Research in my laboratory is focused on gaining a better understanding of the structure and function of environmental microbiota in both, terrestrial and aquatic ecosystems. With the development and successful applications of 16S ribosomal gene based molecular techniques, direct correlations between the structure and function of microbial communities can be obtained and utilized to gauge ecosystem health and processes. My laboratory utilizes a polyphasic approach by using traditional culture based tools such as most probable number estimates (MPNs) and community level physiological profiling (CLPP) coupled with molecular tools based on the SSU rDNA analyses such as molecular cloning, restriction fragment length polymorphism (RFLP), and denaturing gradient gel electrophoresis (DGGE). We are also using stable isotope probing (SIP) to link the structure to the function of carbon/nitrogen cycling bacterial guilds in different ecosystems. These approaches have previously provided critical cues on effects of eutrophication on Florida Everglades and Blue Cypress Marsh carbon cycling pathways. We are now using similar approaches to examine perturbations caused to soil productivity in bauxite mined soils in Jamaica and measure the efficacy of restoration activities in a project funded by JAMALCO Inc., a subsidiary of Aluminum Company of America (http://www.alcoa.com/global/en/home.asp). Comparisons obtained between unmined and chronosequentially restored mined sites provide conclusive evidence that mining operations result in severe perturbations to the soils such that impacted soils remain significantly low in productivity most likely due to permanent removal/inhibition of critical soil microbiota such as Proteobacteria, Bacteroidetes group, high G C Gram-positives etc. All these groups are known to rapidly remineralize soil organic matter resulting in increased soil productivity. 

      In the realm of aquatic microbial ecology, we have utilized cutting-edge molecular coupled with traditional methods to identify microbial food web processes and dynamics in Apalachicola Bay, Florida (http://www.famu.edu/index.cfm?a=hbcurise&p=Overview). In estuarine systems, bacterial community succession is a function of top down (grazing, viral lyses) and bottom up (organic and inorganic nutrient supply) factors but little information exists on ‘sideways’ controls, such as bacterial predation by Bdellovibrio-like organisms (BLOs), which likely impact carbon cycling within the microbial loop and eventual export to higher trophic groups. We have extensively studied the sideways impact of bacterial predation in short term events such as tidal cycles. Our results have demonstrated that these factors work in tandem, resulting in bacterial structural and functional successions. An improved understanding of these tightly coupled microbial predator-prey interactions and the effects of DOM supply will lead to a better understanding of carbon cycling processes within the microbial loop in coastal systems. We have also initiated applied research to exploit the predator Bdellovibrio-like organisms (BLOs) as a bio-control agent to effectively control or eliminate contamination by Gram-negative pathogens in food and oyster models. Our prototype is to investigate the combined effects of bacteriophage and BALOs as ‘live antibiotics’ to reduce Vibrio spp., which are often found in high numbers in oysters and other sea foods.

      We are also interested in obtaining a better understanding of the bacterial community structure in surface, bottom waters and oyster microbiome in estuarine systems. Oysters are filter-feeders and accumulate large numbers and diversity of microscopic marine microorganisms in their nutrient-rich mucosa, including pathogens such as Vibrio, Aeromonas, Plesiomonas, Salmonella, Shigella, Escherichia coli O157:H7, and fecal coliforms. Understanding the relationships between aquatic microbial communities and the oyster microbiome, their association with environmental variables, and their variation over spatial and temporal scales will allow development of better indices of oyster health, safety for consumers and mitigation strategies.

      Another recently initiated project aims at characterization of nitrate eutrophication at the watershed scale. The city of Tallahassee, (Florida), recycles municipal wastewater at a water reclamation facility which is then reutilized to grow agricultural crops, watering of golf courses etc. This nutrient rich wastewater, septic tank leachate and runoff from Tallahassee’s downtown and business district watershed has resulted in significant water quality degradation specifically in Wakulla Springs, which is situated downstream to the agricultural spray field watershed and linked through the aquifer system. We are using a multi-pronged approach to remediate the nitrate eutrophication problems in these inter-linked ecosystems through a rigorous and highly integrated research, education, public outreach and extension components.           

A long term research interest also lies in the biodegradation of recalcitrant compounds by soil bacteria to obtain a better understanding of the basis of biodegradation of nitrophenols and naphthalene at the genetic and biochemical level.           


Publications (reprints available upon request)

