5:15 PM - 6:45 PM
[BPT02-P01] The Role of Halophilic Bacteria in Dolomite Precipitation: Investigating the Influence of Bacterial Activity and Extracellular Polymeric Substances
Keywords:dolomite, halophilic bacterium, extracellular polymeric substances, EPS, polysaccharide
Dolomite [CaMg(CO3)2] is a carbonate mineral commonly found in ancient rocks, particularly during the Cretaceous, Triassic, and Precambrian eras, where it is abundant. However, dolomite occurrence is limited in modern environments, mainly appearing in small quantities in hypersaline lakes and methane cold seeps during the Holocene era. The synthesis of dolomite under normal temperatures and pressures poses challenges. Dolomite formed at room temperature lacks cation ordering, meaning that the arrangement of calcium and magnesium ions is not in alternating layers. Additionally, dolomite precipitation does not occur in seawater, despite modern seawater being supersaturated with respect to dolomite. These long-standing challenges in dolomite research, referred to as the "dolomite problems," have puzzled scientists for about a century.
It is believed that the difficulty in dolomite precipitation at normal temperature and pressure is attributed to the strong hydration shell formed by magnesium, which inhibits CO3 binding (Warren 2000). However, the presence of polysaccharides leads to the carboxyl groups attempting to bind with water. This competition weakens the binding strength of the hydration shell, enabling the formation of disordered dolomite with a random arrangement of calcium and magnesium (Zhang et al., 2020). Certain bacteria, such as sulfate-reducing bacteria, are known to promote the formation of disordered dolomite. However, it remains unclear whether this effect is due to the bacteria producing extracellular polymeric substances (EPS), primarily composed of polysaccharides, or if it is the bacterial activity itself that induces dolomite precipitation. One proposed idea suggests that EPS strongly influence precipitation, rendering microbial life activities unnecessary (Bontognali et al., 2013). Conversely, other study has concluded that microbial life activities are vital for Magnesian calcite precipitation (Rivadeneyra et al., 2004).
In this study, we investigate whether sterilized biofilm produced by the dolomite-precipitating aerobic halophilic bacterium Halomonas meridiana can facilitate dolomite precipitation. A unique aspect of our research is the termination of bacterial life activities at a relatively low temperature of 50 degrees Celsius, without utilizing an autoclave. Autoclaves, commonly employed for sterilization, can potentially compromise the composition of EPS due to high temperatures. By avoiding excessive thermal alteration of EPS, we mitigated potential negative impacts on our experimental results. Additionally, we employed solid cultures to replicate a biofilm found in hypersaline lakes.
Our experiments revealed that when the dolomite-precipitating aerobic halophilic bacterium Halomonas meridiana was inoculated into a solid medium resembling seawater, disordered dolomite was formed. However, when sterilized biofilm at 50 degrees Celsius, comprised of dead bacteria and EPS, was inoculated, no dolomite was generated. These results provide evidence that the activity of the bacteria itself has the ability to induce dolomite precipitation.
It is believed that the difficulty in dolomite precipitation at normal temperature and pressure is attributed to the strong hydration shell formed by magnesium, which inhibits CO3 binding (Warren 2000). However, the presence of polysaccharides leads to the carboxyl groups attempting to bind with water. This competition weakens the binding strength of the hydration shell, enabling the formation of disordered dolomite with a random arrangement of calcium and magnesium (Zhang et al., 2020). Certain bacteria, such as sulfate-reducing bacteria, are known to promote the formation of disordered dolomite. However, it remains unclear whether this effect is due to the bacteria producing extracellular polymeric substances (EPS), primarily composed of polysaccharides, or if it is the bacterial activity itself that induces dolomite precipitation. One proposed idea suggests that EPS strongly influence precipitation, rendering microbial life activities unnecessary (Bontognali et al., 2013). Conversely, other study has concluded that microbial life activities are vital for Magnesian calcite precipitation (Rivadeneyra et al., 2004).
In this study, we investigate whether sterilized biofilm produced by the dolomite-precipitating aerobic halophilic bacterium Halomonas meridiana can facilitate dolomite precipitation. A unique aspect of our research is the termination of bacterial life activities at a relatively low temperature of 50 degrees Celsius, without utilizing an autoclave. Autoclaves, commonly employed for sterilization, can potentially compromise the composition of EPS due to high temperatures. By avoiding excessive thermal alteration of EPS, we mitigated potential negative impacts on our experimental results. Additionally, we employed solid cultures to replicate a biofilm found in hypersaline lakes.
Our experiments revealed that when the dolomite-precipitating aerobic halophilic bacterium Halomonas meridiana was inoculated into a solid medium resembling seawater, disordered dolomite was formed. However, when sterilized biofilm at 50 degrees Celsius, comprised of dead bacteria and EPS, was inoculated, no dolomite was generated. These results provide evidence that the activity of the bacteria itself has the ability to induce dolomite precipitation.