BackgroundThere are still a large variety of microorganisms among aquatic animals, especially probiotic lactic acid bacteria in cold water fishes at high latitudes have not been fully developed. Hence, the present study aims to evaluate the probiotic potential of cold-adapted Lactobacillus strains isolated from the intestinal tract of cold water fishes (Xinjiang) and select candidates to be used as new food preservative agents and/or probiotic additives in feeding of aquaculture.ResultsA total of 43 Lactobacillus spp. were isolated from 16 kinds of intestinal tract of cold-water fishes. They were characterized by phenotypic methods, identified using Rep-PCR and 16S rRNA gene sequencing as four species: Lactobacillus sakei (22 isolates), Lactobacillus plantarum (16 isolates), Lactobacillus casei (4 isolates) and Lactobacillus paracasei (1 isolate). The in vitro tests included survival in low pH and bile, antimicrobial activity (against Escherichia coli, Salmonella enterica subsp. enterica serovar Typhimurium, Salmonella enterica subsp. enterica, Listeria monocytogenes, and Listeria innocua), resistance to 15 antibiotics and hemolytic tests. Among all 43 lactobacilli isolates, the 22 isolates showed a wide range of antimicrobial activity against 6 different pathogenic strains. There were twenty isolates growing at optimal temperature ranging 16~20 °C, which were initially considered to be cold-adapted strains. Two (2) Lb. sakei strains and 2 Lb. plantarum strains demonstrated the highest survivability after 4 h of exposure at pH 2.0. Most of the tested strains cannot be cultured after exposed into 0.5% bile solution for 4 h, while 2 Lb. plantarum strains (E-HLM-3, CQ-CGC-2) and 1 Lb. sakei strain M-DGM-2 survived even at 2% bile concentration. In addition, the safety assessment showed that 22 strains without any detectable hemolytic activity and resistant to glycopeptides (vancomycin, teicoplanin), levofloxacin, aztreonam, amikacin and oxacillin, while all the studied lactobacilli showed sensitivity to or semi-tolerant to other antibiotics.ConclusionsBased on all the experiments, 3 strains, including E-HLM-3, CQ-CGC-2, and M-DGM-2 might be a candidate of choice for using in the food preservative agents and/or probiotic additives in feeding of aquaculture.

Negative refractive index (NRI) of the quantized lossless mesoscopic left-handed transmission line (LHTL) is deduced numerically in thermal Fock state. Some specific quantum features of NRI dependent the temperature, frequency of the electromagnetic wave and photon numbers, and quantum fluctuations are shown in the lossless LHTL. The results are significant for the miniaturizing applications of LHTL and quantum circuits. Keywords Negative refractive index · Mesoscopic Left-handed transmission lines · Thermal Fock state 1 Introduction The theoretical speculation of negative refractive index materials (NRM) proposed by V. Veselago[1] in 1968, in which several fundamental phenomena occurring in or in association with NRM were predicted, such as the negative Goos-Hänchen shift[2], amplification of evanescent waves[3], reversals of both Doppler shift and Cerenkov radiation[1], sub-wavelength focusing[4] and so on. Some typical approaches for NRM can be summarized as artificial structures such as metamaterials[5-7] and photonic crystals[8-10], chiral materials[11] and photonic resonant media[12, 13]. Although very exciting from a physics point of view, the artificial structures seem to be of little practical interest for engineering applications because

Starting from the quantum fluctuation of current in the mesoscopic composite rightleft handed transmission line (CRLH-TL) in the thermal Fock state, we investigate the left-handedness dependent of the frequencies, intensity and quantum fluctuations of the current field in the CRLH-TL under different thermal environment. The results show that the intensity and quantum fluctuations of current field in lower frequency bands affect the left-handedness distinctly under different thermal environment. The thermal effect on the left-handedness in the mesoscopic CRLH-TL deserves further experimental investigation in its miniaturization application.

The left-handedness was demonstrated in an E 3+ r -dopped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAFN) optical fiber modeled by a three-level quantum system. Under the electric and magnetic components of the probe field driving the transitions of 4 I 15/2 -4 I 13/2 and 4 I 9/2 − 4 I 13/2 in the E 3+ r -dopped optical fiber respectively, an increasing left-handedness was achieved by the incremental incoherent pumping field. However, the left-handedness damped when the incoherent pumping field drove the transition heavily. Our scheme may provide a solid candidate other than the coherent atomic vapour for left-handedness, and may extend the application of the rare-earth-ion-doped optical fiber in metamaterials via the external incoherent pumping field.

Negative refractive index (NRI) of the mesoscopic dissipative left-handed transmission line (LHTL) is manipulated by the displaced squeezed Fock state and the dissipation presented by the resistance and conductance. Compared with the classical LHTL, some novel characteristics of NRI are shown in the LHTL because of the quantum effect, which will be significant for its miniaturization application in microwave frequency.