Bioaugmentation as microbiome engineering: a framework for evaluating functional performance, persistence, and safety.

Bioaugmentation is increasingly applied to enhance the degradation of contaminants in environmental and engineered systems, yet its effectiveness is often evaluated using endpoints that do not establish whether the introduced microbial function was expressed, sustained, or responsible for the observed outcome. This review considers bioaugmentation as an approach to microbiome engineering rather than a discrete inoculation step. It outlines an evaluation framework based on three complementary criteria: functional performance, functional persistence, and safety. Emphasis is placed on the microbiological determinants of successful implementation, including pathway completion, expression of terminal transformation steps, functional redundancy, ecological compatibility, and the maintenance of introduced activity under variable environmental conditions. The analysis also examines how inoculum design, delivery, selective pressure, retention, and biomonitoring influence the establishment of degradative functions within complex microbial communities. A central theme is the need to distinguish genuine inoculum-driven effects from outcomes generated by biostimulation, modified mass transfer, or changes in contaminant bioavailability. Available evidence indicates that robust interpretation requires an integrated assessment of substrate-to-product relationships, functional and activity markers, community-level responses, and, where appropriate, indicators of biological effect. Microbiological safety considerations are also reviewed, including selective pressures and resistance-related consequences in systems exposed to biologically active contaminants. Bioaugmentation should therefore be evaluated as a controlled microbiotechnological intervention in which function, persistence, mechanistic attribution, and safety are assessed collectively.