Disclosure of Invention
In order to solve the problems, the invention provides a mandarin fish source lactococcus lactis strain.
The Lactococcus lactis strain 3-c-18 has the preservation number of CGMCC No. 17347.
The lactococcus lactis strain 3-c-18 is obtained by separating and purifying the intestinal tracts of the mandarin fish.
The invention also provides a microecological preparation containing the lactococcus lactis strain 3-c-18.
In one embodiment of the invention, said probiotic comprises a fermentation broth of said lactococcus lactis.
Wherein the viable count of the lactococcus lactis is 1 multiplied by 10 8 CFU/mL~1×10 10 CFU/mL。
The invention also provides a feed containing the lactococcus lactis or the microecological preparation.
Wherein the viable count of lactococcus lactis in the feed is 1 × 10 5 CFU/g~1×10 7 CFU/g。
The invention also provides a fermentation method of the lactococcus lactis, which adopts a liquid fermentation culture medium consisting of: 2 percent of sucrose, 0.9 percent of peptone, 0.1 percent of yeast powder, 0.25 percent of NaCl, CaCO 3 0.1%,MgSO 4 ·7H 2 0.1 percent of O and 0.0625 percent of defoaming agent; fermentation conditions are as follows: natural pH, fermentation temperature of 35-38 ℃, rotation speed of 80-120 rpm, and aeration ratio of 1: 0.1 to 0.5vvm and a tank pressure of 0.03 to 0.07 MPa.
The invention also provides application of the lactococcus lactis or the microecological preparation in mandarin fish culture.
The invention also provides application of the lactococcus lactis in preparation of medicines for inhibiting aeromonas hydrophila, staphylococcus aureus and vibrio parahaemolyticus.
Specifically, the inhibitor for aeromonas hydrophila, staphylococcus aureus and vibrio parahaemolyticus is prepared by using the strain or the composite microecological preparation.
The Lactococcus lactis (Lactococcus lactis) strain 3-c-18 provided by the invention is preserved in the China general microbiological culture Collection center at 18 months 3 in 2019, and the address is as follows: the collection number of the microbial research institute of the Chinese academy of sciences, No. 3 Xilu-Beijing province, Chaoyang, and the collection number is: CGMCC No. 17347.
Compared with the prior art, the invention has the following advantages:
(1) the lactococcus lactis 3-c-18 has the characteristics of acid production, acid resistance, no hemolysis and the like, and in vitro experiments show that the lactococcus lactis 3-c-18 has an inhibiting effect on various aquatic pathogenic bacteria, has stronger antibacterial activity particularly on aeromonas hydrophila, staphylococcus aureus and vibrio parahaemolyticus, can be used as a substitute of an antibiotic growth promoter, and has good application prospect.
(2) The lactococcus lactis 3-c-18 is derived from the intestinal tracts of mandarin fishes, can obviously improve the health level of liver tissues of the mandarin fishes, improve the nutrient metabolism of the mandarin fishes, reduce the bait coefficient, effectively promote the growth of the mandarin fishes, and can be used as a feed mate to be applied to the mandarin fish culture.
(3) In culture, the lactococcus lactis 3-c-18 has a certain resistance effect on the infection of common aquatic harmful bacteria aeromonas hydrophila, and has a better application prospect.
Detailed Description
The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
EXAMPLE 1 screening of lactococcus lactis (L.lactis)3-c-18
1. Preliminary screening
Taking five mandarin fish from the mandarin fish culture pond, dissecting mandarin fish by aseptic technique, taking out intestinal content, mixing, and placing into freezing tube. Respectively weighing 5g of sample, adding 45ml of sterile Phosphate Buffer Solution (PBS), uniformly mixing to prepare bacterial suspension, diluting the bacterial suspension to a proper gradient by using the PBS, coating the gradient on a lactic acid bacteria culture Medium (MRS), and culturing to obtain 64 suspected lactic acid bacteria strains.
The 64 strains obtained were further isolated and purified on MRS medium.
Inoculating the separated and purified strains on a bromocresol purple lactose peptone (BCP) culture medium for culture, and observing the condition that the acid production phenomenon of the strains changes from purple to yellow, namely the strains to be selected.
