) were tested in vivo under glass house conditions for antagonism against Xoo which revealed that P-7 was effective in reduction of lesion length (18.5cm) when compared to control (20.37cm). The potential isolates of Pseudomonas (P-4, P-5, P-6, P-7 and P-8), Bacillus (ARI 1-2, ARI 2-4, ARI 1-3, D1-1-2 and D2-1-1) were tested in vivo under glass house conditions for antagonism against Xoo which revealed that P-7 was effective in reduction of lesion length (18.5cm) when compared to control (20.37cm). The present study indicated that PGPR isolates P-4, P-6, P-7 and P-8 can be used as biofertilizers, which will add up for enhanced growth of rice.

Effect of growth forms of bamboo on the mycorrhizal and fluorescent pseudomonas population

Bamboo, also called as the poor man’s timber, is one of the fastest growing giant grass species. Having shallow root system and fast growth rate, the dependability of the plant on the rhizospheric microbial web cannot be denied. The study was conducted to explore the population and seasonal variations of indigenous mycorrhizal fungi as well as the functional diversity of plant growth promoting bacteria, especially fluorescent pseudomonas from the different growth forms of Dendrocalamus strictus, the most commonly present bamboo species in Indian sub-continent. In a past study, it was established that the growth forms of D. strictus which developed over time in their respective locations, were genetically varied. The present research further explores the variations in their respective rhizospheric microbes and looks for the role of plant selection phenomenon. Considerable variation in mycorrhizal structures and in the functional diversity of fluorescent pseudomonas was registered. It seems probable that selection pressure of nutrient deficient condition has created a condition that promoted occurrence of high numbers of P solubilisers which, in turn, boosted the mycorrhizal as well as bamboo growth.

Influence of fluorescent Pseudomonas on the growth of Mimosa scabrella seedlings

Bracantiga (Mimosa scabrella Benth) is a native leguminous specie from the south of Brazil, with great potential for commercial use. It can be used to recover degraded areas due to their fast growth, high adaptability and root nodule formation capacity. One alternative to reduce fertilization costs of seedlings production, are the plant growth promoting rhizobacteria. The fluorescent group of Pseudomonas is common at several plant rhizosphere. The objective of this work was to assess the growth stimulus of fluorescent Pseudomonas isolates at bracatinga seedlings. The seeds were inoculated with three bacterial isolates (CBSAL14, CBSAL18 and CBSAL05), genetically identified as Pseudomonas sp. They were previously grown in 50 mL of Luria Bertani medium for 48 h and then the seeds were submerged for 30 min in the suspensions. Subsequently, they were sown in tubes containing sterilized commercial substrate and kept in greenhouse for five months. From 61 days after sowing, seedling height and stem diameter were measured monthly. The CBSAL14 and CBSAL18 isolates promoted promoted increase in growth of seedlings height of inoculated individuals compared to control, suggesting their potential use as plant growth promoters.

Screening and characterization of nutrient solubilizing phytobeneficial rhizobacteria from healthy coconut palms in root (wilt) diseased tract of Kerala, India

Aim: Isolation, screening and characterization of beneficial rhizosphere bacteria associated with healthy (field-resistant) coconut palms in root (wilt) disease endemic hotspot areas of Kerala. Methodology: One hundred and ten rhizobacterial isolates associated with healthy coconut palms of root (wilt) diseased tract of Kerala were isolated and screened in-vitro for IAA production and solubilization of fixed forms of mineral nutrients. Seven isolates showing multiple phytobeneficial properties were characterized and the selected isolate was tested for its biopriming effect on maize. Results: Of the total isolates screened, 54 isolates produced IAA. Among the nutrient solubilizers, silicate solubilizers (57%) and phosphate solubilizers (48%) dominated. Of the seven isolates with multiple phytobeneficial properties, five rhizobacterial isolates belonged to Enterobacteriaceae family including three Enterobacter spp. The isolate T4HFB9 belonged to Acinetobacter sp. The green fluorescent Pseudomonas isolate K3HPSB2, showed 99% sequence similarity with Pseudomonas migulae. Seed biopriming of maize with Pseudomonas sp. strain K3HPSB2 recorded significant increase in germination percentage and seedling vigour index over untreated control. Interpretation: Disease-resistant coconut palms in RWD endemic tracts host a good proportion of phytobeneficial rhizosphere bacteria,with demonstrable multiple plant growth promoting traits. Multi-nutrient solubilizing Pseudomonas sp. with bioinoculant prospects has been selected for further studies on bio-priming for palm health management in RWD endemic tracts.

A Cross-Metabolomic Approach Shows that Wheat Interferes with Fluorescent Pseudomonas Physiology through Its Root Metabolites

Roots contain a wide variety of secondary metabolites. Some of them are exudated in the rhizosphere, where they are able to attract and/or control a large diversity of microbial species. In return, the rhizomicrobiota can promote plant health and development. Some rhizobacteria belonging to the Pseudomonas genus are known to produce a wide diversity of secondary metabolites that can exert a biological activity on the host plant and on other soil microorganisms. Nevertheless, the impact of the host plant on the production of bioactive metabolites by Pseudomonas is still poorly understood. To characterize the impact of plants on the secondary metabolism of Pseudomonas, a cross-metabolomic approach has been developed. Five different fluorescent Pseudomonas strains were thus cultivated in the presence of a low concentration of wheat root extracts recovered from three wheat genotypes. Analysis of our metabolomic workflow revealed that the production of several Pseudomonas secondary metabolites was significantly modulated when bacteria were cultivated with root extracts, including metabolites involved in plant-beneficial properties.

Genetic diversity of Pseudomonas syringae pv. syringae isolated from sweet cherry in southern and northern regions in Serbia

Bacterial canker and leaf spot caused by plant pathogenic bacterium Pseudomonas is among the most destructive cherry diseases worldwide. Nowadays in Serbia, sweet cherry production significantly increased and the new plantations, mainly grown from imported planting material are being raised every year. During spring, 2018 and 2019, occurrence of bacterial canker and leaf spot symptoms was observed on a newly planted sweet cherry plantations in two localities, Zitoradja (Southern region) and Karavukovo (Northern region-Vojvodina). Typical P. syringae colonies were isolated on Nutrient Sucrose Agar supplemented with 5% sucrose (NSA). A total of fifteen isolates were selected and identified. Results of the LOPAT test (+---+) determined them to belong to fluorescent Pseudomonas Group Ia, while results of G+A+T-Ta- tests indicate presence of Pseudomonas syringae pv. syringae. Pathogenicity was confirmed on immature sweet and sour cherry fruitlets by forming of black, sunken lesions for all tested isolates. Genes syrB and syrD were successfully detected in all tested isolates. DNA sequencing using gapA, gltA, gyrB and rpoD housekeeping genes determined tested isolates to belong to P. s. pv. syringae using the National Center for Biotechnology Information (NCBI) nucleotide BLAST. The Serbian isolates shared 99.47% to 100% (Zitoradja) and 99.38% to 100% (Karavukovo) identity with bacterium P. s. pv. syringae. Phylogenetic analysis grouped isolates from Zitoradja in one tree cluster, separate from the Karavukovo isolates, indicating presence of two genetically diverse groups of causal pathogen P. s. pv. syringae, obtained from two geographically distinct localities in Serbia. Phylogeographic analysis grouped isolates from Zitoradja in multilocus haplotype coded as REz and isolates originated from Karavukovo in multilocus haplotype coded as REk. Considering that during last few years P. syringae continuously occurs mainly in young sweet cherry plantations, where imported material is used for raising, health status check is recommended to be included as obligatory measure when nursery material is used from import.