Research Interests

Prokaryotic sulfur oxidation and origin of Life on Earth

The deepest-rooted branches of Bacteria and Archaea encompass chemolithotrophic thermophiles having bioenergetics based on redox transformations of inorganic substrates like sulfur and its compounds. As such, lithotrophic sulfur oxidation, encountered in almost all the major prokaryotic groups, is thought to be an ancient metabolic process. The fact that the extreme environmental conditions (like abundance of reducing gases like H₂S, CO₂ and H₂) of the early Earth resembled those prevailing in today’s geothermal ecosystems also lend credence to the notion that early life forms were similar to the extant hyperthermophilic chemolithotrophs that inhabit terrestrial or deep-sea hydrothermal systems where oxidation of reduced sulfur species (and also CH₄ and H₂) is the primary source of energy.

Elucidation of the origin and evolution of sulfur-lithotrophy is thus central to the understanding of the metabolic strategies of early Life. The eventual goal is to identify the molecular strategies that the early lithotrophs used to (a) establish oxidative metabolism in overwhelmingly reduced environments and (b) then transform them to suit increasingly-oxidative regimes. Towards this end we study the origins (paleo- and geobiology), evolution (phylogeny) and interactions of the different molecular systems governing sulfur oxidation in ecologically and taxonomically diverse photo- or chemolithotrophs.

Paleobiology and Geobiology of ancient ecosystems vis-à-vis Astrobiology

Geothermal environments, besides being home to diverse ancient prokaryotic groups, are best suited for microbial fossil preservation by virtue of their versatile and vigorous mineralization processes. So, at the same time as modern hot springs serve as analogs (models for paleontological interpretation) of the putatively ancestral niches of Life, ancient hydrothermal deposits hold valuable information on our early biospheres embedded within. Notably, missions to Mars in search of evidence of Life, past or present, also target areas bearing marks of extinct or active geothermal activity. Siliceous and carbonatic sinters are, so far, the most prominent and well-studied markers (surface manifestations) in the interpretation of past or present geothermal activity in and outside the Earth. Again, efficiency of such accumulates in fossilizing terrestrial extremophilic communities has made them prospective astrobiological targets. However, high temperature biomineralization-fossilization processes, as a whole, are poorly understood. So, these phenomena are of particular concern in my comprehensive paleontological and biogeochemical investigation of geothermal habitats.

Though elucidation of the bioenergetic abilities of thermophilic prokaryotes is regarded as central to the understanding of early metabolism, existing information is largely based on laboratory growth experiments (which too is inadequate as laboratory culture of extremophiles is impossible in a majority of cases) while data on their actual nutritional attributes and preferences in natural habitats is very scarce owing to taxing field logistics and experimental problems. Again, paleontological and biogeochemical research in high temperature geothermal environments all the more difficult. Quantitative data obtained from pure culture experiments are, at best, partially applicable to natural systems and can give little idea of the metabolic processes happening in nature. This is because community interactions, physico-chemical conditions, substrate-transport phenomena, etc., are considerably distinct in nature from the controlled laboratory conditions. Our overall goal is to generate models of present as well as past biogeochemical processes in critical high temperature ecosystems by integrating microbiological, ecological and geological data. As such, we are exploring the actual metabolic and phylogenetic diversity of the microbes inhabiting diverse geothermal niches, their abundance, community metabolic functions and sustainability over geological time periods.

Collaborators

Dr. Aninda Mazumdar
Gas Hydrate Research Group, Geological Oceanography, NIO, DonaPaula, Goa - 403004 

Professor Sujoy Kumar Das Gupta
Department of Microbiology, Bose Institute, Kolkata – 700054

 Dr. Somnath Mallick
Department of Chemistry, Saldiha College, Saldiha, Bankura, West Bengal 

Dr. Bhaskar Bhadra
Industrial Biotech (BCS & E), DuPont Knowledge Centre, Hyderabad - 500078

Publications

1.     Masrure Alam, Chayan Roy, Prosenjit Pyne, Atima Agarwal, Ashish George and Wriddhiman Ghosh (2012) Whole-Genome Shotgun Sequencing of the Sulfur Oxidizing Chemoautotroph Pseudaminobacter salicylatoxidans KCT001. Journal of Bacteriology 194, 4743-4744. 

2.      Wriddhiman Ghosh, Somnath Mallick, Prabir Kumar Haldar, Baishali Pal, Subhas Chandra Maikap and Sujoy Kumar Das Gupta (2012) Molecular and cellular fossils of a mat-like microbial community in geothermal boratic sinters. Geomicrobiology Journal 29, 879 – 885. 

