Determination of desirable properties of bacteria, fungi and their biofilm associated with rubber rhizosphere

R P Hettiarachchi,A Thewarapperuma,T Gunathilake,R S Dharmakeerthi,A N Jayakody,G Seneviratne,K E De Silva

doi:10.4038/tar.v27i4.8216

Abstract

Rhizosphere microbes and their community structure ‘biofilm’ play a significant role in maintaining the dynamic of soil fertility. In this study, isolated bacteria and fungi from rubber root rhizosphere in red yellow podzolic soils and their biofilm structures were formulated under laboratory conditions. They were evaluated for their effectiveness on solubilization of insoluble inorganic compounds, calcium hydrogen phosphate (CaHPO4), higher grade Eppawala rock phosphate (HERP) and Eppawala rock phosphate (ERP)) in liquid medium, production of indole acetic acids (IAA) and capacity of fixing atmospheric nitrogen using acetylene reduction assay (ARA). The relationships between variables were identified using regression analysis. The solubilization of CaHPO4 in liquid medium by different bacterial strains was accompanied by a drop in pH (4.2-6.1) from an initial pH of 6.8-7.0, which followed a polynomial relationship between the pH of the medium and the amount of soluble phosphorus. The medium with HERP showed less relationship compared to CaHPO4 between the above parameters. No correlation was found between pH and the amount of P solubilized of the culture medium containing ERP. Out of 30 bacterial isolates, five isolates formed proper biofilm community structure. The biofilm solubilized significantly high amount of phosphorus in liquid medium containing CaHPO4 compared to their bacterial and fungal counterparts and was observed synergistic effect for ARA. Production of IAA of biofilm was higher than that of bacteria alone cultures. Thus the biofilm formation of rhizosphere microbes seems to be very important for improved soil fertility.

Highlights

Rubber plantations were first established in Sri Lanka at the beginning of the 20th century
The isolates which were able to solubilize phosphorus less than 100ppm were clustered separate to others (Figure 2). Bacterial isolates those have an ability to solubilize phosphorus more than 100ppm of the medium with CaHPO4 were further evaluated for their phosphorus solubilization of the medium with HERP and ERP
Strains B5, B6, B17, B23 and B25 exhibited higher solubilizing capability for the three sparingly soluble inorganic phosphates in liquid medium than the other strains and it was evidenced by the clustering pattern of the dendrogram based on phosphorus solubilization in the medium with CaHPO4 (Figure 2)

Summary

Introduction

Rubber plantations were first established in Sri Lanka at the beginning of the 20th century. Some soil bacteria that are able to colonize surrounding the plant roots is called rhizobacteria, and play a significant role in maintaining the dynamic of soil fertility and plant growth (Kloepper, 2003; Bakker et al, 2007). Rhizobacteria which provides beneficial effects on the host plant growth via direct and indirect mechanisms, are referred to as plant growth promoting bacteria (PGPB) (Kloepper and Schrot, 1981). These bacteria support fixation of atmospheric nitrogen, solubilization of phosphatic minerals and secretion of stimulating hormones, like auxin known as Indole 3 Acetic Acid (IAA) (Huddedar et al, 2002; Chopade et al, 2008; Bashan and de-Bashan, 2010). Some soil bacterial isolates have an ability to solubilize inorganic low soluble phosphates (Illmer et al, 1995; Wakelin et al, 2004; Chen et al, 2006; Song et al, 2008)

Objectives

Methods

Results

Conclusion