Nitrogen Fixing Bacteria Lab Report

Effect of different physical conditions on nitrogen fixing bacteria from rhizosphere

Hypothesis:

Rhizospheric Nitrogen fixing bacteria show optimal growth at PH: 6-7, Temperature: 30 °C and Salinity level: 0.005 – 0.010M NaCl

INTRODUCTION: There is a huge bacterial diversity in rhizospheric soil. Gram-negative, non-sporulating baccilli which respond to root exudates are predominant in the rhizosphere (Pseudomonas, Agrobacterium). While Gram-positive bacilli, Cocci and aerobic spore forming bacteria like Bacillus and Clostridium are rare in the rhizosphere. The most common genera of bacteria are Pseudomonas, Arthrobacterm Mycobacterium, Flavobacter, Cellulomonas, Agrobacterium, Alcaligenes, Azotobacter,

We took 2 Petri plates containing L-agar and spread 50µl from dilutions 〖10〗^(-3) and 〖10〗^(-5) respectively on L-agar plates by using spreader and incubated them at 37°C for 24 hours. After 24 hours incubation, we selected isolated colony and streak it on L-agar containingPetri plates to purify it.

After 24 hours incubation, we got our purified colony, now we checked either it is nitrogen fixing bacteria or not, for this purpose we performed “Nitrite Detection Test”.

Nitrite Detection Test: We made mother culture of our strain. We took 3 test tubes and added 3 ml ammonium sulphate broth and autoclaved them. Then labelled them as +ve control, -ve control and test. In +ve control, we added 0.1 gram soil, in –ve control,we didn’t add anything and in 3rd test tube we added 0.1ml from mother culture. We incubated all of them at 37°C for 7 days. We took slide and divided it into 3 portions and labelled as +ve, -ve and test. And placed one drop from each test tube on slide. Now added one drop of Trommosdrof reagent on each three sites and checked results.

Interpretation:

No color -------- -ve