3.     Wriddhiman Ghosh, Ashish George, Atima Agarwal, Praveen Raj, Masrure Alam, Prosenjit Pyne and Sujoy Kumar Das Gupta (2011) Whole-Genome Shotgun Sequencing of the Sulfur-Oxidizing Chemoautotroph Tetrathiobacter kashmirensis. Journal of Bacteriology 193, 5553 – 5554.

4.      Wriddhiman Ghoshand Bomba Dam (2009) Biochemistry and molecular sulfur-oxidation by taxonomically and ecologically diverse bacteria and archaea. FEMS Microbiology Reviews 33, 999 – 1043

5.      Wriddhiman Ghosh, Somnath Mallick and Sujoy Kumar Das Gupta (2009) multienzyme complex system in ancient thermophilic bacteria and coevolution of its constituent proteins. Research in Microbiology 160: 409 – 420. 

6.       Bomba Dam, Wriddhiman Ghosh and Sujoy Kumar Das Gupta (2009) Conjugative Type 4 Secretion System of a Novel Large Plasmid from the Chemoautotroph Tetrathiobacter kashmirensis and Construction of Shuttle Vectors for Alcaligenaceae. Applied and Environmental Microbiology 75, 4362–4373. 

7.       Wriddhiman Ghosh and Pradosh Roy (2007) Chemolithoautotrophic oxidation of thiosulfate, tetrathionate and thiocyanate by a novel rhizobacterium belonging to the genus Paracoccus. FEMS Microbiology Letters 270, 124-131

8.       Bomba Dam, Sukhendu Mandal, Wriddhiman Ghosh, Sujoy Kumar Das Gupta and Pradosh Roy (2007) The S4-intermediate pathway for the oxidation of thiosulfate by the chemolithoautotroph Tetrathiobacter kashmirensis and inhibition of tetrathionate oxidation by sulfite. Research in Microbiology 158, 330-338. 

9.       Wriddhiman Ghosh and Pradosh Roy (2007) Chemolithoautotrophic oxidation of thiosulfate and tetrathionate by novel strains of Azospirillum and Pseudoxanthomonas isolated from the rhizosphere of an Indian tropical leguminous plant. Current Science 93, 1613-1615. 

10.       Wriddhiman Ghosh and Pradosh Roy (2006) Mesorhizobium thiogangeticum sp. nov., a novel sulfur-oxidizing chemolithoautotroph from rhizosphere soil of an Indian tropical leguminous plant. International Journal of Systematic and Evolutionary Microbiology 56, 91-97

11.      Chandrajit Lahiri, Sukhendu Mandal, Wriddhiman Ghosh, Bomba Dam and Pradosh Roy (2006) A novel gene cluster soxSRT is essential for the chemolithotrophic oxidation of thiosulfate and tetrathionate by Pseudaminobacter salicylatoxidans KCT001. Current Microbiology 52, 267-273. 

12.      Wriddhiman Ghosh, Sukhendu Mandal and Pradosh Roy (2006) Paracoccus bengalensis sp. nov., a novel sulfur-oxidizing chemolithoautotroph from the rhizospheric soil of an Indian tropical leguminous plant. Systematic and Applied Microbiology 29, 396-403. 

13.      Wriddhiman Ghosh and Pradosh Roy (2006) Ubiquitous presence and activity of sulfur-oxidizing lithoautotrophic microorganisms in the rhizospheres of tropical plants. Current Science 91, 159-161. 

14.       Wriddhiman Ghosh, Angshuman Bagchi, Sukhendu Mandal, Bomba Dam and Pradosh Roy  (2005) Tetrathiobacter kashmirensis gen. nov., sp. nov., a novel mesophilic, neutrophilic, tetrathionate-oxidizing, facultatively chemolithotrophic betaproteobacterium isolated from soil from a temperate orchard in Jammu and Kashmir, India. International Journal of Systematic and Evolutionary Microbiology 55, 1779-1787. 

15.       Prodosh Roy, Anjan Sengupta, Ranadhir Chakraborty, Chandrajit Lahiri and Wriddhiman Ghosh. (2002) Chemotaxis of Acidithiobacillus ferrooxidans vis-à-vis mineral-microbe interaction. In Mineral Biotechnology, pp. 43-57. Edited by L. B. Sukla and V. N. Misra. New Delhi: Allied Publishers.