Evidence of a Role for Aerobic Bacteria in High Magnesium Carbonate Formation in the Evaporitic Environment of Dohat Faishakh Sabkha in Qatar

Abstract

Dolomite (MgCa(CO 3 ) 2 ) is an important petroleum reservoir rock mineral common in ancient sedimentary rocks which is infrequently found in modern environments. The mechanism of dolomite formation remains poorly understood, although recent research has focused on the contribution of microbial processes. Sabkha is the Arabic term for saline mudflats occurring in regions characterized by extreme environmental conditions (high temperature, salinity, light intensity, and aridity), where diverse halophilic and extremophilic microorganisms are found. The dynamic evaporitic systems characteristic of sabkhas are crucial for the precipitation of minerals and a role for microorganisms in sabkhas in the process of mineralization has been proposed. In this study the Dohat Faishakh Sabkha in Qatar was investigated for evidence of the role for aerobic bacteria in mediating the formation of high magnesium carbonates and dolomite, two minerals that commonly occur in the sabkha sediments. Twenty-nine strains of aerobic microbes were obtained through inoculation on agar plates from two different cores sampled from the sabkha and identified by 16S rRNA gene sequencing as belonging to the genera Bacillus, Salinivibrio, Staphylococcus and, primarily, Virgibacillus. All strains examined caused the pH of an artificial growth medium to increase from 7 to 8.5; however, not all were capable of mediating mineral formation. Only Salinivibrio and Virgibacillus spp. isolates mediated the formation of detectable solid phases within the agar plates. Light microscopy, scanning electron microscopy energy dispersive X-ray (SEM/EDX), and X-ray diffraction (XRD) analyses indicate that the solid phase produced in the presence of these bacterial strains is MgCa(CO 3 ) 2 with a MgCO 3 mol% varying from 0 to 40%. The results of these laboratory experiments suggested that, in the Dohat Faishakh Sabkha, aerobic bacteria may contribute in the formation of very high Mg calcite, a mineral that is considered the precursor of ordered dolomite.

Microbe‐Mediated Extracellular and Intracellular Mineralization: Environmental, Industrial, and Biotechnological Applications

“…contribute to the formation of MgCa(CO 3 ) 2 , which is considered the precursor of ordered dolomite. [ 7 ] Biotic precipitation of CaCO 3 accounts for nearly 80% of the total carbon removal from the earth's surface. [ 8 ] Calcifying bacteria such as Bacillus sphaericus have been used for biodeposition of CaCO 3 crystals on the surface of limestone for conservation purposes.…”

Alginate‐Encapsulated Bacteria for the Treatment of Hypersaline Solutions in Microbial Fuel Cells

“…The characteristics of colonies and cells were similar to those bacteria described in previous studies regarding the isolation of other Salinivibrio sp. strains . Thus, molecular identification of isolate EAGSL was carried out, and the resulting sequence was analyzed by using the DNA BLAST database to find the most similar strains.…”

“…Molecular identification of EAGSL isolate : One of the isolated colonies, named EAGSL (Electro‐Active Great Salt Lake), was grown on fresh SRB medium for 48 h. The cells were harvested, and the 16S rRNA gene was amplified by PCR as described previously by using forward primer RibS73sp AGAGT TTGAT CCTGG CTCA and reverse primer RibS74sp AAGGA GGTGA TCCAG CCGCA . The PCR product was purified by using a PCR purification kit (Qiagen) prior to DNA sequencing.…”

Carbonate and silicate biomineralization in a hypersaline microbial mat (Mesaieed sabkha, Qatar): Roles of bacteria, extracellular polymeric substances and viruses

“…3B). Dolomite has recently been recorded in microbial mats on the west side of Qatar at Dohat Faishakh (Brauchli et al, 2016;Al Disi et al, 2017), although this area was one of those sites in the Arabian Gulf from which dolomite was described back in the 1960s (Illing et al, 1965).…”