Generating Languages by P Systems with Minimal Symport/Antiport

It is known that P systems with two membranes and minimal symport/antiport rules are “almost” computationally complete as generators of number or vector sets. Interpreting the result of the computation as the sequence of terminal symbols sent to the environment, we show that P systems with two membranes and symport rules of weight two or symport/antiport rules of weight one generate all recursively enumerable languages.