Biofilm‐Controlled Molecular Crosstalk: Nitrogen Fixation, Arsenic Transformation and Antibiotic Resistance

Biological nitrogen fixation, arsenic biotransformation and antibiotic resistance are conventionally studied separately, yet the environmental biofilm—bacteria′s dominant organisational state in soils, sediments and rhizospheres—supplies a shared physicochemical and genetic context in which the three can intersect. The extracellular polymeric substance (EPS) matrix imposes steep oxygen, redox and metabolite gradients across micrometre scales and demonstrably shelters oxygen‐sensitive nitrogenase, retains arsenic‐transforming enzymes (ArsC, ArsM and AioA) and elevates horizontal gene transfer (HGT) frequencies orders of magnitude above planktonic conditions. Individual circuits are genetically established in single organisms—RpoN coactivates pslA and nifA and the non‐coding RNA NfiS stabilises nifK and katB transcripts, in Pseudomonas stutzeri A1501—but their assembly into one programme linking surface commitment, diazotrophic activation and oxidative stress defence, with additional c‐di‐GMP and ArsR stimulon input under arsenic stress, is proposed, not demonstrated. Arsenic‐driven coselection of antibiotic resistance genes (ARGs) is the best‐supported limb, operating through cross‐resistance (RND efflux), co‐resistance (ars–ARG colocation on Tn21, Class 1 integrons, IncP/IncQ plasmids) and coregulation (ArsR stimulon, SOS‐derepressed intI1), whereas the proposal that diazotrophy‐derived ammonium supports S‐adenosyl‐l‐methionine supply for ArsM‐mediated methylation rests on gene coenrichment and rate correlation rather than direct flux measurement. This review integrates these processes into a single biofilm framework, classifies each proposed linkage by the evidence behind it, identifies candidate trifunctional mobile elements carrying ars, nif and ARG cassettes in hyperaccumulator rhizospheres and paddy soils and specifies the minimum spatially resolved single‐cell dataset (bacterial‐MERFISH, par‐seqFISH and SIP‐NanoSIMS) needed to test the proposed couplings.