Generalized P colonies with passive environment

We study two variants of P colonies with initial content of P colony and so-called passive environment: P colonies with two objects inside each agent that can only consume or generate objects, and P colonies with one object inside each agent using rewriting and communication rules. We show that the first kind of P colonies with one consumer agent and one sender agent can generate all sets of natural numbers computed by register machines, and hence they are computationally complete in the Turing sense. Similarly, also the second kind of systems with three agents with rewriting/communication rules is computationally complete. The paper improves previously published universality results concerning generalized P colonies, and it also extends the knowledge about very simple multi-agent systems capable of universal computation.