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Aerobic Heterotrophic Bacteria and Azospirillum in Certain Saline Soils of Bangladesh

M. Motiur Rahman
Department of Botany, Jahangimagar University, Savar, Dhaka, Bangladesh

S. Mubassara
Department of Botany, Jahangimagar University, Savar, Dhaka, Bangladesh

S. Hoque
Department of Soil, Water and Environment, University of Dhaka, Bangladesh

Zahed U. M. Khan
Department of Botany, Jahangimagar University, Savar, Dhaka, Bangladesh

Abstract/ Executive Summary:

The population of aerobic heterotrophic bacteria and microaerophilic di azotroph Azospirillum occurring in the saline habitat of a saline prone zone of Satkhira district, Bangladesh was studied. These organisms were found to occur in the saline non-rhizosphere soil, and also in the root and rhizosphere soil of Cynodon dactylon. The total aerobic heterotrophic bacteria in root samples in control medium (nutrient agar) varied from 31.2x I a⁰ to 67 .2x 1 a⁰ cfu/g but in saline medium (nutrient agar with 3% additional NaCI) the population was less ranging from 17.3xla⁶ to 58.6xla⁶ cfu/g. Highest number of bacteria was found in the root samples and the least in non-rhizosphere soil samples. In case of all samples the Azospirillum population ranged from a.1 xl a⁶ to 24.6xl a⁶ MPN/g dry wt, and a.1 x I a⁶ to 14.4xla⁶ MPN/g dry wt. in saline medium (semi-solid Nfb+3% NaCl) and normal medium (semi-solid Nfb without extra NaCl) respectively. Root samples harboured highest population of Azospirillum and non-rhizosphere soil samples showed the least.

Keywords: Heterotrophic bacteria, Azospirillum, Saline soils

Location: Saline area in the district Satkhira

Start Date: 00-00-2006

End Date: 00-00-2006

Program Area: Crop-Soil-Water Management

Commodity: Bio fertilizer

Objectives:

1. The present work was undertaken to study the natural status of the population of Azospirillum in some saline soils of the district Satkhira, Bangladesh.

Methodology:

The samples of non-rhizosphere soil, soil of rhizosphere of Cynodon dactylon and the roots of the same plant were collected from five different locations of saline area in the district Satkhira. The pH values of soil and root samples were determined on aqueous soil suspensions (1:2.5 soil to water ratio) and thick root suspensions (fresh tissues were ground with mortar and pestle) using an electric pH meter. Electrical conductivity (EC) of the soil was determined from saturation extract with appropriate dilution, wherever necessary. The root samples were processed as described by Watanabe and Brotonegoro (1981). The roots were thoroughly washed for several times with sterile distilled water. The clean root samples were macerated in sterile mortars and sterile water was added to each macerated sample to prepare suspension (1:10). Suspension (1: 10) of each soil sample was prepared by mixing soil with sterile water. The population of aerobic heterotrophic bacteria in the samples was determined by dilution plate count method using nutrient agar (control medium) and nutrient agar containing 3% extra NaCI (saline medium). The population of Azospirillum in root samples and soil samples were estimated by the most probable number (MPN) method. Serial dilutions from 10-1 to 10-7 of the suspension of each root sample and soil sample were prepared. Each of 5 tubes containing 7 ml sterile medium was inoculated with 0.1 ml of particular dilution. In this way the dilutions from 10-3 to 10-6 were used for the inoculation of medium in the tubes. Two sets of tubes were thus inoculated; one set contained Nfb semisolid medium (control medium) and the other set contained the same medium with which 3% extra NaCI was added (saline medium). The inoculated tubes were incubated at 35°C for 72 hours. The appearance of a thin, dense white, pellicle a few mm below the surface of the medium showed the presence of Azospirillum in the tubes. The pellicles were examined under microscope for the presence of gram negative, vibroid and actively motile cells. From the number of' positive tubes inoculated by higher dilutions of sample the most probable number (MPN) of Azasplrillum was determined.

Source of Information: Bangladesh J. Life Sci. 18(1): 105-110, 2006 (June)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The total aerobic heterotrophic bacteria in root samples in control medium (nutrient agar) varied from 31.2x I a⁰ to 67 .2x 1 a⁰ cfu/g but in saline medium (nutrient agar with 3% additional NaCI) the population was less ranging from 17.3xla⁶ to 58.6xla⁶ cfu/g. Highest number of bacteria was found in the root samples and the least in non-rhizosphere soil samples. In case of all samples the Azospirillum population ranged from a.1 xl a⁶ to 24.6xl a⁶ MPN/g dry wt, and a.1 x I a⁶ to 14.4xla⁶ MPN/g dry wt. in saline medium (semi-solid Nfb+3% NaCl) and normal medium (semi-solid Nfb without extra NaCl) respectively. Root samples harboured highest population of Azospirillum and non-rhizosphere soil samples showed the least.

Knowledge Management: Journal