الفهرس 
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Abstract
The feasibility of Bacillus subtilis application on immune, growth, and stress responses in Litopeneaus vannmei has been assessed before and after Vibrio parahemolyticus bacterial challenge by evaluating changes over time of some immune, growth, and stress-related gene expression; prophenoloxidase, serine proteinase, transglutaminase, lysozyme; and superoxide dismutase, Toll receptor, Penaeidin4 (immuno-related genes), Heat shock protein 70 (Lvhsp70) and Heat shock protein 90 (Lvhsp90) (stress related genes), Protein kinase C delta type (PKC) and Ras-related protein Rap-2a (Rap-2a) (growth related genes) . A total of 315 L. vannamei weighted 0.78 g ± 0.08 (SE) devided to 3 experimental groups, each group consisted of 3 replicates. Frist group (T1) was considered as a control, second group (T2) fed B. subtilis supplemented diet (2×109 CFU/kg feed) daily throughout the experiment. In contrast, the third group (T3) fed B. subtilis supplemented diet (2×109 CFU/kg feed) for a week followed by a week of basal diet alternatively. The findings before bacterial challenge manifested that proPO of (T2) expressed significantly in 1st, 2nd, 4th, and 7th weeks, while proPO of (T3) showed significant expression in 2nd and 7th weeks. In (T2) SP expressed highly in the 2nd and 7 th week. SP, TGase, and LYZ of (T3) presented significant up-regulation in the 7th week. TGase of (T2) expressed in 4th and 7th weeks. LYZ of (T2) expression levels increased significantly in the 2nd, 4th, 7th, and 12th weeks. SOD of (T2) up-regulated in 2nd, 4th, and 7th week, while (T3) SOD expression levels increased significantly in 4th and 7th weeks. In response to induced infection, proPO of (T2) up-regulated significantly at 3 and 24 (hpi), while SP expression levels of the same group increased insignificantly at 24 (hpi). Furthermore, TGase, LYZ, and SOD levels of expression of (T2) showed insignificant differences (p>0.05) from that of control. On the other hand, an obvious increase in (T3) proPO, SP, and SOD expression levels was observed to respond to bacterial infection at early and late infection phases 3 and 24 (hpi). However, the up-regulation response of LYZ and TGase expression levels of (T3) in response to induced infection was detected at late infection phase 24 (hpi). Also, it was showed that down-regulation of LvToll, HSP70, and HSP90 expression levels was predominant in (T3) and transient up-regulation of PEN4, PKC, and RAP-2a levels expression in the same group in 1st and 7 th week in which B. subtilis was supplemented. On the other hand, T2 II showed up-regulation of lvToll and HSP70 in the 2nd and 12th weeks of trial, PEN4 in 1st, 2nd, and 7th weeks, HSP90 7th and 12th weeks upregulation of PKC and PAP-2a was observed nearly upon the entire experimental period. Immune response against V. parahemolyticus was on guard in (T3) than (T2) as PEN4 expression levels of (T2) showing insignificant differences with that of control despite LvToll upregulation at the same time. LvToll, PEN4, HSP70, HSP90, and PKC (T3) showed rapid upregulation in response to induced bacterial infection. Simultaneously, HSP90 and PKC (T2) did not show any significant differences relative to control expression levels. Besides, HSP70 levels of the same group upregulated during the mid-infection phase and failed to be maintained in the late infection phase. RAP-2a responds to the bacterial challenge by significant down-regulation in both groups. This study suggests that the transient, weekly application of probiotic B. subtilis to shrimp may enhance the immune status, improve host stress tolerance, modulate pro-inflammatory responses, and trigger growth associated responses of shrimp.