Research Projects

The magnetotactic bacteria (MTB) are a morphologically, phylogenetically, and physiologically diverse group of bacteria and make a distinctive constituent of the aquatic microbiome due to their unique magneto-responsive capability which allows them to navigate to their favored microenvironments efficiently. Apart from iron biomineralization (producing magnetic nano-particles such as magnetite and greigite), MTB can fix nitrogen, oxidize/reduce sulfur, and sequester carbon and phosphorus from the environment and therefore plays an important role in the biogeochemical cycle of the elements. Recent discoveries of several new phyla of MTB highlight our limited knowledge of their ecology and diversity and their contribution to the biogeochemical cycles of elements. Only a few studies on MTB from the Indian lakes have been carried out and therefore, their ecology and diversity in the Indian context is largely missing. After death, MTB is converted to fossil magnetosome (magnetite and greigite) that efficiently record the geomagnetic field strength and thus hold clues for the paleomagnetism and paleoclimate. The proposal's objectives are: 1. To identify the MTBs and magnetofossils in the Indian lake sediments, 2. Assessing geological, climatological, and biogeochemical limiting factors on MTB abundance in the lakes. 3. To understand the microenvironments of the MTB and magnetofossils in the lakes. 4. To establish magnetofossils as a novel proxy for paleoclimatic changes during the Holocene. To achieve the proposed objectives, we will employ multi-disciplinary (environmental magnetism, total organic carbon (TOC), major and trace element geochemistry, geochronology) methods on two natural lakes from the Himalayas and Peninsular India having different climatological, topographic, and fresh/saline water characteristics. Surface water-sediment samples will be collected from the shallow water lake shore regions as well as the center of the lake. Four short sediment cores (1 m) will be raised from each lake. The magnetofossils from these cores will be separated using the magnetic particle extraction method and will be studied for morphology using electron microscopy. Advanced rock magnetic methods such First Order Reversal curve (FORC) diagrams and magnetic coercivity unmixing using Isothermal remanent magnetization (IRM) will be used for the magnetofossils identification in sediments. TOC and major and trace elements will be analyzed for the nutrient supply and their role as limiting factors for MTB growth. The long sediment cores/trench (2 m) will be raised for paleoclimatic studies. The cores will be dated using AMS14C chronology, and detailed rock magnetic and geochemistry along with organic carbon isotope will be studied. The magnetofossils abundance will be then evaluated with respect to these paleoclimatic proxies for their suitability as a novel proxy for the paleoclimate.