Microbial diversity of drilling fluids from 3000 m deep Koyna pilot borehole provides insights into the deep biosphere of continental earth crust

Abstract

Abstract. Scientific deep drilling of the Koyna pilot borehole into the continental crust up to a depth of 3000 m below the surface at the Deccan Traps, India, provided a unique opportunity to explore microbial life within the deep granitic bedrock of the Archaean Eon. Microbial communities of the returned drilling fluid (fluid returned to the mud tank from the underground during the drilling operation; designated here as DF) sampled during the drilling operation of the Koyna pilot borehole at a depth range of 1681–2908 metres below the surface (m b.s.) were explored to gain a glimpse of the deep biosphere underneath the continental crust. Change of pH to alkalinity, reduced abundance of Si and Al, but enrichment of Fe, Ca and SO42- in the samples from deeper horizons suggested a gradual infusion of elements or ions from the crystalline bedrock, leading to an observed geochemical shift in the DF. Microbial communities of the DFs from deeper horizons showed progressively increased abundance of Firmicutes, Gammaproteobacteria and Actinobacteria as bacterial taxa and members of Euryarchaeota as the major archaeal taxa. Microbial families, well known to strive in strictly anaerobic and extremophilic environments, (e.g. Thermoanaerobacteraceae, Clostridiaceae, Bacillaceae, Carnobacteriaceae, Ruminococcaceae), increased in the samples obtained at a depth range of 2000 to 2908 m b.s. Phylogenetic analysis of common and unique operational taxonomic units (OTUs) of DF samples indicated signatures of extremophilic and deep subsurface relevant bacterial genera (Mongoliitalea, Hydrogenophaga, Marinilactibacillus, Anoxybacillus, Symbiobacterium, Geosporobacter, Thermoanaerobacter). Thermophilic, obligatory anaerobic sulfate-reducing bacterial taxa known to inhabit the deep subsurface were enriched from DF samples using sulfate as a terminal electron acceptor. This report on the geomicrobiology of the DF obtained during drilling of the deep subsurface of the Deccan Traps showed new opportunities to investigate deep life from terrestrial, granite-rock-hosted habitats.

Biodegradation of Unpretreated Low-Density Polyethylene (LDPE) by Stenotrophomonas sp. and Achromobacter sp., Isolated From Waste Dumpsite and Drilling Fluid

“…Kowalczyk et al, 2016;Muhonja et al, 2018;Park and Kim, 2019). Regarding the microorganisms of drilling fluids used in deep subsurface drilling operations, various studies have reported their taxonomic versatility and biodegradation potential (Alekhina et al, 2007;Bilkay, 2017, 2018;Bose et al, 2020). Plastic metabolizing ability of such bacteria, however, has not been explored in detail.…”

“…Waste plastic samples were collected from the local landfill site (designated as P) inside the IIT Kharagpur campus (22 • 18' 45.3" N 87 • 19' 28.1" E). The drilling fluid (designated as DF2, DF4, DF7) samples were collected during a 3 km deep pilot borehole (KFD-1) drilling in the Koyna region (17 • 24' 6" N 73 • 45'8" E) of the Deccan Traps, Maharashtra under the pilot phase of the Koyna scientific drilling project (Bose et al, 2020;Roy and Bansal, 2020). The various depths were as follows: DF2: 1901.255 mbs; DF4:2335.62 mbs; DF7: 2908.52 mbs (mbs: meters below surface).…”

Coupled C, H, N, S and Fe biogeochemical cycles operating in the continental deep subsurface of the Iberian Pyrite Belt

“…Members of the Cyanobacteria class and the Acidithiobacillus , Acidovorax , Desulfosporosinus , Pseudomonas , Sulfobacillus and Tessaracoccus genera were detected in 13 out of 19 analysed intervals, using at least three independent methodologies. As mentioned, Cyanobacteria had been previously reported in several drilling operations (Bose et al, 2020 ; Dutta et al, 2018 ; Gihring et al, 2006 ; Momper, Reese, et al, 2017 ) and in samples from borehole BH10 (Puente‐Sánchez et al, 2018 ), indicating the existence of non‐photosynthetic alternative metabolisms, such as the use of H 2 , in this important group of microorganisms. Moreover, we have previously isolated and characterized an endogenous IPB subsurface nitrate‐reducing bacterium from the same drilling, Tessaracoccus lapidicaptus (Puente‐Sánchez, Sánchez‐Román, et al, 2014 ).…”

High Abundance of Thaumarchaeota Found in Deep Metamorphic Subsurface in Eastern China

“…These aerobic members included Thaumarchaeota (proved to be AOA in the following phylogenetic analysis, about 12.8% in relative abundance in the biofilm sample) [ 41 , 42 ], Gaiella (6.6%) [ 43 ], Methylobacterium (6%) [ 44 ], and Solirubrobacter (1.7%) [ 45 ]. The high abundance of aerobes distinguish the microbial community in the CCSD biofilm sample from most anaerobe-dominated microbial communities of the continental subsurface [ 46 , 47 , 48 ].…”