Chauhan, A., J. Cherrier and H. N Williams. 2009. Impact of Sideways and Bottom up Control Factors on Bacterial Community Succession over a Tidal Cycle. Proc. Natl. Acad. Sci. USA 106(11): 4301-4306.
Chauhan A., G. Fortenberry, D. Lewis and H.N. Williams. 2009. Increased Diversity of Predacious Bdellovibrio- and like Organisms as a Function of Eutrophication in Kumaon Lakes of India. Curr. Microbiol. In Press. DOI 10.1007/s00284-009-9385-z.
Chauhan, A., and H. N Williams. 2008. Biostimulation of Estuarine Microbial Community on Substrate Coated Agar Slides: A Novel Approach to Study the Phylogeny of Bdellovibrio-and Like Organisms. Micro. Ecol. 55: 640-650.
Silvia A. Pineiro, Stine O.C., Chauhan A., Steyert S.R., Smith R., and Williams H.N. 2007. A global survey of diversity among environmental salt water Bacteriovoracaceae. Environ. Microbiol. 9(10): 2441-2450.
Ilker Uz, Chauhan A., and A.V. Ogram. 2007. Cellulolytic, Fermentative, and Methanogenic Potential in Benthic Periphyton Mats from the Florida Everglades. FEMS Microbiology Ecology. 61:337-347.
Chauhan, A. and A.V. Ogram. 2006. Phylogeny of Acetate Utilizing Anaerobic Community along a Nutrient Gradient in the Florida Everglades. Appl. Environ. Microbiol. 72:6837-6840.
Chauhan, A. and H. N Williams. 2006. Response of Bdellovibrio and Like Organisms (BALOs) to the migration of naturally occurring bacteria to chemo attractants. Current Microbiology 53(6): 516-522.
Chauhan A. and A.V. Ogram. 2006. Fatty acid-oxidizing consortia along a nutrient gradient in the Florida Everglades. Appl. Environ. Microbiol. 72:2400-2406.
Chauhan A. A.V. Ogram and K.R. Reddy. 2006. Syntrophic archaeal associations differ with nutrient impact in a freshwater marsh. J. Appl. Microbiol. 100: 73-84.
Chauhan A. and A.V. Ogram. 2005. Evaluation of support matrices for immobilization of anaerobic consortia for efficient carbon cycling in waste regeneration. Biochem. Biophys. Res. Commun. 327:884-893.
Chauhan A., A.V. Ogram, and K.R. Reddy. 2004. Novel syntrophic-methanogenic associations along a nutrient gradient in the Florida Everglades. Appl. Environ. Microbiol. 70:3475-3484.
Debarati Paul, A. Chauhan, Gunjan Pandey and Rakesh K. Jain. 2004.  Degradation of p-hydroxybenzoate via protocatechuate in Arthrobacter protophormiae RKJ100 and Burkholderia cepacia RKJ200. Current Science 87(9): 1263-1268.
Chauhan A. and A.V. Ogram. 2003. Immobilization of anaerobic bacterial consortia for efficient carbon cycling in a proposed novel closed ecological life support system (CELSS) coupling rice rhizosphere to waste regeneration Habitation (Elmsford). 9(3-4):89-218.
Pandey G, A. Chauhan, SK, Samanta and R.K. Jain. 2002. Chemotaxis of a Ralstonia sp. SJ98 toward co-metabolizable nitroaromatic compounds. Biochem. Biophys. Res. Commun. 299:404-409.
Chauhan, A., A.K., Chakraborti, and R.K. Jain. 2000. Plasmid-encoded degradation of p-nitrophenol and 4-nitrocatechol by Arthrobacter protophormiae. Biochem. Biophys. Res. Commun. 270:733-40.
Chauhan, A., S.K., Samanta, and R.K. Jain. 2000. Degradation of 4-nitrocatechol by Burkholderia cepacia: a plasmid-encoded novel pathway. J. Appl. Microbiol. 88:764-72.
Chauhan, A., and R.K. Jain. 2000. Degradation of o-nitrobenzoate via anthranilic acid (o-aminobenzoate) by Arthrobacter protophormiae: a plasmid-encoded new pathway. Biochem. Biophys. Res. Commun. 267:236-44.
Bhushan, B., A. Chauhan, S.K., Samanta, and R.K. Jain. 2000. Kinetics of biodegradation of p-nitrophenol by different bacteria. Biochem. Biophys. Res. Commun. 274:626-630.
Bhushan, B., S.K., Samanta, A. Chauhan, A.K., Chakraborti, and R.K. Jain. 2000. Chemotaxis and biodegradation of 3-methyl- 4-nitrophenol by Ralstonia sp. SJ98. Biochem. Biophys. Res. Commun. 275:129-33.
Samanta, S.K., B. Bhushan, A. Chauhan, and R.K. Jain. 2000. Chemotaxis of a Ralstonia sp. SJ98 toward different nitroaromatic compounds and their degradation. Biochem. Biophys. Res. Commun. 269:117-23.
Prakash, D., A. Chauhan, and R.K. Jain. 1996. Plasmid-encoded degradation of p-nitrophenol by Pseudomonas cepacia. Biochem. Biophys. Res. Commun. 224:375-81.
Book Chapter (by invitation only):

Andrew Ogram, Hector Castro, and Ashvini Chauhan. 2007. Methods of Soil Microbial Community Analysis. in C. J. Hurst, R. L. Crawford, J. L. Garland, D. A. Lipson, A. L. Mills, and L. D. Stetzenbach, editors. Manual of Environmental Microbiology, 3rd edition. ASM Press, Washington, D.C., Pages 652-662.
Manuscripts under review (preprints available upon request)

Ogram, A., Chauhan, A., Inglett, K., Jayachandran, K., and S. Newman. 2009. Linking Nutrient Impacts on Microbial Community Structure and Function with Biogeochemistry in the Everglades.
Manuscripts under preparation (preprints available upon request)

Chauhan A. and A.V. Ogram. 2009. Evidence that salicylate is not involved in the metabolic pathway for naphthalene degradation in Rhodococcus opacus strain M213: a new pathway operative via o-phthalate. Planned submission in Applied and Environmental Microbiology.
Chauhan A., H.F. Castro, K.R. Park, K.R. Reddy and A.V. Ogram. 2009. Vertical distribution of methanogenic archaea within a nutrient gradient in the Florida Everglades. Planned submission in Applied and Environmental Microbiology.
Chauhan A., A.V. Ogram, and K.R. Reddy. 2009. Stable isotope probing of the methanotrophic community along a nutrient gradient in the Florida Everglades. Planned submission in Applied and Environmental Microbiology.