Catalyzes the formation of acetyl phosphate from acetate and ATP. Can also catalyze the reverse reaction. During anaerobic growth of the organism, this enzyme is also involved in the synthesis of most of the ATP formed catabolically. The main pathway for acetate production during exponential phase (PubMed:16080684). acetate + ATP = acetyl phosphate + ADP Mg(2+). Can also accept Mn(2+). Metabolic intermediate biosynthesis; acetyl-CoA biosynthesis; acetyl-CoA from acetate: step 1/2. Homodimer. Expressed during exponential phase, decreases as cells enter stationary phase at pH 7.0. Expression is inhibited at pH 6.0. Part of the ackA-pta operon. Not essential it can be deleted. Belongs to the acetokinase family.