| Summary: | The research on phosphate solubilizing bacteria was carried out to understand the
role of the soil microbial community encompassing to mobilization activities of the
phosphate from the effect of changing physicochemical conditions caused by volcanic
eruption Mount Merapi. The study was focused on isolation of phosphate solubilizing
bacteria (PSB) and bacterial community structural analyses of soil as affected by volcanic
materials at sampling site. The soil and volcanic material were collected from Merapi areas
within interval of 1, 3, and 6 months. Hydrolytic activities of soil bacteria were detected with
fluorescein diacetat technique (FDA). Samples which were positively detected of FDA
method, were subsequently analysed for diversity of soil bacteria by using Denaturing Gel
Gradien Electrophoresis (DGGE). In addition, from the same sample, PSB were selectively
isolated by using Pikovskaya medium based on the clear zone index value. The selected
bacterial isolates were tested for their activities in solubilizing phosphate using different
phosphate (Ca-P and Al-P) and in producing auxin. Based on phosphate solubilizing and in
producing auxin, the isolates were subquently selected. There genetic characters as
biofertilizer agents were also determined by detecting 4 functional genes involved in
solubilizing phosphate, auxin production, nitrogen fixation, and nitrification. The selected
isolates were characterize molecularly based on 16S rRNA gene sequences. The results of the
study showed that community of soil bacteria on Merapi eruption-affected area was
susceptible to physicochemical of environment and it took 6 months for it recovery. A total
of 23 isolates of bacterial colonies were isolated and only 9 isolates which were able to
demonstrate solubilizing phosphate (Al-P) medium and or producing auxin of the isolates
namely BS1F, BS2K, BS3ML2, BS4ML4, BS6TM1, BS7TM2, BS14E601 and BS15E032.
The nine isolates were detected to have a variety of 4 functional genes and only BS2K was
found to have all the 4 functional gene. Based on 16S rRNA molecular analysis, the selected
isolates were identified to be member of genus Burkholderia (BS1F, BS2K, BS3ML2,
BS6TM1, BS7TM2), Enterobacter (BS14E601 & BS15EO32), Klebsiella (BS13E301) and
Bacillus (BS4ML4). Therefore, the phosphate solubilizing and auxin producing bacteria
could be obtained from samples collected from Mount Merapi eruption-affected area.
Furthemore, it was also observed bacterial comunity could only recovery require 6 months.
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