Lecturer, Ahmadu Bello University, Zaria, Nigeria
This study focuses on the ability of members of the bacterial group, Actinobacteria, to produce secondary metabolites (antibiotics) against some selected bacteria and fungi known to cause disease in humans. The Actinobacteria are a filamentous group of bacteria that produce branching hyphae like fungi, they are known for their extensive production of many antibiotics. However, a few of them cause disease in humans and animals. The rhizosphere is the region of soil surrounding the root of plants. It is known to be a good source of beneficial bacteria such as, the symbiotic Nitrogen-fixing bacteria as well as actinobacteria. In this research, actinobacteria were isolated from soil collected from ginger rhizosphere and refuse dump sites, and their ability to stop the growth of disease causing microorganisms was assessed. This ability was determined by measuring the zones of inhibition observed when disease-causing bacteria were grown in the presence of actinobacteria in laboratory media. The larger the zone of inhibition (in millimetres), the more potent the antimicrobial activity of the actinobacteria. It was observed that the actinobacteria had antagonistic effect on the bacteria tested but not the fungi. Also, a high percentage of the bacteria isolated (70%) was able to stop the growth of the bacteria tested. However, the bacteria isolated from the ginger rhizosphere showed a higher degree of antimicrobial activity compared to the actinobacteria isolated from refuse dump soil. Thus, proving that the rhizosphere is a "hotspot" for microorganisms with medical as well as industrial importance.
Abstract: The root parasitic weed Orobanche cumana (sunflower broomrape) constrains sunflower (Helianthus annuus L.) production in many areas of the world. A seed germination experiment, a co-culture experiment, and a pot experiment were conducted to study the effect of some soilborne antagonistic microorganisms on O. cumana. Results showed that culture filtrate of Streptomyces enissocaesilis significantly reduced the germination rate of O. cumana seeds both in the seed germination experiment and the co-culture experiment, with more than 50 and 40 % (after cultivation for eight days) reduction respectively over the control. In the pot experiment, applying S. enissocaesilis reduced the epigaeous number of O. cumana tubercles by 47.5 % after 130 days. Furthermore, S. enissocaesilis also increased polyphenol oxidase activity in sunflower roots and improved the beneficial microflora in the rhizosphere soil of sunflower. Selecting biocontrol agents from soilborne antagonistic microorganisms might be a promising strategy for controlling O. cumana.
Pub.: 23 Apr '16, Pinned: 27 Nov '17
Abstract: The experiment was conducted with an objective to survey potential black pepper growing tracts of Kerala and Karnataka for the isolation and characterization of rhizosphere actinobacterial strains for exploiting its antagonistic potential against major pathogens of black pepper as well as for growth promotion. Accordingly fifty actinobacterial strains were isolated and were morphologically characterized and studied for its antagonism against major soil borne pathogens of black pepper viz., Phytophthora capsici and Sclerotium rolfsii. Three isolates (IISRBPAct1, IISRBPAct25 and IISRBPAct42) showed more than 90% inhibition against the targeted pathogens. The isolate IISRBPAct1 showed 91-94% inhibition to both of the pathogens followed by IISRBPAct42 (68-94%) and IISRBPAct25 (86-90%). The potential isolates were characterized morphologically using light microscopy and Scanning Electron Microscopy (SEM). Molecular characterization was done by 16S-rDNA sequencing using two sets of actinomycetes specific primers viz., 1) S-C-Act-235-S-20 and S-C-Act-878-A-19 and 2) 27f and1525r were identified as belonging to Streptomyces sp. The isolates exhibited production of different hydrolytic enzymes such as amylases, proteases, lipases, and cellulases. Further the isolates were evaluated for their Plant Growth Promoting (PGP) traits and biocontrol traits such as production of Indole Acetic Acid (IAA) and siderophores. IISRBPAct1 showed production of both IAA and siderophore while IISRBPAct25 and IISRBPAct42 produced only siderophore. In planta experiment was conducted to evaluate the growth promotion activity as well as pathogen suppression. Out of the three potential Streptomyces spp IISRBPAct1 showed maximum growth promotion in terms of shoot biomass, shoot height and number of laterals where as maximum root biomass was observed with IISRBPAct 42. Highest reduction of disease incidence was observed on treatment with IISRBPAct1 (98.10%) against Sclerotium rolfsii while IISRBPAct25 showed highest reduction of foot rot incidence (80.73%). The results of the study clearly revealed the biocontrol and PGPR properties of three Streptomyces sp. which can be developed as potential candidates for the biological control of major black pepper pathogens.
Pub.: 09 Mar '17, Pinned: 27 Nov '17
Abstract: Plants adapt to metal stress by modifying their metabolism including the production of secondary metabolites in plant tissues. Such changes may impact the diversity and functions of plant associated microbial communities. Our study aimed to evaluate the influence of metals on the secondary metabolism of plants and the indirect impact on rhizosphere bacterial communities. We then compared the secondary metabolites of the hyperaccumulator Pteris vittata L. collected from a contaminated mining site to a non-contaminated site in Vietnam and identified the discriminant metabolites. Our data showed a significant increase in chlorogenic acid derivatives and A-type procyanidin in plant roots at the contaminated site. We hypothesized that the intensive production of these compounds could be part of the antioxidant defense mechanism in response to metals. In parallel, the structure and diversity of bulk soil and rhizosphere communities was studied using high-throughput sequencing. The results showed strong differences in bacterial composition, characterized by the dominance of Proteobacteria and Nitrospira in the contaminated bulk soil, and the enrichment of some potential human pathogens, i.e., Acinetobacter, Mycobacterium, and Cupriavidus in P. vittata's rhizosphere at the mining site. Overall, metal pollution modified the production of P. vittata secondary metabolites and altered the diversity and structure of bacterial communities. Further investigations are needed to understand whether the plant recruits specific bacteria to adapt to metal stress.
Pub.: 02 Jun '17, Pinned: 27 Nov '17
Abstract: Insecticidal proteins expressed by genetically modified Bt maize may alter the enzymatic and microbial communities associated with rhizosphere soil. This study investigated the structure and enzymatic activity of rhizosphere soil microbial communities associated with field grown Bt and non-Bt maize. Rhizosphere soil samples were collected from Bt and non-Bt fields under dryland and irrigated conditions. Samples were subjected to chemical tests, enzyme analyses, and next generation sequencing. Results showed that nitrate and phosphorus concentrations were significantly higher in non-Bt maize dryland soils, while organic carbon was significantly higher in non-Bt maize irrigated field soil. Acid phosphatase and β-glucosidase activities were significantly reduced in soils under Bt maize cultivation. The species diversity differed between fields and Bt and non-Bt maize soils. Results revealed that Actinobacteria, Proteobacteria, and Acidobacteria were the dominant phyla present in these soils. Redundancy analyses indicated that some chemical properties and enzyme activities could explain differences in bacterial community structures. Variances existed in microbial community structures between Bt and non-Bt maize fields. There were also differences between the chemical and biochemical properties of rhizosphere soils under Bt and non-Bt maize cultivation. These differences could be related to agricultural practices and cultivar type.
Pub.: 22 Jul '17, Pinned: 27 Nov '17