TANGGAPAN FISIOLOGIS RHIZOBAKTERI TERHADAP CEKAMAN OSMOTIK DAN KEASAMAN

Under environmental stress, rhizobacteria will give physiological response through changes of metabolism by synthesising some specific proteins and metabolites. This study aims at understanding physiological responses of rhizobacteria to osmotic and acidity stress. The study was conducted in three parts, i.e. (a) selection and identification of rhizobacteria tolerant to osmotic and acidity stress using phenotypic and molecular analysis of 16S rDNA, (b) analysis of specific intracellular, membrane and extracellular protein profiles by slab gel SDS-PAGE 12% and (c) analysis polar and non-polar metabolite profiles by using GC / MS RXi-5ms. The results showed that IMRG-19 isolate demonstrate higher tolerance to osmotic and acidity stress than the other isolates (IMRG-5 and IMRG-30). Based on phenotypic and molecular characterization, IMRG-19 was confirmed as Klebsiella pneumoniae with a confidence level of 97-99%. Analysis demonstrated that several intracellular, membrane, or extracellular proteins were synthesised under specific stress condition. Under osmotic stress, an intracellular protein of 42.7 kDa, and a membrane protein of 53.3 kDa were synthesised. Acid stress, on the other hand, resulted in the synthesis of intracellular proteins of 54.7 kDa, 25.3 kDa, and 14.2 kDa, and a 43.9 kDa membrane protein, and extracellular proteins of 17 � 29 kDa. Under osmotic and acidity stress condition, a specific intracellular protein of 26.7 kDa and a membrane protein of 61.1 kDa were detected. Analysis of polar and non-polar metabolite synthesis pattern, demonstrated that some specific metabolites were synthesized under osmotic and acidity stress in the form of fatty acids (palmitic acid, oleic acid and stearic acid), amide compounds (octanamide, dodecanamide and hexanamide) and phenolic compounds (octanol and phenol). Metabolites may have a double role either as osmoprotectant and as chelating agents for aluminum ions (Al3+). Under Al2(SO4)3 stress it was also observed that silicate anion tetramer and silicone polymer were synthesised. The two metabolites effectively binds Al3+. In addition, there is a correlation between proteins and metabolites. It was also observed that specific proteins related with the synthesis of specific metabolites responsible for tolerance to osmotic and acidity stress were also synthesised. Those proteins are 13,9 kDa and 46,1 kDa relating to synthesis of fatty acid, 30,1 kDa relating to synthesis of amide and 85,5 kDa for synthesis of phenolic compoun