The obtained candidate strain is inoculated on a hemolysis plate for culture, and the hemolysis phenomenon is observed. Strains without hemolysis were selected for further experiments.
The preparation method of the PBS buffer solution comprises the following steps: KH with the concentration of 0.1mol/L is respectively prepared 2 PO 4 And Na 2 HPO 4 ·2H 2 And (4) after all the O is dissolved, uniformly mixing in equal volume.
MRS liquid medium: 10g of peptone, 10g of beef extract, 5g of yeast extract and K 2 HPO 4 ·3H 2 O2 g, diammonium citrate 2g, sodium acetate 5g, glucose 20g, Tween 801 mL, MgSO 4 ·7H 2 O 0.58g,MnSO 4 ·H 2 O0.25 g, distilled water 1000mL, pH 6.4, 121 ℃ sterilization for 15 min.
MRS solid medium: 10g of peptone, 10g of beef extract, 5g of yeast extract and K 2 HPO 4 ·3H 2 O2 g, diammonium citrate 2g, sodium acetate 5g, glucose 20g, Tween 801 mL, MgSO 4 ·7H 2 O 0.58g,MnSO 4 ·H 2 0.25g of O, 20g of agar and 1000mL of distilled water, the pH value is 6.4, and the mixture is sterilized for 15min at 121 ℃.
BCP solid medium: 25g of yeast extract, 5g of peptone, 5g of lactose, 0.04g of bromocresol purple, 15g of agar, 1000mL of distilled water, pH 7.2 and sterilization at 115 ℃ for 30 min.
2. Double sieve
(1) Acid production capacity of candidate strain
Inoculating the seed liquid of the strain to be selected into an MRS liquid culture medium according to the amount of 1%, standing and culturing at 37 ℃, taking culture liquid at different time points, and measuring the pH value of the culture liquid. Selecting the strains which produce relatively fast acid and have more acid as the strains to be selected.
(2) Acid resistance of candidate strain
The seed liquid of the strain to be selected is inoculated into MRS liquid culture media with different pH values (6.5, 5.5, 4.5, 3.5, 2.5 and 1.5) according to the amount of 1 percent and cultured for 24 hours. During the culture, the OD values of the culture broth were measured at different time points. Selecting the strain with better acid resistance.
Experimental results show that the acid production performance of the lactococcus lactis 3-c-18 is good, and the pH of a culture solution is 4.3 when the lactococcus lactis is fermented for 72 hours. When the pH of the culture solution is higher than 4.5, the strain can grow normally and grows faster.
The viable count of the lactococcus lactis 3-c-18 bacterial liquid detected by a flat plate colony counting method is about 1 multiplied by 10 10 CFU/mL。
Photographs of the growth of lactococcus lactis 3-c-18(L.lactis) on medium plates are shown in FIG. 1.
EXAMPLE 2 bacteriostatic study of lactococcus lactis (L.lactis)3-c-18
Test strains: the strain lactococcus lactis 3-c-18 obtained by screening in example 1, MG1614 isolated from commercial MG1614 lactococcus lactis powder, and lactococcus lactis S6-2 preserved in a laboratory with the preservation number of CGMCC No. 9135.
And (3) indication bacteria: staphylococcus aureus, Vibrio haemolyticus, Escherichia coli, Aeromonas hydrophila, and Vibrio parahaemolyticus.
The test strains and the indicator strains are activated respectively.
A pure agar plate culture medium containing 2% agar and an LB soft plate culture medium containing 1% agar are prepared, respectively, and sterilized at 121 ℃ for 20 min.
After sterilization, the pure agar plate medium was removed, and the LB soft plate medium was incubated, and the plates were inverted to give about 10ml each. After the agar plate solidified, 5 sterilized oxford cups were placed evenly on the solidified plate. Taking out the LB soft plate culture medium, when the temperature is reduced to about 50 ℃, respectively adding 100 mu l of indicator bacterium liquid into the culture medium, uniformly mixing, and uniformly pouring into an agar plate with an oxford cup.
