Diversity of Free-Living Nitrogen Fixing Bacteria on Recent Volcanic Deposits of Mt. Merapi

ANNISA NUR LATHIFAH, Prof. Dr. Irfan D. Prijambada ; Prof. Dr. Hiroyuki Ohta

2015 | Tesis | S2 Bioteknologi

Substrat baru yang terbentuk akibat letusan gunung berapi seperti lava, tephra, dan abu vulkanik memiliki kandungan carbon dan nitrogen dalam jumlah yang sangat kecil. Pasokan elemen-elemen tersebut tergantung pada deposisi basah dan / atau kering dan juga aktivitas fiksasi N2 dan CO2 oleh komunitas mikroba awal terutama bakteri penambat karbon dan penambat nitrogen. Penelitian ini mempelajari bakteri penambat nitrogen pada deposit vulkanik Gunung Merapi. Bakteri penambat nitrogen bebas telah diisolasi menggunakan medium spesifik yaitu medium 10x Diluted R2A dengan metode direct plating. Sebanyak 128 isolat diklasifikasikan ke dalam 105 kelompok dengan metode Repetitive PCR dan strain dengan profil unik diidentifikasi berdasarkan urutan gen 16S rRNA sebagai Proteobacteria, Firmicutes, Actinobacteria, atau Bacteroidetes. Semua isolat tumbuh pada media bebas nitrogen dan beberapa isolat (isolat BR28, BR 38, BR 47, BRU I 1, I BRU 21, BRU 12, BRU 25, FR 3, FR 4, FR 31) memiliki gen nifH . Isolat tersebut termasuk ke dalam genera Bradyrhizobium, Novosphingobium, Ralstonia, Arthrobacter, Rhizobacter, Dyella, Tetraspahera, Lysinibacillus, dan Bacillus.

Newly emplaced substrate by volcanic eruption such as lava, tephra, and volcanic ash contain negligible amount of organic matter and fixed nitrogen. Supply of these elements depends on the wet and/or dry deposition and also the activity of N2 and CO2 fixation by the early microbial community particularly carbon fixing bacteria and nitrogen fixing bacteria. In the current study, we investigated nitrogen fixing bacteria in recent volcanic deposits of Mt. Merapi. The free-living diazotrophs have been isolated using 10-fold diluted R2A medium by direct plating method. A total of 128 isolates were classified into 105 groups by their genomic fingerprinting patterns, and strains with unique profiles were identified on the basis of sequencing of their 16S rRNA genes as Proteobacteria, Firmicutes, Actinobacteria, or Bacteroidetes. All isolates grew on the nitrogen-free medium and some of them (isolates BR28, BR 38, BR 47, BRU I 1, BRU I 21, BRU 12, BRU 25, FR 3, FR 4, FR 31) possessed the nifH gene. These isolates belonged to genera Bradyrhizobium, Novosphingobium, Ralstonia, Arthrobacter, Rhizobacter, Dyella, Tetraspahera, Lysinibacillus, and Bacillus.

Kata Kunci : Volcanic deposit, N2-fixation, Mt. Merapi, nifH gene