BIODEGRADATION POTENTIAL OF RHIZOSPHERIC MICROORGANISMS OF RHIZOPHORA RACEMOSA IN CRUDE OIL CONTAMINATED MANGROVE SWAMP IN THE NIGER DELTA

Rhizophora racemosa (red mangrove tree) belongs to the family Rhizophoraceae; it is an important constituent of the mangrove swamp in Niger Delta, an oil producing region in Nigeria. The remediation of soils containing organic pollutants is possible with the use of microbial communities when the ecology is understood for potentials maximization. This study investigated the biodegradation potential of rhizospheric microorganisms of Rhizophora racemosa in crude oil- contaminated mangrove swamp in the Niger Delta.The total microbial count was determined by the serial dilution method. The hydrocarbon-utilizing bacteria and fungi were enumerated using Mineral Salts Agar containing crude oil as the sole carbon source. The biodegradation potential of these rhizomicrobes was determined using screen test, shake flask degradation tests, Total Organic Gas (TOG) and Total Petroleum Hydrocarbon (TPH) InfraCal Analyzer (HATR-T2 and CH). The turbidity, total organic gas (TOG-N) and total petroleum hydrocarbon were measured weekly for twenty-eight days. Hydrocarbon-degrading microbes isolated from the rhizosphere were identified as Marinococcus sp., Azotobacter sp., Acinetobacter sp. Aspergillus niger, Aspergillus flavus and Candida albicans. The highest rate of TPH reduction was recorded in Acinetobacter sp. (from 150 mg/L on day 1 to ˂0.0031 mg/L on day 14). This was followed by Candida albicans (148mg/L on day 1 to 2.68mg/L on day 28) and Aspergillus flavus (150mg/L on day 1 to 4.21mg/L on day 28) In conclusion, it can be inferred that the some rhizospheric microbes of Rhizophora racemosa can efficienctly degrade hydrocarbon up to 100% rate over a period of 28 days.

Effect of Natural Polysaccharide Matrix-Based Selenium Nanocomposites on Phytophthora cactorum and Rhizospheric Microorganisms

We studied the effects of new chemically synthesized selenium (Se) nanocomposites (NCs) based on natural polysaccharide matrices arabinogalactan (AG), starch (ST), and kappa-carrageenan (CAR) on the viability of phytopathogen Phytophthora cactorum, rhizospheric bacteria, and potato productivity in the field experiment. Using transmission electron microscopy (TEM), it was shown that the nanocomposites contained nanoparticles varying from 20 to 180 nm in size depending on the type of NC. All three investigated NCs had a fungicidal effect even at the lowest tested concentrations of 50 µg/mL for Se/AG NC (3 µg/mL Se), 30 µg/mL for Se/ST NC (0.5 µg/mL Se), and 39 µg/mL for Se/CAR NC (1.4 µg/mL Se), including concentration of 0.000625% Se (6.25 µg/mL) in the final suspension, which was used to study Se NC effects on bacterial growth of the three common rhizospheric bacteria Acinetobacter guillouiae, Rhodococcus erythropolis and Pseudomonas oryzihabitans isolated from the rhizosphere of plants growing in the Irkutsk Region. The AG-based Se NC (Se/AG NC) and CAR-based Se NC (Se/CAR NC) exhibited the greatest inhibition of fungal growth up to 60% (at 300 µg/mL) and 49% (at 234 µg/mL), respectively. The safe use of Se NCs against phytopathogens requires them to be environmentally friendly without negative effects on rhizospheric microorganisms. The same concentration of 0.000625% Se (6.25 µg/mL) in the final suspension of all three Se NCs (which corresponds to 105.57 µg/mL for Se/AG NC, 428.08 µg/mL for Se/ST NC and 170.30 µg/mL for Se/CAR NC) was used to study their effect on bacterial growth (bactericidal, bacteriostatic, and biofilm formation effects) of the three rhizospheric bacteria. Based on our earlier studies this concentration had an antibacterial effect against the phytopathogenic bacterium Clavibacter sepedonicus that causes diseases of potato ring rot, but did not negatively affect the viability of potato plants at this concentration. In this study, using this concentration no bacteriostatic and bactericidal activity of all three Se NCs were found against Rhodococcus erythropolis based on the optical density of a bacterial suspension, agar diffusion, and intensity of biofilm formation, but Se/CAR and AG NCs inhibited the growth of Pseudomonas oryzihabitans. The cell growth was decrease by 15–30% during the entire observation period, but the stimulation of biofilm formation by this bacterium was observed for Se/CAR NC. Se/AG NC also had bacteriostatic and antibiofilm effects on the rhizospheric bacterium Acinetobacter guillouiae. There was a 2.5-fold decrease in bacterial growth and a 30% decrease in biofilm formation, but Se/CAR NC stimulated the growth of A. guillouiae. According to the results of the preliminary field test, an increase in potato productivity by an average of 30% was revealed after the pre-planting treatment of tubers by spraying them with Se/AG and Se/CAR NCs with the same concentration of Se of 0.000625% (6.25 µg/mL) in a final suspension. The obtained and previously published results on the positive effect of natural matrix-based Se NCs on plants open up prospects for further investigation of their effects on rhizosphere bacteria and resistance of cultivated plants to stress factors.