After the bacteriostatic plate solidified, the oxford cup was carefully pulled out with tweezers. The position to which the test strain was applied was marked on the plate, and 100. mu.l of a bacterial solution of the test strain was added to the well and cultured at 37 ℃ for about 24 hours. Observing the existence and the size of the inhibition zone, and recording. The results are shown in Table 1.
TABLE 1 diameter of lactococcus lactis zone of inhibition (unit: mm)
Note: -no significant zone of inhibition
The test result shows that: the lactococcus lactis 3-c-18 has stronger antibacterial activity on aeromonas hydrophila, staphylococcus aureus and vibrio parahaemolyticus, and the antibacterial effect is better than that of MG1614 and S6-2. Therefore, the strain is a strain which can selectively inhibit aeromonas hydrophila, staphylococcus aureus and vibrio parahaemolyticus.
EXAMPLE 3 fermentation and bacterial liquid preparation of lactococcus lactis (L.lactis)3-c-18
Fermentation of lactococcus lactis 3-c-18: the fermentation medium used is prepared as follows: 2 percent of sucrose, 0.9 percent of peptone, 0.1 percent of yeast powder, 0.25 percent of NaCl, CaCO 3 0.1%,MgSO 4 ·7H 2 0.1 percent of O and 0.0625 percent of defoaming agent. The fermentation broth is formulated in proportions with an initial pH of about 6.8. Sterilizing at 121 deg.C for 30min, cooling to 37 deg.C, inoculating seed liquid with age of 14h, with the inoculation amount of 2%. During the fermentation, the rotation speed is kept at 100rpm, the aeration ratio is 1:0.25vvm, and the tank pressure is 0.05 MPa. Culturing for 10h as fermentation end point, and detecting viable count of lactococcus lactis 3-c-18 of about 7.4 × 10 10 CFU/mL。
Adding sterilized high concentration saline water into the fermentation liquid to inhibit fermentation of lactobacillus, wherein the final concentration of NaCl in the fermentation liquid is 10%.
Example 4 application of lactococcus lactis (L.lactis)3-c-18 in mandarin fish farming
The experiment researches the influence of the addition of lactobacillus bacteria solutions with different concentrations on the mandarin fish. The experimental lactobacillus is lactococcus lactis 3-c-18 separated from the intestinal tract of the mandarin fish.
The experimental mandarin fish is siniperca chuatsi, and can be fed with artificial compound feed well after domestication. The experimental feed is special mixed powder for mandarin fish produced by agriculture and aquatic product science and technology group in northeast of Fujian province, and is prepared into soft granules by adding water for feeding.
Mandarin fish 640 tails with initial weight of 47.74 ± 5.70g were randomly divided into four groups, one control group and three experimental groups, with no significant difference in the initial weight of the four groups. Each treatment group had 4 replicates of 40 fish each, with an experimental period of 60 days.
The control group mandarin fish is fed with feed without lactobacillus, and the experimental groups 1, 2 and 3 are fed with feed containing lactococcus lactis 3-c-18 bacterial solution, and the effective bacteria number in the final feed is about 1 × 10 5 CFU/g、1×10 6 CFU/g、1×10 7 CFU/g。
After the experiment is finished, sampling is carried out after 24h of fasting, and relevant indexes are measured. Detecting the growth performance, serum and liver biochemical indexes of the mandarin fish, and performing challenge experiments on the residual mandarin fish after the experiments.
As can be seen from FIG. 2, the weight gain rate and feed coefficient of mandarin fish in experimental group 1 and experimental group 2 are significantly better than those in control group and experimental group 3(P < 0.05), which indicates that lactobacillus fermentation broth with appropriate concentration has a growth promoting effect.
From fig. 3, it can be seen that the serum glutamic-oxaloacetic transaminase (AST) activity and the Malondialdehyde (MDA) content of the mandarin fish in the experimental group are both significantly lower than (P < 0.05) that in the control group; and the lactococcus lactis 3-c-18 with a certain concentration is added into the feed, so that the alkaline phosphatase (ALP) and alanine Aminotransferase (ALT) activities of the blood serum of the mandarin fish and the content of Glucose (GLU) can be reduced, and the Catalase (CAT) activity is improved. The results show that the addition of a proper amount of lactococcus lactis 3-c-18 in the feed can improve the nutrient metabolism of the mandarin fish and improve the health level of the mandarin fish.
