Microbial producer of acid urease for its application in biocementation.

Introduction. A popular biocementation method, microbially initiated precipitation of calcium carbonate, is accompanied by the release of ammonia and ammonium ions into the environment. The aim of the present study was selection of a producer of acid urease for its application in biocementation based on the calcium phosphate formation. Materials and methods. Isolation, selection, identification, and characteristics of bacterial producer of acid-tolerant urease were conducted. Sequencing the 16S rRNA gene of isolate was done for its identification. Bone meal served as a source of calcium for biocementation using inactivated cells of bacterial producer of acidtolerant urease. Assessment of sand biocementation was provided by the change of its water permeability. Results and discussion. Selection of a bacterial strain that synthesized acid urease was carried out among bacteria isolated from acidic soil. The strain with the highest urease activity was identified by rRNA gene amplification and sequencing as Staphylococcus saprophyticus AU1. The physiological properties of the strain were studied. The maximum growth rate of strain AU1 was 0.15 h-1, the maximum accumulation of biomass was 6.9 g/l of dry biomass, and the maximum urease activity was 8.1 mM hydrolyzed urea/min. The highest urease activity of Staphylococcus saprophyticus AU1 was found in the pH range from 4.5 to 5.5, and it gradually decreased with pH increasing. To ensure environmental biosafety, the use of inactivated bacterial cells that retain urease activity has been proposed. To receive completely inactive cells, they were treated with 0.5% sodium dodecyl sulfate solution for 90 minutes. Biocementation of sand was conducted using inactivated cells of S. saprophyticus AU1 and acid hydrolysate of bone meal, which has calcium in the form of phosphorus-containing compounds. The water permeability of biocemented sand was 2·10-5 m/s, which makes it possible to use biocementation of this type to strengthen the soil to reduce its liquefaction, for example after an earthquake, or to control dust erosion for prevention of atmospheric pollution. Conclusions. The main advantage of the proposed method for biocementation is the diminishing of urea consumption up to 75% and, thereby, reduction of emissions of ammonium and ammonia into the environment. In addition, the problem of bone waste disposal is solved and the cost of materials for biocementation is reduced. [ABSTRACT FROM AUTHOR]