Isolation and molecular identification of salt tolerant probiotic bacteria and their impacts on rice (Oryza sativa) seedlings

Abstract

Soil salinity is a serious problem in the coastal areas of Bangladesh. It is the main barrier to attain sustainability in crop production in those particular areas. Moreover, the situation is getting worse along with time. Therefore, an eco-friendly and sustainable approach is required to overcome this problem. Discovery of plant growth promoting bacteria (PGPB) and their application to crop plants are considered as promising and effective biotechnological approaches to fight against salt-stress to crop plants. The objectives of this study were to isolate and characterize salt tolerant PGPB from the rice plants cultivated in saline soils and evaluate their performances on seed germination and seedling growth of rice. The study was performed at the laboratories of the Institution of Biotechnology and Genetic Engineering (IBGE) in Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU). Rice plant samples were collected from salt-affected areas in Chattogram, Noakhali, Lakshmipur and Cox’s Bazar districts. Forty one salinity tolerant bacteria were isolated and characterized for screening in vitro for both salinity tolerance, and three highly salt tolerant isolates were further evaluated on seed germination and seedling growth of rice cv. BRRI dhan 29 (salinity susceptible) and BINA dhan 10 (salinity tolerant). Priming of rice seeds with three highly salt tolerant (up to 12% NaCl w/v) isolate viz. BTCoSo2, BTCoR2 and IBGE3C promoting growth of rice seedling and the effects were pronounced in BINA dhan 10. Among the three bacteria, IBGE3C displayed best performances on seedling growth of rice under varying salinity was sequenced and the strain exhibited 100% 16S ribosomal RNA gene sequence homology with Brevibacterium sediminis IBGE3C (accession no. MZ573246) strain. Brevibacterium sediminis is a potential plant growth promoting bacteria and it can significantly increase the shoot and root length in plants. Also, the isolation of B. sediminis from sea water and deep-sea sediments has been previously reported v which suggests it as a potential salt tolerant bacteria. Brevibacterium spp. are rod- shaped, non-spore forming gram-positive bacteria. This study for the first time identified B. sediminis strain IBGE3C (accession no. MZ573246) as a salt tolerant PGPB from the rice cultivated in Lakshmipur district of Bangladesh. In addition, the collected rice variety was BRRI dhan 28 which is also a widely cultivated variety throughout the country. However, the bacteria has been isolated from plant’s root sample which is required for further study for its practical application in the enhancement rice production in the saline soils in Southern districts of Bangladesh.