Biogenic Evidences of Moonmilk Deposition in the Mawmluh Cave, Meghalaya, India

Abstract

Moonmilk, a microcrystalline secondary cave deposit, actively forms on the floor of Krem Mawmluh – a limestone cave in Meghalaya, Northeastern India. Due to the abundance of micrite and calcified microbial filaments, we hypothesize that these deposits form as a result of ongoing microbial interactions. Consistent with this idea, we report electron microscopic and microbiological evidences for the biological origin of moonmilk in Krem Mawmluh. Scanning electron microscopy indicated abundant calcified microbial filaments, needle calcite, fibre calcites (micro-fibre and nano-fibre calcite crystals), biofilm and microbial filaments in the moonmilk. The total viable culturable microbes showed high population densities for microbes in the moonmilk and moonmilk pool waters. In vitro culture experiments, confirmed the capability of many of the isolated strains to precipitate calcite and some of the identified isolates belonged to the Bacillus sp. and Actinomycetes. These results clearly support the biogenic nature of the deposits.

Keywords:

• Geomicrobiology
• Caves
• Moonmilk
• Bacteria
• Calcite precipitation

Acknowledgments

The Director, Wadia Institute of Himalayan Geology, Dehradun is thanked for the SEM, thin section petrography and ICP-MS data. Marianne Ahlbom, Anna Neubeck and Paula Lindgren at Stockholm University are thanked for helping with the ESEM-EDAX analysis. Dr. R. Heuchel, at Karolinska Institute helped with optical microscopy. Institute for Microbial Technology, Chandigarh (IMTECH) is acknowledged for identification of cultures. P.K. Theophilus assisted with sample collection and fieldwork. Constructive and helpful suggestions from Diana E. Northup and an anonymous reviewer greatly improved the manuscript. SB thanks the Swedish Institute for a postdoctoral fellowship. RB thanks UGC, New Delhi for financial assistance. The study was funded by SASNET and SIDA.