Uses inorganic polyphosphate (polyP) as a donor to convert GDP to GTP. [phosphate](n) + GTP = [phosphate](n+1) + GDP Expression increases during the exponential phase of growth and remains at a steady level up to the stationary phase. Knockout mutant is more susceptible to acid, heat and hypoxic stress. Mutant has reduced GTP levels. Belongs to the polyphosphate kinase 2 (PPK2) family. Class I subfamily.