Characterization and functional analysis of nifH encoding Nitrogen fixation bacteria in Nile Tilapia pond sediment

Abstract

Kamira Barry, Fan Li Min, Shun long Meng, Song Chao, Chen Jia Zhang

In this study, an investigation was carried out on bacterial communities involved in nitrogen fixation in three different intensity Nile tilapia (Oreochromis niloticus) culture ponds. Summer physicochemical factors defining the sediment degradation were determined. Results revealed that pond temperatures ranged from 27.3 to 34.2ºC, dissolved oxygen 6.31 to 8.99 mg/L and pH was between 7.18 and 7.98. Nutrient levels differed significantly (P < 0.05) amongst the ponds: Total phosphorous values in the ponds were 0.034, 0.038 and 0.028 % while total organic carbon values (P < 0.05) were 4.33, 4.93 and 4.16 mg/Kg for the three ponds respectively. There were no significant differences (P<0.05) in total nitrogen and nitrite nitrogen registered throughout the study. The nitrogen fixation microbial communities presumed to significantly reduce pond nitrification were taxonomically identified to their most probable genera that included; Bradyrhizobium, Magnetospirillum, Rhodomicrobium, Rhodospirillum Sinorhizobium, Azotobacter, Methylobacter, Methylomonas, Thiocapsa, Geobacter, Anaeromyxobacter, Desulfobacca, Desulfobulbus, Desulfomicrobium, Desulfovibrio and Syntrophobacter genera. The quantitative analysis revealed the nifH gene mean abundances were 3.02 x 107 , 4.06 x 107 and 4.85 x 107 copies/g wet weights in ponds 1, 2 and 3 respectively. The Redundancy analysis indicated that total phosphorous and total organic carbon were the most important factors in shaping the bacterial communities while stocking densities of 1,800 or less fish per 667 sq. M were not regulating factors for the microbial abundances. This study would set stage for future investigations on enzymatic catalysis and oxidative roles of the identified microbe communities to species level, for wide adoption in cultures.