Sulfur is the fourth most prevalent essential macronutrient, which is vital for all organisms, including humans, animals, plants, and microorganisms (Chaudhary et al., 2023). Constituting approximately 0.05–0.1 % of the Earth's crust by weight, sulfur plays an important role in biological systems. In soil environments, sulfate typically accounts for only 1–5 % of the total bioavailable sulfur, while organic sulfur compounds such as sulfonates and sulfate esters make up more than 95 % of the sulfur content (Wu et al., 2021). In bacterial cells, sulfur constitutes 0.5–1 % of the dry cell weight, highlighting its importance in cellular composition and function (Hou et al., 2023), as a fundamental component of amino acids (methionine and cysteine), cofactors (e.g., biotin, coenzyme A, thiamine, and lipoic acid), and redox-active molecules (e.g., iron‑sulfur clusters, disulfide bonds, glutathione, and mycothiol) (Wu et al., 2021).

Microbial metabolism and biotransformation of organic sulfur compounds play an indispensable role in the biogeochemical sulfur cycle (Gupta et al., 2024; Jørgensen et al., 2019; Zhou et al., 2025), which occurs in both terrestrial and aquatic habitats, including interactions between prokaryotes, eukaryotes, and numerous chemical processes (Kümpel et al., 2024). Central to this cycle are sulfate-reducing bacteria, including the genera Desulfovibrio, Desulfobacter, Desulfotomaculum, Thermodesulfovibrio, and Thermodesulfobacterium, which perform dissimilatory sulfate reduction (Bagheri Novair et al., 2024), mediated by enzyme products of the genes sat (sulfate adenylyltransferase), aprAB (adenylylsulfate reductase), and dsrAB (dissimilatory sulfite reductase) (Umezawa et al., 2020). Conversely, sulfur-oxidizing bacteria, including Thiobacillus, Acidithiobacillus, and Beggiatoa, oxidize reduced sulfur compounds to sulfate using the Sox system, which is encoded by the soxTRS-VWXYZABCDEFGH operon (Ranadev et al., 2023). Additionally, heterotrophic bacteria, including Pseudomonas, Rhodococcus, and marine Roseobacter clade members, metabolize organic sulfur compounds such as sulfonates, thiols, and dimethylsulfoniopropionate (DMSP). In sulfate-limited environments, these bacteria recruit specific transporters (SsuABC, TauABC) and catabolic enzymes (DmdA, DddP) for the uptake and degradation of organic sulfur compounds (Curson et al., 2011; Kertesz, 2000). The microbial processes and genetic systems together govern the global sulfur cycle, influencing nutrient dynamics, ecosystem productivity, and the emission of climate-relevant gases.

Millions of megatons of organic sulfur compounds are produced annually by both biological and industrial activities. Prokaryotes may utilize these molecules as a major reserve of sulfur and also as sources of carbon and energy (Tanabe and Dahl, 2023). Microbially-mediated sulfur cycling can lead to environmental challenges such as the production of toxic and odorous compounds like hydrogen sulfide (H₂S) and several organic sulfur compounds (Wu et al., 2021). Organic sulfur compounds constitute a diverse group of sulfur-containing substances, ranging from small molecules with a C1 carbon skeleton to complex sulfonated lipids (Boden and Hutt, 2018), and those particularly found in fossil fuels contribute significantly to air pollution and environmental contamination. These compounds constitute 4–30 % of the organic aerosol mass in the atmosphere (Li et al., 2023a). Some of the most abundant organic sulfur compounds are dimethyl sulfide (DMS), dimethyl sulfoxide (DMSO), DMSP, sulfoquinovose (SQ), sulfoquinovosyl diacylglycerol (SQDG), 2,3-dihydroxypropane-1-sulfonate (DHPS), thiophene, dibenzothiophene (DBT), taurine, isethionate, cysteine, and methionine (Fig. 1, Table 1).

Due to their natural abundance, microbes frequently encounter and interact with diverse organic sulfur compounds in different ecosystems. The outcome of such interaction is the cornerstone of various environmental, industrial, agricultural, and health-related biotechnological processes ranging from pollution control to green synthesis of specialty chemicals and development of novel probiotics. Microbial biodegradation of organic sulfur compounds is crucial for bioremediation of polluted environments (Wu et al., 2021), plant sulfur supply (Gahan et al., 2022), as well as microbial survival in soil and rhizosphere (Mirleau et al., 2005; Santana et al., 2021). Moreover, utilizing organic sulfur compounds in inexpensive feedstocks, such as petroleum or sulfur-rich waste streams, to produce high-value products remains an economically viable bioprocess (Martínez et al., 2017). Microbial biodesulfurization is a biotechnological approach for eliminating recalcitrant organic sulfur compounds from fossil fuels. Fuel biodesulfurization leverages the exceptional metabolic abilities of certain bacteria that utilize fuel-derived organic sulfur compounds as a sulfur source, thereby lowering the total sulfur content of the bio-treated fuel (Zumsteg et al., 2023).

Generally, the interaction between microorganisms and organic substrates, including organic sulfur compounds, starts with transport into the intracellular milieu. Thus, efficient biocatalysis and biodegradation require the presence of efficient uptake and export systems to ensure optimum concentrations are available to the relevant enzymes and avoid or mitigate toxicity of the substrates and/or products of the biocatalysis. When bacteria grow in the absence of inorganic sulfate, they produce a set of proteins collectively known as the ‘sulfate starvation-induced stimulon’. The synthesis of these proteins is upregulated when sulfate is lacking or during growth with alternative organic sulfur compounds. These proteins mainly include enzymes and transport systems involved in the utilization of organosulfur sources and high-affinity uptake of inorganic sulfate and cysteine (Kertesz, 2001).

The uptake of organic sulfur compounds and the release of their hazardous metabolic intermediates or byproducts are significant impediments to effective biocatalytic transformation processes. Engineering transporters to optimize intracellular sulfur availability may be a viable research avenue to improve the breakdown of organic sulfur compounds and enhance biodesulfurization efficiency (Hou et al., 2023). Hence, better understanding of the uptake mechanisms of organic sulfur compounds is essential for leveraging microbial sulfur metabolism, developing biotechnological applications, and addressing environmental challenges related to sulfur pollution. In this review, we delve into and discuss research on membrane transport systems of organic sulfur compounds, with a focus on structural and functional diversity and implications in diverse fields of biotechnology. Moreover, through gap analysis, we identify and propose key research areas that could advance the field and facilitate the development of more effective biotechnological applications. The discussion is revolving around a group of organic sulfur compounds which we selected based on three primary criteria: (1) industrial significance, exemplified by thiophenes which are common in fossil fuel processing technologies (Awadh et al., 2020; Kilbane II, 2006); (2) environmental prevalence and ecological importance; e.g., DMSP and its derivatives which serve as crucial intermediates in the global sulfur cycle and affect atmospheric processes (Curson et al., 2011; Li et al., 2024); and (3) depth of existing research, where taurine and sulfoacetate are examples of compounds that have well-defined microbial transport and metabolic pathways (Eichhorn et al., 2000).