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Chemolithotrophy is oxidations of inorganic substances fulfill the nutritional requirements of the organisms. Genomic studies revealed soxSRT and soxVWXYZABCD which governs chemolithotrophy. Four proteins, SoxXA, SoxYZ, SoxB and SoxCD, forms multienzyme complex system (TOMES) to carry out oxidation of thiosulfate. Sequence analysis of sox operon showed various promoters and regulatory genes soxSRT, codes for thioredoxin, transcriptional regulator and a transporter protein. Little was known about the regulational control of the sox gene expression that motivated to investigate the gene regulation. The soxR- mutants exhibited constitutive gene expression. The SoxR binds to two promoter-operator within the sox cluster, one (wx) located between soxW and soxX controls the expression of soxX to soxD, while the other, a bi-directional element (sv), located between soxS and soxV, controls the expression of soxVW and regulatory cluster soxSRT. The molecular mechanism behind this important mode of bacterial nutrition could be generalized as a model gene regulational system and could widely be useful for researcher as well as general UG and PG students of basic and applied microbiology.

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Sukhendu Mandal studied M. Sc. at Visva-Bharati University and doctoral research at Bose Institute, India on molecular microbiology. Worked at Waksman Institute, USA with Prof. Richard Ebright on RNA polymerase. Now Assistant Professor of Microbiology at University of Calcutta. Working on bacterial transcriptions. Teaches basic microbiology.

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