Morphological study of potassium solubilizers

Potassium is an elementary macronutrient besides Nitrogen and Phosphorus for growth of plants. It performs crucial metabolic activities like photosynthesis, activation of enzyme and protein synthesis. Rhizospheric microorganisms are the keysegments of viable agricultural ecosystems.These perform a vital characterbyresolving the unobtainable Potassium form and make accessible forroots of plants. Potassium concentrations which are soluble in the soil are generally less though above 90% Potassium present in the soil subsist in the form of insoluble rock. Solubilization of a certain configuration of K is done by effective K-solubilizers treatment to an obtainable structure of K in the soil. The obtained form of K should be simply absorbed by the plant. Some selected bacterial and fungal isolates based on their morphological characteristics were assessed for their potentiality to resolve K from insolvable K trace. The selected isolates were in the form of rods, Gram positive and motile. This review assays on the morphological study of K-solubilizers for their remarkable supremacy in forming zone of solubilization.

Comparative Study of the Rhizospheric Microflora of Sunflower Cultivars Helianthus annuus (Asteráceae, Magnoliópsida) Grown on Soils with Anthropogenic Polyelemental Anomalies

In a laboratory pot experiment, two mutant cultivars of sunflower (Helianthus annuus cv. r2p2 and Helianthus annuus cv. r5n1) were grown on soils with anthropogenic polyelemental anomalies and on a background control soil, and a comparative analysis of their rhizospheric microflora was carried out. The numbers of soil bacteria, actinomycetes and micromycetes, as well as the numbers of rhizospheric microorganisms resistant to Zn2+, Pb2+, and Cu2+ ions were estimated in the rhizosphere of sunflower cultivars. Quantitative changes in the sunflower rhizospheric microboceno-ses, formed under the influence of both the plant genotype and technogenic soil pollution, were revealed. A pronounced stimulation of the rhizospheric microorganisms of all groups studied was found when plants were cultivated on the technogenically contaminated soil from PJSC Kosogorsk Metallurgical Plant. In this case, cultivar differences were observed, namely: the maximal number of bacteria and actinomycetes was revealed in the rhizosphere of H. annuus cv. r2p2, whilst the maximal number of micromycetes was revealed in the rhizosphere of H. annuus cv. r5n1. An increased number of microorganisms resistant to lead ions was revealed in the rhizosphere of H. annuus cv. r2p2. The observed changes in the structure of rhizospheric microbial communities of the sunflower cultivars manifested in the stimulation of the growth and activity of soil microflora can be in demand for phytoremediation of technogenically contaminated soil.

The effect of oil pollution on the activity of physiological and biochemical processes in Triticum aestivum L. and the number of rhizospheric microbiota

The article presents the results of a study of the effect of oil pollution on the biochemical and morphometric parameters of the plant Triticum aestivum L., as well as a change in the number of rhizospheric microorganisms capable of degradation of petroleum hydrocarbons. It was shown that under the influence of pollution in plants increased the activity of redox enzymes. A significant increase in hydrocarbon-oxidizing bacteria and fungi was recorded in the rhizosphere.

Using nod genes control system to create rhizospheric microorganisms with regulated gene expression

Inducible vector containing the full-sized nodD gene and the promoter region of the nod-box under the control of which was cloned the gfp gene was constructed. Modified bacteria R. galegae in which the synthesis of GFP protein was activated by plant flavonoids were obtained.

Artificial symbioses of plants and microorganisms

The report discusses the problems of creating artificial associations of cultivated plants and rhizobia using plant and bacterial adhesins, as well as systems of controlled synthesis of growth-promoting substances by rhizospheric microorganisms.