Experimental optimisation of various cultural conditions on urease activity for isolated Sporosarcina pasteurii strains and evaluation of their biocement potentials

Abstract

Microbially induced carbonate precipitation (MICP) is a process that has emerged as an attractive alternative ground improvement technique in Geotechnical and Civil Engineering using ureolytic bacteria for soil strengthening and stabilisation. Locally isolated Sporosarcina pasteurii from limestone cave samples of Sarawak were found to have high urease-producing abilities. Optimisation of various cultural conditions (incubation temperature, initial pH medium, incubation period and urea concentration) were performed using conductivity and optical density measurements to determine the maximum specific urease activity. In addition, an in vitro biocement test was done to define the prospect of using these bacterial isolates in civil engineering work for the improvement of soils with inferior properties. The experimental results showed that urease activities were optimum at 25 to 30°C, pH 6.5 to 8.0, 24 hr incubation and 6 to 8% (w/v) urea concentration. It was also demonstrated that biocementation using the local ureolytic bacteria can improve the strength of poorly graded soils. However, the efficiency of the MICP process in improving the soil's strength varied among samples treated with different bacterial cultures.

Feasibility study for slope soil stabilization by microbial induced carbonate precipitation (MICP) using indigenous bacteria isolated from cold subarctic region

“…Lysinibacillus xylanilyticus reported in this paper showed the highest activity at weak alkali conditions. Similar phenomena could be seen on certain microbial urease like Sporosarcina pasteurii [23,40], Pararhodobacter sp. [27] and Klebsiella aerogenes [44], those have the optimum activity under weak alkaline conditions.…”

“…Numerous investigators have studied the effect of temperature on the rate of urea hydrolysis of many soil bacteria [23,27,30,40]. In general, their results have indicated that the rate of urea hydrolysis increases with increasing temperature, suggesting that the urease of most of the soil bacteria is not heat inactivated (up to the temperature ranging 45-60 °C).…”

“…Temperature and pH are the most governing factors of activity of bacterial urease [23]. Urease activities under different temperatures (10-50 °C) are provided in Fig.…”

“…The enzymes of the bacteria are thermal sensitive and can readily be denatured by even a slight change of environmental temperature [22]. Most of the MICP studies have employed Sporosarcina pasteurrii for urea hydrolysis due to the highly active urease enzyme [5,6,11,13,[23][24][25]. Only a few MICP studies focused on introducing some other ureolytic strains including Bacillus sphaercus (MCP-11) [26], Pararhodobactor sp.…”

Assessing ureolytic bacteria with calcifying abilities isolated from limestone caves for biocalcification

“…The conductivity values were recorded and used to plot the gradient (mS cm ‐1 min ‐1 ) before being converted to urease activity (mol urea hydrolysed per minute) with regard to the dilution factor (Omoregie et al . ). A calibration curve was previously performed by Whiffin () under standard condition at 25°C with purified urease (Sigma Cat.…”