Brazil, D.

Culhane, J.

Dowling, D.

Germaine, K.

Otieno, N.A.

Ryan, D.

English

Wageningen UR (University & Research Centre): Publication System

Phosphate solubilisation and gluconic acid production by endophytic 
bacterial strains and ability to promote plant growth in oil seed rape 
(Brassica napus) 
Otieno NA1, Culhane J2, Germaine K3, Brazil D4, Ryan D5, Dowling D6 
1Postgraduate student, Department of Health and Science, Institute of Technology Carlow Ireland 
2Postgraduate student, Department of Health and Science, Institute of Technology Carlow Ireland 
3Postdoctoral research scientist, Department of Health and Science, Institute of Technology Carlow, Ireland 
4Senior Lecturer, Department of Health and Science, Institute of Technology Carlow, Ireland 
5Chairman of Department of Health and Science, Institute of Technology Carlow, Ireland 
6Head of School of Science, Institute of Technology Carlow, Ireland 
 
ABSTRACT 
Phosphate solubilising bacteria (PSB) are able to convert insoluble phosphate into soluble forms and have been 
used to enhance the solubilisation of otherwise insoluble soil phosphate for plant growth promotion. Several 
studies have shown that the release of low molecular weight organic acids is a major mechanism for solubilising 
insoluble phosphate. In this study the production of gluconic acid during inorganic phosphate solubilisation in 
conjunction with liberation of soluble phosphate and the influence on plant growth as a function of phosphate 
solubilisation by endophytic strains was analysed. Solubilisation of Ca3(PO4)2 in National Botanical Research 
Institute’s Phosphate (NBRIP) growth medium varied among the endophytes  with strain L132 recording the 
highest P-liberated (1109.33 µg/ml) followed by L228 (Pseudomonas sp) (912.00 µg/ml) while Escharachia 
coli JM109 used as a negative control had below detection limit. In all cases, the final supernatant had a 
significant pH decrease with L228 recording the highest decrease, 2.74 units (6.08 – 4.06 pH) compared to 
M109 that had 0.75 units (6.08 – 6.05 pH). High Performance Liquid Chromatography (HPLC) analysis of the 
culture filtrate to quantify gluconic acid produced by the strains showed that L321 (Pseudomonas sp) produced 
the highes gluconic acid level (33.21±2.34 mg/ml) followed by L132 (31.46±3.71 mg/ml) and these were 
significantly different from the rest of the strains. The results suggest that acidification was the main strategy for 
solubilising phosphate. In this study, a clear relationship was observed between supernatant acidification and P 
solubilisation from Ca3(PO4)2. However, no significant difference was observed for key growth parameters in oil 
seed rape (OSR) between PSB treatments and uninoculated control treatments. More research is needed to 
investigate the performance and use phosphate solubilising bacteria as bacterial inoculants particularly in field 
experiments. The result of this study indicates in planta expression of P solubilisation traits may be more 
complex than those in vitro studies. Thus future research should investigate the stability and performance of the 
phosphate solubilising traits once the bacteria has been inoculated. 
 
Keywords: Phosphate solubilisation, gluconic acid production, promote plant growth, endophytic bacterial 
strains, oil seed rape 


Phosphate solubilisation and gluconic acid production by endophytic bacterial strains and ability to promote plant growth in oil seed rape (Brassica napus)

https://library.wur.nl/ojs/index.php/AE2012/article/download/12440/11942

Phosphate solubilisation and gluconic acid production by endophytic bacterial strains and ability to promote plant growth in oil seed rape (Brassica napus)

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