A new uranium bioremediation approach using radio-tolerant Deinococcus radiodurans biofilm

Deinococcus radiodurans is the most radiation-tolerant organism ever known. It has gained importance in recent years as apotential candidate for bioremediation of heavy metals, especially the radioactive type. This study investigates the efficiency of a recombinant D. radiodurans (DR1-bf?) strain with an ability to form biofilm for uranium remediation. Themodified Arsenazo III dye method was used to estimate the uranium concentration. Uranyl nitrate aqueous solution wasgenerated during the operation of nuclear fuel reprocessing. The D. radiodurans biofilm (DR1-bf?) grown in the presenceof 20 mM Ca2? showed remarkable ability of uranyl ion removal. DR1-bf? (?Ca2?) biofilm removed *75±2% of1000 mg/L uranium within 30 min post-treatment from uranyl nitrate aqueous solution. Uranium removal rate was alsofound to be directly proportional to biofilm age. This study discusses the ability of D. radiodurans biofilm in uraniumremoval.

Microbiota of spent nuclear fuel pool water with emphasis on their biofilm forming ability on stainless steel (SS-304L)

Spent nuclear fuel (SNF) pool is an essential unit of a nuclear power plant infrastructure, where radioactive fuel rods arekept for cooling and shielding, before reprocessing. This study explored the presence of bacteria in SNF pool water withemphasis on their capability to form biofilms on pool wall cladding material stainless steel (SS-304L). Bacteria wereisolated from SNF pool water and were characterized using 16S rRNA gene sequencing. The six bacterial isolates (Bacillussubtilis, Staphylococcus sps., S. arlettae, S. epidermidis, S. auricularis and Chryseobacterium gleum) can grow and formbiofilms at very low nutrient condition as well as in chronic radioactivity. The bacterial isolates formed biofilm on SS-304Land glass. However, the biofilm parameters assessed by CLSM microscopy showed that the strains preferred SS-304Lsurface for biofilm formation. On SS-304L, the maximum biomass (0.45 lm3/lm2) was formed by S. arlettae whencompared to maximum biomass (0.054 lm3/lm2) by Staphylococcus sp., on glass. Maximum biofilm thickness on SS304L was observed by Staphylococcus sp. (8.81 lm) when compared to that of S. epidermidis (4.16 lm) on the glasssurface. The biofilm formation on SS-304L surface suggests the possible risk of microbial-induced corrosion of SNF poolcladding material. This study highlights the need for mandatory monitoring of microbial biofilm formation in an extremeenvironment such as SNF pool.

Temperature effect on behaviour, oxygen consumption, ammonia excretion and tolerance limit of the post larvae of shrimp Penaeus indicus.

The present study has been carried out to know the effect of temperature on behaviour, equilibrium loss and tolerance limit of the post larvae of shrimp Penaeus indicus. The experimental temperatures were selected based on the thermal tolerance limit. The experiments were conducted at a specific temperature for duration of 48 hr. The thermal tolerance experiments were conducted in two ways: in direct exposure and in gradually increasing temperature. The upper and lower lethal temperatures for the post larvae of shrimp P. indicus were 43.5 degrees C and 8 degrees C respectively. During tolerance experiment, no mortality was observed at 33 degrees C and 35 degrees C. But at 38 degrees C with gradual increase in temperature, 30% loss of equilibrium and mortality were recorded in 24.31 hrs and 25.07 hrs, and the remaining 70% were alive. On the contrary, when the post larvae of shrimps were directly exposed to 38 degrees C, almost 80% loss of equilibrium and mortality were recorded in 30.22 hrs and 30.40 hrs, remaining 20% were alive. At 40 degrees C with gradual increase in temperature, 100% loss of equilibrium and mortality were recorded in 25.32 hrs and 25.56 hrs. On the other hand, when the post larvae of shrimps were directly exposed to 40 degrees C, 100% loss of equilibrium was observed in 0.37 hrs and mortality in 1.40 hrs. These behavioral responses include an elevated temperature of 12 degrees C, surfacing, dashing against glass wall, jumping out of the water, etc. In general, the rate of oxygen consumption and ammonia excretion was found to enhance with increasing temperature. In the present study, it was found that gradual increase in temperature favours the shellfish population to escape from the thermal exposure as compared to direct exposure.