Development of exobiopolymer-based biosensor for detection of phosphate in water

The present study was conducted to develop a biosensor by exploiting phosphate-binding capacity of exobiopolymer (EBP) produced by Acinetobacter sp. An environmental isolate of EBP-producing Acinetobacter sp. was subjected to transposon (Tn5) mutagenesis to overproduce EBP and afford improved phosphate selectivity. A mutant producing the highest amount of EBP with high phosphate-binding capacity was selected for biosensor probe fabrication. Phosphate samples were filtered through EBP-coated membranes and phosphate retained on membranes was determined by molybdenum blue method. The color produced was read using a LED 690 nm/photodiode detection system linked to an amplifier and signals were converted to appropriate phosphate concentrations. The biosensor had a limit of detection of 0.5 mg/L and a limit of quantification 1 mg/L. The biosensor as well as the probe were found to be stable for at least 28 days. In conclusion, we believe that the biosensor may have applications in monitoring of wastewater and environmental samples. Further, the enrichment of phosphate levels by EBP can help in analysis of very low phosphate concentrations.

Analysis of the genetic region encoding a novel rhizobiocin fromRhizobium leguminosarumbv.viciaestrain 306

Cross-testing of a number of strains of Rhizobium leguminosarum for bacteriocin production revealed that strain 306 produced at least two distinct bacteriocins. Further analysis involving plasmid transfer to Agrobacterium and other hosts demonstrated that there were bacteriocin determinants on plasmids pRle306b and pRle306c, as well as a third bacteriocin. The bacteriocin encoded by pRle306b was indistinguishable from the bacteriocin encoded by strain 248, whereas the bacteriocin encoded by plasmid pRle306c had a distinctive spectrum of activity against susceptible strains, as well as different physical properties from other bacteriocins that we have studied in our lab. Two mutants altered in production of the pRle306c bacteriocin were generated by transposon Tn5 mutagenesis, and the DNA flanking the transposon inserts in these mutants was cloned and characterized. DNA sequence analysis suggested that the pRle306c bacteriocin was a large protein belonging to the RTX family, and that a type I secretion system involving an ABC type transporter was required for export of the bacteriocin. A mutant unable to produce this bacteriocin was unaltered in its competitive properties, both in broth and in nodulation assays, suggesting that the bacteriocin may not play a major role in determining the ecological success of this strain.Key words: Rhizobium, bacteriocins, RTX proteins, plasmids.