SCREENING OF ORGANIC ACID PRODUCTION POTENTIALITY OF A RICE RHIZOSPHERIC PURPLE NON SULFUR BACTERIUM RUBRIVIVAX GELATINOSUS STRAIN RASN4

Abstract

Organic acids are long chained organic carbon compounds with their attached functional 
carboxylic groups showing acidic properties, produced exogenously by a number of 
microorganisms including plant growth promoting rhizobacteria (PGPR) showing along with 
their other PGPR potential traits. This characteristics can be exploited as a potentially significant 
quality for promoting of plant growth, development and vigor with substantial enhancement of 
crop productivity and yield by facilitating microbial biomineralization of various insoluble 
inorganic macro and micro trace metal elements that are essential for plants, by converting them 
into their solubilised plant available forms in order to facilitate plant growth and development. 
So, such potentiality of exogenous organic acid bio production could be of an another 
advantageous capability for PGPRs which has its additional synergistic significance along with 
the other common traditional PGPR traits of PGPR microorganisms in order to bioformulate a 
potential microbial biofertilizer for agricultural crop fields.
For this said purpose, the isolated Purple non sulfur bacterium (PNSB) Rubrivivax gelatinosus
strain (RASN4) was first screened qualitatively in terms of their comparative Rf values with 
reference control of known specific organic acids using as control on paper chromatography 
followed by their determination of acid unitage (AU) values. The Rf values obtained from the 
bacterial culture supernatant of isolated RASN4 strain on paper chromatography were found as 
0.66, 0.92, 1.03, 0.12, 0.23, and 0.34 respectively that were compared with their specific 
reference control of known specific organic acids, and found to be coincided with citric (0.72), 
fumaric (0.98), succinic (1.08), acetic (0.17), propionic (0.27) and butyric (0.37) respectively. 
This has become further evident from the determination of acid unitage (AU) values of the 
isolated strain RASN4 culture supernatant with the highest value of 3.11 (4th replicate) and 
lowest values of 2.88 (5th replicate) with an average (AU) value of 2.96. So after obtaining the 
results from the both end followed by their comparing ,it can be postulated that the rice 
rhizospheric PNSB bacterium Rubrivivax gelaponosus (RSN4) has the significant potentiality for 
showing promising performance for microbial organic acids exoproduction along with its other traditional PGPR traits.This is also the first time report of organic acid exoproduction by PNSB 
bacterial strain Rubrivivax gelatinosus (RSN4) as became evident through qualitative screening 
of the present study that can be exploided to bioformulate a potential microbial bio fertilizer for 
the benefit of agriculture and mankind .