The widespread use of azo dyes in the textile, food, and leather industries results in the production of large volumes of wastewater, which is considered a major threat to ecosystems and human health. These dyes inhibit photosynthesis in water and may release carcinogenic aromatic amines. Traditional physicochemical methods are usually expensive and energy intensive and produce secondary xenobiotics; therefore, greener methods are needed. Bioremediation with the help of bacteria has become a potential, environmentally friendly, and yet economically viable tool for addressing azo dye pollution. In particular, this review examines the effectiveness of Bacillus spp. in the degradation and detoxification of different azo dyes in textile effluent. It describes the enzymatic processes, especially the involvement of azoreductases and other oxidoreductive enzymes, by which such bacteria break recalcitrant azo bonds under both aerobic and anaerobic conditions. New technological progress in maximizing these microbial processes, such as the effects of key physicochemical variables and the evolution of sophisticated bioreactor technologies to increase degradation and scalability, is discussed. Nevertheless, the buy-down process in the lab in the field is not without challenges, including the complexity of dye structures, the stability of the dye in mixed waste streams, and optimization of the process. These hurdles, which are discussed critically in this review, and future directions, such as genetic engineering of strong bacterial strains and complementing biological approaches with other technologies, are the way forward in ensuring the sustainable treatment of industrial wastewater.
1,2-Dichloropropane (1,2-DCP) is a highly toxic chlorinated aliphatic hydrocarbon, and in situ bioremediation represents a primary strategy for mitigating its environmental risk. However, how nutrient availability drives the structural succession and functional reorganization of 1,2-DCP-degrading communities remain unclear. Using contaminated soils as the inoculum, parallel enrichment systems were constructed, comprising an oligotrophic system utilizing 1,2-DCP as the sole carbon source, and a copiotrophic cometabolic system supplemented with complex carbon sources. Sequencing analyses indicated that oligotrophic conditions drove community succession toward a highly diverse state dominated by Proteobacteria via substrate limitation. Conversely, the copiotrophic cometabolic regime shaped a heterotrophic structure dominated by Firmicutes through competitive exclusion. Guided by these succession patterns, the isolation process yielded four degrading strains that were identified as Microbacterium proteolyticum, Stutzerimonas stutzeri, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Genomic annotations revealed a potential aerobic degradation network integrating monooxygenase catalysis, oxidoreductase-mediated electron transfer, and glutathione-dependent cellular defense mechanisms. These findings confirm that nutrient input regimes are the core drivers of microbial community succession trajectories, providing a theoretical basis and biological resources for the targeted bioremediation of recalcitrant halogenated organics.
This study explored the identification of thermophilic biosurfactants producing bacteria and their potential for heavy used engine oil (HUEO) degradation with and without supplementation of exogenous surfactant. Among the various isolated bacteria Bacillus stercoris S1M and Brevibacillus agri ST2 were selected as potent biosurfactants producing and hydrocarbon (i.e., HUEO) degrading bacteria under thermophilic (50 degrees C) condition. Both strains viz. S1M and ST2 were found to be efficient biosurfactants producers with significant oil displacement activity (ODA) and emulsification indices (EI24%), with 29.5 +/- 2.12 to 18.5 +/- 4.94 mm ODA, and 65.25 +/- 8.72 to 33.33 +/- 9.42% EI to Kerosene oil, respectively). HUEO degradation under thermophilic conditions was evaluated for both strains and defined co-culture. The addition of exogenous surfactant further enhanced biodegradation efficiency for Bacillus stercoris S1M (increased from 46.40 +/- 7.8 to 64.87 +/- 14.00%), confirming their role in improving hydrocarbon bioavailability. Brevibacillus agri ST2 degradation increased modestly (70.77 +/- 13.13 to 74.77 +/- 1.46%) and its co-culture (66.39 +/- 10.51 to 76.36 +/- 7.22%). However, exogenous surfactant exerted an inhibitory effect on the growth of Brevibacillus agri ST2, and in the co-culture. This study demonstrates a novel dual role of surfactant in thermophilic hydrocarbon degradation. It acts not only as a bioavailability enhancer which significantly enhanced HUEO degradation by S1M and its co-culture, but also a potent disruptor of microbial synergy, possessing a growth-inhibitory effect on a key degrading partner i.e., ST2 strain. This reveals a critical strain-specific tradeoff between the metabolic enhancement and ecological interactions in designed bioremediation consortia.
