Kemampuan Konsorsium Bacillus pada Pupuk Hayati dalam Memfiksasi N2, Melarutkan Fosfat dan Mensintesis Fitohormon Indole 3-Acetic-Acid
Abstract
Abstrak. Bakteri Bacillus sp. non patogenik memiliki potensi sebagai pupuk hayati. Pupuk hayati di Indonesia sebagian besar terdiri atas konsorsium beberapa macam mikroba. Pupuk hayati yang diuji, “Pupuk X†terdiri atas 10 spesies bakteri Bacillus sp. Penelitian ini bertujuan untuk mengevaluasi efektivitas Pupuk X dalam melarutkan fosfat, memfiksasi N2 dan mensintesis fitohormon Indole-3-Acetic Acid (IAA), serta mengujinya secara in planta pada bibit padi. Kemampuan melarutkan fosfat diuji pada media Pikovskaya padat dengan mengamati munculnya zona bening di sekeliling koloni. Kemampuan memfiksasi N2 secara kualitatif dan kuantitif masing-masing diuji pada media NFB padat dan Acetylene Reduction Assay. Kemampuan sintesis IAA diukur secara kolorimetri pada λ 530 nm, sedangkan pengaruh pupuk hayati cair terhadap bibit tanaman padi diuji secara in planta menggunakan bibit padi varietas IPB3S. Sedikitnya terdapat enam spesies bakteri Bacillus pada pupuk hayati yang digunakan memperlihatkan morfologi koloni berbeda, dengan total populasi mencapai 7,6Ãâ€â€Â1011 cfu ml-1 dan ukuran sel-sel Bacillus sp. bervariasi antara 2,39-3,01 µm. Pada pupuk hayati ini terdeteksi aktivitas nitrogenase sebesar 0,05685 µm ml-1 jam-1. Konsorsium Bacillus ini dapat melarutkan fosfat dari sumber Ca3(PO4)2 dengan indeks pelarut fosfat 2,6. Fosfat terlarut tersebut disebabkan karena produksi empat jenis asam organik oleh Bacillus sp., yaitu asam asetat, asam oksalat, asam laktat, dan asam malat dengan konsentrasi sekitar 0,01-1,02 mg l-1. Konsentrasi IAA pada pupuk hayati cair terdeteksi sebesar 3,0065 µg ml-1. Inokulasi Pupuk X pada bibit padi dapat meningkatkan jumlah akar lateral 42,8% yang berpotensi meningkatkan serapan hara dalam tanah.
Abstract. Non-pathogenic Bacillus sp. has the potential as a biofertilizer. Biofertilizers in Indonesia mostly consist of a consortium of several kinds of microbes. Liquid biofertilizer, “Biofertilizer X†is a compound fertilizer consists of ten species of Bacillus sp. This research was aimed at evaluating the ability of the Bacillus consortium in Biofertilizer X to dissolve phosphate, fix N2 and synthesize Indole-3-Acetic Acid (IAA) phytohormone, as well as its effect on rice seedling. The ability to dissolve phosphate was tested on solid Pikovskaya media by observing the appearance of a clear zone around the bacterial colony. The ability to fix N2 qualitatively and quantitatively was tested on solid NFB media and Acetylene Reduction Assay, respectively. The ability of IAA synthesis was measured by colorimetry at λ 530 nm, while the effect of liquid biofertilizers on rice seedlings was tested in planta using IPB3S variety rice seedling. There were at least six species of Bacillus in liquid biofertilizers showing different colony morphologies. The total population reached 7.6 Ã 1011 cfu ml-1 and the size of Bacillus sp. varied between 2.39-3.01 µm. Nitrogenase activity of this biofertilizer was detected at 0.05685 µm ml-1 h-1. This Bacillus consortium solubilized  phosphate from Ca3(PO4)2 source with solubilizing index of 2.6. This solubilization was attributable to the  the production of four types of organic acids by Bacillus sp., namely acetic acid, oxalic acid, lactic acid, and malic acid with concentrations of 0.01-1.02 mg mg l-1. IAA concentrations in this  biofertilizers were detected at 3.0065 µg ml-1. Inoculation of this biofertilizers increased the number of lateral roots of rice seedlings by 42.8% and these lateral roots have the potential to increase nutrient uptake in the soil.
