| Investigations to identify characterize and define microbial communities involved in nitrogen fixation within the water columns,and soil sediment structures were carried out in three different intensity monoculture and polyculture tilapia(Oreochromis sp)research pond facilities during a summer production of 2014 in Yi Xing Jiangsu China.These microbes offer biological mechanisms that significantly eludes pond fertilizer usage resulting in reduction or elimination of nitrate leaching or pollution in aquaculture facilities yet vividly known to promote plant growth.Opting for the biological methods to boost fish production,to improve on the water quality we focus on obtaining information on the environmental effects to the identified,characterized and defined microbes known to also promote plant(vegetable)growth alongside the fish production.Parallel microbial identification by illumina high through-put sequencing and quantitative polymerase chain reaction methods for environmental bacterial distribution assessments were used in identifying the total bacterial population basing on gene probing DNA sequences.The microbial communities in ponds 1 and 2(monoculture system)and pond 3(polyculture system)that encoded the nifH-gene yet known for promoting plant growth,were taxonomically identified to their most probable genera revealing Azospirillum,Azoarcus,Anaeromyxobacter,Azotobacter,Geobacter,Rhodomicrobium,Desulfobacca,Desulfobulbus,Desulfovibrion,Methylomonas,Thiocapsa and unclassified_Opitutaceae as the most dominant among others.The summer physiochemical factors defining the pond degradation were determined and correlated with different pond microbial communities to ascertain the environmental influences on the survival and existence of the nitrogen fixers.The monthly mean temperature ranges(27.3 to 34.2?),dissolved oxygen(6.31 to 8.99 mg/L and pH(7.18 to 7.98)values as documented were observed to be above pond culture optimal.The nutrient levels differed significantly(P<0.05)amongst the ponds,and of the studied environmental factors,ammonium nitrogen observed to have the greatest influence on the communities recorded the highest significant differences within the water column microbes i.e.3.18,1.98 and 3.41 mg/L for the studied ponds 1,2 and 3 respectively.The chemical oxygen demand(P<0.05)within the respective water columns i.e.14.06,14.28 and 12.16 mg/L;and the total organic carbon(P<0.05)within the soil sediment i.e.4.33,4.93 and 4.16 mg/Kg for ponds 1,2 and 3 revealed that there was an increment in energy sources within the pond systems.The resultant quantitative analyses of the microbes encoding nifH-gene in the sediment soils abundances were established as 3.02 x 107,4.06 x 107 and 4.85 x 107 copies/g wet weights in ponds 1,2 and 3;while the water column microbial abundances were established as 3.65 x 10~6,2.66 x 10~6 and 3.11 x 10~6 copies/g wet weights(ww)for the same ponds.An in-depth study of linear discriminant analysis(LDA)effect size(LEfSe)with a particular focus on metagenomic analyses resulted in high dimensional class comparisons in the sediment and soil microbes with 19,17 and 11 clades in ponds 1,2 and 3 respectively while in the water column it revealed Chromatiaceae especially genus Thiocapsa had the closest relatives in all the three ponds.The Redundancy analysis(RDA)test,in the sediment soil microbial communities indicated that total phosphorous and organic matter were the most important factors in shaping the bacterial communities;on the contrary within the water column the test indicated ammonia nitrogen,total phosphorous and dissolved oxygen were the most important factors shaping the bacterial communities.From the study results it was evident that stocking density of 1,800 or less fish per 667 sq.M were not limiting factors associated with regulating the abundance of nifH-encoding nitrifiers.These studies further set stage for future investigation on enzymatic catalysis and oxidative part of the identified microbes to species levels,for their wider adoption for culture. |
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