Functional activity of E. coli RNase R in the Antarctic Pseudomonas syringae Lz4W

Background

In Antarctic P. syringae RNase R play an essential role in the processing of 16S and 5S rRNA, thereby playing an important role in cold-adapted growth of the bacterium. This study is focused on deciphering the in vivo functional activity of mesophilic exoribonuclease R and its catalytic domain (RNB) in an evolutionary distant psychrophilic bacterium Pseudomonas syringae Lz4W.

Results

Our results confirm that E. coli RNase R complemented the physiological functions of the psychrophilic bacterium P. syringae RNase R and rescued the cold-sensitive phenotype of Pseudomonas syringae ∆rnr mutant. More importantly, the catalytic domain (RNB) of the E. coli RNase R is also capable of alleviating the cold-sensitive growth defects of ∆rnr mutant as seen with the catalytic domain (RNB) of the P. syringae enzyme. The Catalytic domain of E. coli RNase R was less efficient than the Catalytic domain of P. syringae RNase R in rescuing the cold-sensitive growth of ∆rnr mutant at 4°C, as the ∆rnr expressing the RNB^Ec (catalytic domain of E. coli RNase R) displayed longer lag phase than the RNB^Ps (Catalytic domain of P. syringae RNase R) complemented ∆rnr mutant at 4°C. Altogether it appears that the E. coli RNase R and P. syringae RNase R are functionally exchangeable for the growth requirements of P. syringae at low temperature (4°C). Our results also confirm that in P. syringae the requirement of RNase R for supporting the growth at 4°C is independent of the degradosomal complex.

Conclusion

E. coli RNase R (RNase R^Ec) rescues the cold-sensitive phenotype of the P. syringae Δrnr mutant. Similarly, the catalytic domain of E. coli RNase R (RNB^Ec) is also capable of supporting the growth of Δrnr mutant at low temperatures. These findings have a vast scope in the design and development of low-temperature-based expression systems.