Production of molybdenum blue by two novel molybdate-reducing bacteria belonging to the genus Raoultella isolated from Egypt and Iraq

Abstract

Aim: The aim of this study was to isolate potential molybdate-reducing bacteria to be used for bioremediation.

Methods and results: Two molybdate-reducing bacteria (Mo1 and MoI) were isolated from polluted soil samples from Ismailia Canal, Egypt and Sallah Elddin Governorate, Iraq respectively. The isolates exhibited dark blue colonies when grown on solid medium containing sodium molybdate which indicated the reduction of molybdate to molybdenum (Mo) blue. The absorbance values at 865 nm were 0·743 ± 0·007 and 0·453 ± 0·005 for Mo1 and MoI respectively. The Mo blue produced showed characteristic absorption spectrum peak at 865 nm and a shoulder at 700 nm. The isolates were identified by 16S rRNA genes sequencing and were submitted to GenBank as Raoultella ornithinolytica strain Mo1 and Raoultella planticola strain MoI. The optimum conditions were glucose as electron donor, initial pH of 6 and incubation temperature of 30°C. Scanning electron micrographs were taken for both isolates in the presence and absence of molybdate source.

Conclusion: To the best of our knowledge, this is the first recordation of molybdate reduction by Raoultella sp. isolated from Egypt and Iraq.

Significance and impact of the study: The isolated bacteria belonging to the Raoultella could be used in in situ bioremediation.

Keywords: Raoultella ornithinolytica; Raoultella planticola; molybdate; molybdenum blue; reduction.