The accumulation of nitrogen (-N) is a serious problem in aquaculture as it could lead to mass mortality events of the cultivated species. Chemilitotrophic nitrification is the most recognized in nitrogen removal underestimating the role of heterotrophic nitrifiers. In the present study, the heterotrophic nitrification capacity of 8 bacterial strains isolated from mangrove soil, periphyton and biofilters was evaluated. The strains were grown in heterotrophic nitrification base medium (HNM medium) with three different nitrogen sources, ammonium, nitrite or nitrate at a final concentration of 8 mg L -1 , 5 mg L -1 and 80 mg L -1 respectively. The concentration of nitrogen (-N) and OD (600 nm) were determined periodically. Only in 4 strains belonging to the Bacillus genus was the capacity for heterotrophic nitrification and aerobic denitrification observed. Among these strains, SM4 strain presented a good removal profile of ammonium, nitrite and nitrate, achieving an average nitrification efficiency of 98. 33 ± 2.89%, 83.67 ± 7.51% and 98.00 ± 0.01% respectively, and a nitrification rate (mg L -1 h -1 ) of 1.71 ± 0.70, 0.13 ± 0.07 and 0.21 ± 0.06 respectively. The nxrB, nirS, nirK genes in the selected strains were identified by PCR. Additionally, several proteins (enzymes) involved in the nitrogen cycle were identified by proteomic analysis, reporting for the first time the presence of the enzymes ammonia monoxygenase (AMO) and nitrite oxide reductase (NXR) in the genus Bacillus. These findings suggest that the strains studied would have a potential use in the biological removal of nitrogen in aquaculture systems.
Se evaluó el efecto de seis soluciones crioprotectoras basadas en MgCl2 y metanol, acompañado de sucrosa y gel de Aloe vera al 10% o yema de huevo al 10%, sobre la viabilidad espermática en espermatóforo y masa espermática de Litopenaeus vannamei. Además, se usaron tasas de enfriamiento de -0.5, -1 y -2°C/min hasta lograr descensos de temperatura a -35, -80 y -100 °C previo a la inmersión en nitrógeno líquido. La tasa de viabilidad espermática fue determinada mediante la tinción eosina-nigrosina. Los resultados mostraron que las soluciones basadas en MgCl2, sucrosa más yema de huevo o gel de Aloe vera preservaron mejor la viabilidad espermática en espermatóforo (82.8 ± 2.3% y 72.6 ± 3.1%) y en masa espermática (83.4 ± 2.5% y 76 ± 1.1%), sin diferencias significativas con el grupo control (p>0.05). La curva de congelamiento que mostró menor daño en espermatóforo inició desde 25 °C y llegó a -35 °C con una tasa de -1 °C/min empleando una solución crioprotectora con yema de huevo y MgCl2, mostrando una viabilidad espermática mayor a 80% sin diferencias significativas con el grupo control (p>0.05), y una tasa de -2 °C/min en el mismo rango de temperaturas para el grupo con masa espermática y una solución basada en gel de Aloe vera. En conclusión, el uso de una solución compuesta por MgCl2, sucrosa, gel de Aloe vera o yema de huevo y una tasa de enfriamiento de -1°C/min o -2°C/min hasta alcanzar -35°C permite un exitoso congelamiento de espermatóforos o masa espermática de Litopenaeus vannamei.
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