Peran bakteri Rhizosfer terhadap detoksifikasi merkuri pada persemaian Calotropis gigantea L

PRASETYAWATI, Endang Triwahyu, Prof.Dr. Endang Sutariningsih, M.Sc

2005 | Tesis | S2 Biologi

Sebagian besar bakteri ditemukan di rhizosfer daripada di tanah. Beberapa bakteri berasosiasi dengan tanaman tertentu yang telah dikenal, khususnya sebagai organisme yang mendetoksifikasi logam berat. Tujuan penelitian ini untuk mempelajari macam bakteri rhizosfer yang mampu menghandel merkuri organik. Sebagai model tanaman dan sumber bakterinya untuk penelitian digunakan Calotropis gigantea dan rhizosfernya. Penelitian ini dimulai dengan mengisolasi bakteri dari tanah rhizosfer C. gigantea yang tumbuh di sekitar badan sungai, Sungai Sangon. Isolasi bakteri melalui tehnik kultur diperkaya dengan menggunakan medium cair basal yang mengandung HgCl2. Tiga tipe isolat dengan kecepatan pertumbuhan spesifik yang terendah, sedang dan tertinggi diseleksi untuk penelitian selanjutnya. Untuk mengetahui apakah isolat yang diseleksi itu berasosiasi dengan akar C. gigantea dalam mereduksi merkuri, tiga tipe isolat diinokulasi pada biji atau bibit melalui percobaan pertumbuhan tanaman. Bakteri yang terseleksi, selanjutnya diseleksi berdasarkan aktifitasnya yang mempengaruhi perkembangan tumbuhan. Pertumbuhan dan responnya terhadap HgCl2 diukur absorbansinya dengan spektrofotometer dan menggunakan CVAAS (Cold Vapour Absorbtion Atomic Spectrometry) at 353 nm. Hasil penelitian menunjukkan 15 bakteri rhizosfer berhasil diisolasi yang mampu tumbuh pada HgCl2, hanya 5 type bakteri yang resisten pada berbagai konsentrasi HgCl2. Percobaan kultivasi membuktikan hanya tiga isolat bakteri mampu mereduksi merkuri dengan mensintesis enzim spesifik dengan berat molekul 59 – 62 kDa pada gel poliakrilamid elektogram. Protein tersebut diduga merkuri reduktase. Tiga isolat tersebut diidentifikasi sebagai Baciilus strain BRH-8, Bacillus strain BRH-11, dan Pseudomonas strain BRH-12 yang mampu tumbuh pada medium Mac Conkey dengan membentuk koloni jernih dan pada medium Cetrimade Agar menghasilkan koloni berpigmen hijau.

Very frequently more bacteria are found in the rhizosphere than in soil. Several bacteria that are commonly associated with certain plants have been recoqnized especially as heavy metal detoxifying organism. The objective of the research was to study the diversity of rhizosphere bacteria capable of utilizing anorganic mercury (HgCl2). Calotropis gigantean L. and its rhizosphere were used as a model plant and the source of bacteria for the research, respectively The research was commenced by isolating bacteria from soil of rhizosphere’s C. gigantea grown around river bank of Sangon river. Isolation of the bacteria was carried out through enrichment culture techniques using liquid basal medium containing HgCl2. The bacterial isolates were selected based on their growth ability on medium containing HgCl2. Three type isolates with lowest, moderate and the highest spesific growth rate (μ) were selected for further observation. In order to know whether these selected isolates were associated with C. gigantea roots on reducing of among mercury toxicity, three isolates were inoculated on its seeds or its seedling through plant growth experiments. The selected bacteria were further selected based on their activities affected the plant growth. The latest selected bacteria were used for cultivation experiments. Their growth and their responses on HgCl2 were measured spectrophotometrical at absorbances of 600 nm and using CVAAS (Cold Vapour Absorbtion Atomic Spectrometry) at 353 nm. The research results revealed that fiveteen rhizosphere bacteria were able to grow on HgCl2 were successfully isolated, only five types of wwere reistaance on certain concentration of HgCl2. Based on their effect on seeds and plant growth, only three of five selected bacteria were used for detoxifying experiment. Those three selected bacteria demonstrated their ability to utilize HgCl2 by releasing specific enzymes with molecular weight of 59 – 62 kDa on poly acrylamide gel electrogram. They were assumed as three isolates were identified as Bacillus sp. Strain BRH-8, Bacillus sp. Strain BRH-11 and Pseudomonas sp. Strain BRH-12 with tipical clear colony grown on Mac Conkey medium and agreen colony on Cetrimade Agar medium.

Kata Kunci : Detoksifikasi Merkuri,Bakteri Rhizosfer,Persemaian, Detoxification, mercury (HgCl2), C. gigantea, AAS, Page-SDS