دانلود رایگان مقاله جذب یون کلسیم با پروتئین خارج سلولی باکتری های گرمادوست

Abstract

The scaling of geothermal wells arising from formation of calcium carbonate is one of the major problems associated with the utilization of geothermal energy. A novel eco-friendly biological-based approach for geothermal well descaling was proposed. Thermophilic bacterial strains were isolated from geothermal areas in Taiwan and were evaluated for their calcium adsorption efficiency under the extreme conditions. Among the eight strains isolated, Tepidimonas fonticaldi AT-A2 isolated from Antun Hot Spring, Hualien showed the highest calcium adsorption capacity. The calcium adsorbing activity of T. fonticaldi AT-A2 was mainly associated with the extracellular proteins and the maximum calcium adsorption capacity (1.94 g Ca/g protein) was obtained at pH 10, 150 °C and 1 atm pressure. This calcium adsorption efficiency is much higher than that of metallothioneins and other bacterial extracellular proteins. The excellent calcium adsorption efficiency of the AT-A2 proteins indicates the potential for their applications in biological geothermal well descaling.

3. Results and discussion

3.1. Isolation and identification of calcium adsorbing bacteria originating from geothermal sites Eight thermophilic bacterial strains, capable of producing calcium adsorbing extracellular proteins, were isolated from five geothermal areas of Taiwan, including Tatun volcanic area in Taipei City, Chingshui and Renze geothermal areas in Yilan County, Antun geothermal area in Hualien County, and Chinlun geothermal area in Taitung County. The strains were cultured on Tryptic Soy Broth (TSB) medium and re-plated on TSB agar plates to obtain pure cultures. All strains grew well at 55 ◦C on 5-fold dilution TSB medium under aerobic conditions. The cultures were designated as IC-5, YM, BE-A1, BE-C, LJ-B, GL, AT-A1, AT-A2 for identification purposes. The bacterial strains were identified by 16S rDNAsequencing and the highest similarity for each sequence was determined. As per the similarity values obtained, the strains were named as follows: Anoxybacillus kamchatkensis IC-5 (98.7% similarity), Thermus scotoductus YM (99.7% similarity), Mycobacterium hassiacum BE-A1 (100% similarity), Brevibacillus thermoruber BE-C (99.5% similarity), Anoxybacillus mongoliensis LJ-B (98.9% similarity), Bacillus halodurans GL (99.9% similarity), Meiothermus ruber AT-A1 (100% similarity), Tepidimonas thermarum AT-A2 (100% similarity). The 16 rDNA phylogenic analysis of the eight strains is depicted in Fig. 1. A further analysis was done to clarify the taxonomic position of Tepidimonas thermarum AT-A2 by a polyphasic taxonomic approach and was reassigned as a novel species Tepidimonas fonticaldi sp. nov. type strain AT-A2, with a NCBI Genbank accession number of JN713899 [27]. The 16S r DNA sequence of strain AT-A2 is shown in Fig. S1.