As can be seen from FIG. 4, the addition of lactococcus lactis 3-c-18 in the feed can significantly improve the activity of liver acid phosphatase (ACP), alkaline phosphatase (ALP) and Lysozyme (LZM), indicating that the health level of the liver of the mandarin fish is improved after the mandarin fish ingests the feed and is added with lactococcus lactis 3-c-18.
As can be seen from FIG. 5, the addition of lactococcus lactis 3-c-18 in the feed can significantly improve the resistance of the mandarin fish to aeromonas hydrophila.
The experimental results show that: the addition of a proper amount of siniperca chuatsi source lactococcus lactis 3-c-18 in mandarin fish culture can promote growth, improve nutrient metabolism of mandarin fish, improve health level of liver tissue, and enhance resistance to aeromonas hydrophila infection.
Example 5 application of lactococcus lactis (l.lactis) MG1614 derived from non-mandarin fish in mandarin fish farming
The experiment researches the influence of different concentrations of the non-mandarin fish source lactobacillus bacterial liquid added into the feed on the mandarin fish. Experimental Lactobacillus is lactococcus lactis MG1614 isolated from MG1614 lactococcus lactis powder. After activation in the laboratory, a bacterial solution with a certain concentration is prepared.
The control group mandarin fish is fed with feed without lactobacillus, and the experimental groups 1, 2 and 3 are fed with feed containing lactococcus lactis MG1614 bacterial liquid, and the final effective bacterial count in the feed is about 1.8 × 10 5 CFU/g、2.1×10 6 CFU/g、1.2×10 7 CFU/g。
The experimental mandarin fish, experimental design and cultivation management were the same as those in example 4.
From fig. 6, it can be seen that the fatness, the weight gain rate, the survival rate and the feed coefficient of the mandarin fish in the experimental group are not significantly different from those in the control group. This indicates that the fermentation liquid of non-mandarin fish source lactic acid bacteria MG1614 has no obvious effect on the growth of mandarin fish.
As can be seen from fig. 7, the addition of high concentration of lactococcus lactis MG1614 in the feed can significantly improve the resistance of mandarin fish against aeromonas hydrophila.
Example 6: application of lactococcus lactis (L.lactis) S6-2 derived from non-mandarin fish in mandarin fish culture.
The experiment researches the influence of different concentrations of non-mandarin fish source lactobacillus bacterial liquid added into feed on mandarin fish. The lactococcus lactis S6-2 for experiments is a strain preserved in a laboratory, and the preservation number is CGMCC No. 9135. After activation in the laboratory, a bacterial solution with a certain concentration is prepared.
The control group mandarin fish is fed with feed without lactobacillus, and the experimental groups 1, 2 and 3 are fed with feed added with lactococcus lactis S6-2 bacterial solution, and the final effective bacterial count in the feed is about 2.3 × 10 5 CFU/g、1.4×10 6 CFU/g、1.6×10 7 CFU/g。
The experimental mandarin fish, experimental design and cultivation management were the same as those in example 4.
From fig. 8, it can be seen that the fatness, survival rate and feed coefficient of the mandarin fish in the experimental group are not significantly different from those in the control group. The weight gain rates of the experimental groups 2 and 3 of mandarin fish are not obviously different from those of the control group, which shows that the fermentation liquor of the non-mandarin fish source lactobacillus S6-2 has no obvious effect on the mandarin fish growth.
As can be seen from FIG. 9, the addition of lactococcus lactis S6-2 to the feed had no significant effect on the resistance of mandarin fish against Aeromonas hydrophila infection.
Although the embodiments have been described, once the basic inventive concept is obtained, other variations and modifications can be made by those skilled in the art, so that the above embodiments are only examples of the present invention, and not intended to limit the scope of the present invention, and all the modifications of the equivalent structure or equivalent processes performed in the present specification, or directly or indirectly applied to other related fields are included in the scope of the present invention.