Quorum sensing in bacteria of rice rhizospheres from Chhattisgarh, India

Abstract

Quorum sensing is a phenomena used by bacteria for regulation of some important characteristics coordinately. Gram-negative and Gram-positive bacteria, both utilize this system of communication, but they use different signal molecules for this, i.e. Gram-negative bacteria preferentially use acyl homoserine lactone (AHL). Rhizospheric soil is rich in bacterial diversity, with the presence of both types of bacteria. It will be useful if we know the quorum sensing based communications among bacteria present in rhizospheric soil. This work was undertaken with the idea to explore the diversity of AHL producing bacteria in soil. For this, bacteria were isolated from rice rhizosphere from field located in Dhamtari district of Chhattisgarh. To study quorum sensing, detection of AHL production was performed by colorimetry method. Out of total 29 bacterial isolates, only three Gram-negative bacteria showed positive result for AHLs production. These 3 isolates were selected for further study. The isolates were characterized by biochemical test. Other characteristics of these bacteria were also tested, like antibiotic resistance profile, indole test, and capability to biofilm formation, phosphate solubilization as well as their growth in different specific culture media. The Results suggest that AHLs producing bacteria may belong to family of Pseudomonas sp., which are reported in different researches to be part of the PGPR group of organisms. This work forms the base to study the cell-cell communication in plant rhizospheres.

Keywords: AHL). Rhizospheric; Quorum sensing; bacteria.

Figure 1

Representative pictures of microscopic observation. Gram-Positive Bacteria- A (SA7) and B (SA11), Gram-negative Bacteria- C (SA3) and D (SA6)

Figure 2

Colorimetry results. Positive results of SA4, SA6, SA16 (dark brown color), C-Control

Figure 3

Selected isolates SA4, SA6 and SA16 grown in different media. MacConkey agar (A), Pikovskaya's agar (B), King's B medium (C), King's B medium under UV light (D) and Congo red agar (E. a-E. c).

Figure 4

Antibiotic disk diffusion assay. SA4 (A), SA6 (B) and SA16 and (C) details of the antibiotic disks are given in text.

Figure 5

Biochemical and other test. Glucose fermentation test (A), Oxidase test (streaked as plus sign) (B), Lactose fermentation test (C), Gelatin hydrolysis test (D), Indole test (E) and Urease test (F). C- Control, PC- Positive control.