Bio-digital systems that merge microbial life with technology promise new modes of computation, combining biological adaptability with digital precision. Yet realizing this potential symbiotically -- where biological and digital agents co-adapt and co-process -- remains elusive, largely due to the absence of a shared vocabulary bridging biology and computing. Consequently, microbes are often constrained to uni-directional roles, functioning as sensors or actuators rather than as active, computational partners in bio-digital systems. In response, we propose a taxonomy and pathways that articulate and expand the roles of biological and digital entities for synergetic bio-digital computation. Using this taxonomy, we analysed 70 systems across HCI, design, and engineering, identifying how biological mechanisms can be mapped onto computational abstractions. We argue that such mappings enable computationally actionable directions that foster richer and reciprocal relationships in bio-digital systems, supporting regenerative ecologies across time and scale while inspiring new paradigms for computation in HCI.
ACM CHI Conference on Human Factors in Computing Systems