Abstract
Bacterial weathering plays a significant role in rock weathering, yet only a limited number of studies were conducted on this topic. The recent rapid developments in geomicrobiology are expected to increase the pace of research in this area. The extent and duration of the biological weathering processes on mineral and rock samples and minerals preferred by bacteria are still not fully understood due to the wide variety of both bacterial species and rock types. Biological weathering of rock types found in Turkey has also not been studied before. Here, we investigated the effects of two species of bacteria actively contributing to rock weathering on three rock types commonly used as building stone materials in Turkey. Granite, andesite, and limestone samples could interact with Bacillus species (B. subtilis and B. pumilus) in closed system reactors. Samples obtained from these reactors were analysed via scanning electron microscopy (SEM) monitoring to identify morphological features and chemical composition changes. Chemical elements consumed most by bacteria were identified. Changes in the colour index were determined via RGB measurements. The effects of experimental conditions on bacterial growth were monitored via daily optical density measurements. The effects of bacteria on the physical properties of rock samples were also evaluated. B. subtilis and B. pumilus were found to be more aggressive on limestone/andesite and granite, respectively.
Highlights
Rock decay is described as the adaptation of rocks to varying physicochemical conditions on the ground surface (Ehrlich 2002)
Apparent porosity and void ratio changes of rock samples contacting B. subtilis and B. pumilus were higher with the NB- condition (Fig. 14–15)
The decrease in the apparent porosity was observed to occur as a result of the placement of the nutrients within the pores and biofilm formation
Summary
Rock decay is described as the adaptation of rocks to varying physicochemical conditions on the ground surface (Ehrlich 2002). Mineralogical components of rocks are altered and modified upon exposure to earth surface conditions in response to different atmospheric agents and insolation that may result in disaggregation (physical weathering) or decomposition (chemical weathering) of the rock. Biological impact, especially that of microorganisms, is the most critical factor controlling the amount and speed of rock decay (Gorbushina and Krumbein 2005). The primary effect of microorganisms is the acceleration of physical and chemical decay of the rock, often accompanied by the formation of secondary minerals such as poorly-ordered aluminosilicates and clays (Cockell 2011). Nutrient release and mineral weathering abilities of bacteria vary between species (Wu et al, 2017)
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