The biodesulfurization of sulfide wastewater for elemental sulfur recovery by isolated Halothiobacillus neapoli-tanus in an internal airlift loop reactor (IALR) was investigated. The flocculant producer Pseudomonas sp. strain N1-2 was used to deposit the produced elemental sulfur during biodesulfurization. The functional group analysis indicated that biofloculation was closely associated with N-H and C=O. The biodesulfurization system performed well under moderate water quality fluctuations (1.29-3.88 kgm(-3).d(-1) COD; 1.54-3.08 kgm(-3).d(-1).S2-) as it maintained stable S2- removal and sulfur flocculation rates. Meanwhile, the qRT-PCR analysis indicated that the transcriptional level of cbbL decreased in the presence of organic carbon, while the expressions of sqr, sat, and cytochrome C3 increased under higher sulfide stress. Moreover, the relative proportions of Halothiobacillus was strengthened via microbial intervention of the LJN1-3 strain. The S2- removal efficiency and elemental sulfur production was further improved by 32.5% and 28.2%, respectively, in an IALR.