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Isolation, Morphological and Biochemical Characterization of Rhizobacteria from Arsenic Contaminated Paddy Soils in Bangladesh: an in Vitro Study

Mohammad Mosharraf Hossain
Department of Soil Science, Sher-e-Bangla Agricultural University, Dhaka, Bangladesh;Department of Soil Science, Bangabandhu Sheikh Mujibur Rahman Agricultural University,Gazipur, Bangladesh.

G. K. M. M. Rahman
Department of Soil Science, Bangabandhu Sheikh Mujibur Rahman Agricultural University,Gazipur, Bangladesh.

M. A. M. Akanda
Department of Plant Pathology, Bangabandhu Sheikh Mujibur Rahman Agricultural University,Gazipur, Bangladesh.

A. R. M. Solaiman
Department of Soil Science, Bangabandhu Sheikh Mujibur Rahman Agricultural University,Gazipur, Bangladesh.

M.T. Islam
Department of Biotechnology, Bangabandhu Sheikh Mujibur Rahman Agricultural University,Gazipur, Bangladesh.

M. M. Rahman
Department of Soil Science, Bangabandhu Sheikh Mujibur Rahman Agricultural University,Gazipur, Bangladesh.

Abstract/ Executive Summary:

Soil-plant–microbes relations within the plant rhizosphere are the determinants of plant and soil health, which is important for soil ecological environment for plant-microbe interactions. Plant growth-promoting rhizobacteria (PGPR) are considered to encourage plant growth and development directly or indirectly in soil. PGPR can demonstrate a diversity of characteristics responsible .for influencing plant growth and development. During this study, Twenty four different bacterial isolates were isolated, and detailed morphological, biochemical, and physiological characterizations of those isolates were accomplished. This experiment was performed with the 24 bacterial isolates to see their gram stain test, KOH test, catalase activity, cellulose degradation capability, indole acetic acid (IAA) production, and phosphate solubilization activities, and also tested for growth within the different arsenic and salt stress conditions and 37°C temperature. Results revealed that among the rhizobacterial isolates, fifteen bacterial isolates were negative and nine were positive in gram reaction, while some were showed high IAA production ability, phosphate solubility capability, and cellulose degradation capacity within the culture media. The isolates were isolated from paddy soils and a few were characterized by a yellow color, flat elevation, and gram-positive, while some were characterized because of the yellowish color with round colony shape, raised elevation, gram-negative, and every one the isolates were positive in catalase production capacity and phosphate solubilization activity which is able to increase the available phosphorus within the soil for plants and also produced indole acetic acid that may use as a hormone to be used in growth enhancement of plants. Hence, these isolates need to be tested further for their effect on arsenic dynamics at the plant rhizosphere, selection of suitable plant species for the bacterial association, bacterial effect on arsenic uptake by plants, and potentials for field applications for sustainable agriculture.

Keywords: Rhizobacteria; Paddy soil; Arsenic;

Location: Soil Microbiology Laboratory of the Department of Soil Science at Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh

Start Date: 00-01-2016

End Date: 00-06-2016

Program Area: Crop-Soil-Water Management

Commodity: Soil Arsenic

Objectives:

To isolate, morphological, and biochemically characterize the rice rhizospheric bacteria from arsenic-contaminated paddy soils.

Methodology:

The experiment was conducted at the Soil Microbiology Laboratory of the Department of Soil Science at Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh during the period from January 2016 to June 2016 to fulfill the abovementioned objective. Soil samples were collected from different sites of arsenic-contaminated paddy fields of Shahrasti Upazila of Chandpur district of Bangladesh located in between 23°08' and 23°17' North latitudes and in between 90°51' and 91°02' East longitudes within the 23°008´ to 23°308´ North latitude and from 90°328´ to 91°028´ East longitude of Chandpur District in Bangladesh. The latitude and longitudes (GPS reading) of the sampling sites were recorded. Soil samples were collected from the rice rhizosphere of different sites of arsenic-contaminated paddy fields randomly and carefully labeled and put in zip lock bags, wrapped in foil paper, and transported to the laboratory, and stored in a refrigerator at 40°C temperature for culturing the bacteria. All the soil sampling points were geo-referenced with the GPS tool. A portion of each sample was mixed, transferred to the laboratory, sun-dried, and passed through a 2 mm sieve, and used for subsequent physical-chemical and microbial analysis. From each soil sample, 1 g of soil was suspended in 9 ml of double-distilled water and vortex for 3 minutes. The resulting suspensions were serially diluted to 10-10. Each dilution (0.1 ml) was spread over a pre-solidified Nutrient Agar (NA) media plates (Beef extract- 10.0 g, NaCl 5.0 g, Peptone 10.0 g, Distilled water 1.0 L, Agar 20.0 g, Adjust pH to 7.0-7.5). In the rhizobacterial isolation process, a solid nutrient-rich agar medium was used and each media was autoclaved at 121°C with 15 psi for 20 minutes before inoculation. After inoculation, the samples were spread over with the help of a sterile spreader and then incubated in an incubator at 28°C for 2 days. Growth was monitored daily and single colonies were picked up with a sterile toothpick and sub-cultured over the pre-solidified NA media. All the subsequent In vitro plate assay analyses were done in triplicate until the colonies were more purified. A serial dilution technique was used to isolate the bacterial population from the soil. From each soil sample, 1 g of soil was suspended in 9 ml of double-distilled water and vortex for 3 minutes. The resulting suspensions were serially diluted to 10-10. Each dilution (0.1 ml) was spread over a pre-solidified Nutrient Agar (NA) media plates (Beef extract- 10.0 g, NaCl 5.0 g, Peptone 10.0 g, Distilled water 1.0 L, Agar 20.0 g, adjust pH to 7.0-7.5). All the physical and chemical properties of collected soil samples were analyzed by standard analytical protocol. Soil pH was measured with the help of a glass electrode pH meter as described by Jackson [30]. Organic carbon was determined following the wet oxidation method as described by Page et al. and the organic matter content was calculated by multiplying the % organic carbon with the Van Bemmelen factor 1.73. Total N of soil was estimated following the micro-Kjeldahl method. The phosphorus in the extract was then determined colorimetrically. The absorbance was measured by a double beam spectrophotometer (Model no. 170-30, Hitachi, Japan) at 710 nm wavelength. Exchangeable potassium of soil was determined from ammonium acetate (1N NH₄OAC) extract as described by Jackson and was measured by using a flame-photometer (Atomic absorption spectrophotometer, model No. Hitachi, Japan). Then total As was determined by using the method as described by Loeppert and Biswas using hydride generation atomic absorption spectrophotometer (HG-AAS).

Source of Information: Asian Journal of Soil Science and Plant Nutrition - 7(2): 41-55, 2021

Article Link (Online Journal): DOI: 10.9734/AJSSPN/2021/v7i230110

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Nowadays, soil contamination by arsenic is a major hazard in Bangladesh. The necessity to develop cost-effective and eco-friendly technologies for the remediation of arsenic-contaminated soils and water has stimulated interest in arsenic-resistant organisms. For these purposes, twenty-four different bacterial isolates were isolated from arsenic-contaminated soils and detailed morphological, biochemical, and physiological characterizations were accomplished. Results revealed from the in vitro experiment that fifteen bacterial isolates were negative and nine were positive in gram reaction, while two were showed high IAA production

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