IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

17 th International Congress on Nitrogen Fixation
Fremantle, Western Australia
27 November – 1 December 2011
Title Growth inhibition of Sinorhizobium medicae in the presence of amino acids and the absence
of supplemented calcium is alleviated by a mutation in the low pH inducible gene lpiA.
Author Wan Adnawani Meor Osman 1,2 , Ravi Tiwari 1 , Lambert Brau 1 , Vanessa Melino 1 & Wayne
Reeve 1 .
Poster Board Number 2
1 Centre for Rhizobium Studies, Murdoch University, Murdoch, 6150, Western Australia.
Australia
2 Department of Biological Sciences, Faculty of Sciences and Technology, University
Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, Malaysia.
Sinorhizobium medicae WR101 was identified as a mTn5-GNm induced mutant of WSM419 that expressed acid
inducible GUS activity. Characterisation of the mutation revealed that the promoterless gusA gene in mTn5-GNm
was fused to the low pH inducible gene lpiA. The LpiA protein contains a COG0392 signature (indicative of an
integral membrane protein) domain revealing that this protein is most likely a transmembrane protein. In addition,
LpiA also contains three other domains of unknown function including DUF470, DUF471 and DUF472 which
share 83%, 62% and 58% similarity to proteins found in animal pathogens, plant pathogens and other symbionts,
respectively (Reeve et al., 2006). An in depth characterisation of the phenotype of the mutant cells revealed that
the lpiA mutation disrupted the acid-tolerance response (ATR) associated with S. medicae WSM419. In addition
to this, we have now found that the lpiA mutation enables the mutant to grow on amino acid rich media devoid of
calcium. In contrast, the wild-type strain WSM419 cannot grow in this condition and requires calcium to
overcome the growth inhibition found with amino acid containing rich media. Complementation analysis has
revealed that mutant growth can be severely inhibited on media containing amino acids in the absence of
sufficient calcium. These observations have demonstrated that the absence of LpiA is essential for growth on
calcium deficient media containing amino acids. Potential reasons for the growth inhibition of S. medicae by
amino acids in the absence of calcium will be presented.
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2011