SLC5A5 and goiter: In goiter rats, 16S rRNA sequencing revealed eight differentially abundant microbial taxa including significantly reduced B. bifidum, accompanied by: (1) impairment of two butyrate synthesis pathways, (2) decreased levels of six SCFAs (including butyrate), (3) impaired thyroid iodine uptake, (4) downregulated NIS expression, and (5) thyroid dysfunction [reduced triiodothyronine (T3), thyroxine (T4), free T3 (FT3), free T4 (FT4) with elevated thyroid-stimulating hormone (TSH)] - all measurements showing statistical significance (p < 0.05).