Bdellovibrio and like organisms promoted growth and survival of juvenile abalone Haliotis discus hannai Ino and modulated bacterial community structures in its gut

BALOs Improved Gut Microbiota Health in Postlarval Shrimp (Litopenaeus vannamei) After Being Subjected to Salinity Reduction Treatment

“…Nevertheless, contrary to Zheng et al (2017), who stated that "bacterial community change in the rearing water only have limited influence on intestine of shrimp larvae, " here our data clearly showed that addition of BDN-1F2 to waters at the start hugely impacted PL gut microbiota, both compositionally (Tables 6-9, Supplementary Tables S4, S5, Figures 1, 2, and Supplementary Figure S2) and functionally ( Table 10, Supplementary Tables S2, S3, Figures 3, 4, and Supplementary Figure S3), exceedingly enhanced their biodiversities and strengthened their functionalities. A similar finding, at least compositionally, was demonstrated by Guo et al (2017), who showed that, at the end of the 90-day test, bacterial communities in abalone guts in test had a higher Shannon diversity index (H') and Pielou's evenness index (J') and a slightly lower richness value (Rs) when compared to control. Moreover, 16S rDNA-PCR and denaturing gradient gel electrophoresis profiles revealed that, of the 27 species/strains sequenced, 51.85% were shared by both control and test and 22.22% reduced, of which 33.33% were Vibrio.…”

“…With regards to the mechanism(s) of BALOs exerted on PL gut microbiota, different from the currently existing concept that predatory bacteria prey on the dominant species and, thus, restore the microbial biodiversity in a community but with no further elaborations (e.g., Xiong et al, 2017 ; Johnke et al, 2019 ), we here envisage a more elaborate conceptual mechanism on the basis of this study and of Guo et al (2017) ; that is, after the introduction of a BALO into a microbial community, it should first attack some of its susceptible microbes on its way, be it dominant or not (of course the BALO would have more chances to meet a dominant at the start, but if the dominant is not to its liking, BALO may not lyse it at all). After a few rounds of multiplication, the BALO has created some space/new niches in the community for some of the preexisting microbes, and, in turn, these microbes, especially those potentially beneficial microbes, would start to grow.…”

“…This would leave 0.02% in relative abundance for other unclassified BALOs, which implies that BDN-1F2 in the PL gut microbiota would not exceed this figure in abundance even if present. This very few or non-presence of BDN-1F2 in PL guts is in line with the findings of Shatzkes et al (2017) , who were “unable conclusively to detect B. bacteriovorus in fecal samples after intrarectally introducing predatory bacteria into the rat gastrointestinal tract,” and of Atterbury et al (2011) , who were “also not able to detect B. bacteriovorus in the fecal and cecal contents of young chicks after oral administration of predatory bacteria, signaling that exogenous B. bacteriovorus introduced into the gut environment may be short-lived.” Additionally, a study carried out by Guo et al (2017) also showed that no BDH12 was detected in abalone integer/gut samples even though a concentration of ca. 1 × 10 5 PFU mL –1 was added weekly.…”

“…Similar findings of bacteria reduction by BALOs in aquaculture have also been reported. For example, Guo et al (2016) applied BALO strain BDW03 in the rearing of juvenile turbot and revealed that TCBC and TCVC in both waters and intestines were significantly reduced compared to control; Guo et al (2017) applied BALO strain BDH12 in cold water abalone (Haliotis discus hannai Ino) juvenile rearing and showed that, compared to control, TCVC and TCBC in test were reduced by 2.39 and 4.07 log CFU•mL −1 , respectively, in rearing water (p < 0.05), and by 3.54 and 4.11 log CFU•g −1 , respectively, in abalone guts (p < 0.05). Li et al (2014) also reported that, by adding BALO strain BDHSH06 to the rearing waters of black tiger shrimp (Penaeus monodon) over an 85-day period, TCBC and TCVC were significantly reduced (p < 0.05) by 1.3 to 4.5 log CFU mL −1 and CFU g −1 in both water and shrimp intestines, respectively, compared to control.…”

“…As gut microbiota in each individual farmed organism varies, a practice is to pool them together so as to avoid individual variations (Vadstein et al, 2013;Guo et al, 2017). Especially due to the salinity reduction treatment, the quantity of gut microbes in PL had been hugely reduced (as shown by the plate counts, 2-5 log CFU mg −1 , Table 2), and initial PCR amplifications on individual replicate failed.…”