Foot pustule disease is an important disease affecting abalones. In the present study, microbiological and histopathological investigations were carried out in the Japanese abalone Haliotis discus hannai, affected by foot pustule disease. Diseased abalones became lethargic, weak and eventually died. The remarkable symptoms were apparent foot pustules and atrophy of the foot muscle. A predominant bacterium designated as BV2 was isolated from the pustules of diseased abalones. Experimental infection by immersion challenge showed that BV2 was virulent to abalones and caused symptoms of foot pustule disease with median lethal dose value of ≈7.76×10 5 cfu ml -1 . BV2 was infectious to all tested abalones with high mortality. Histopathological investigations showed degeneration and collapse of foot muscles as well as connective tissues. Tissues in round pustules were necrotic and disorganised. The BV2 bacterium was identified as Vibrio harveyi based on the results of phenotypic and biochemical tests as well as 16S rRNA gene sequence analysis.. The bacterium was found resistant to kanamycin and clindamycin, and sensitive to other 11 antibiotics tested.

Macin is a family of antimicrobial peptides (AMPs) and is involved in the immune responses of marine mollusks. In the present study, a novel Mytimacin (denoted as Hd-mtmc 6) was identified from the small abalone Haliotis diversicolor by RNA-seq and RACE techniques. Hd-mtmc 6 contained a coding sequence of 243 bp and encoded 80 amino acids, with a putative peptide mytimacin 6 consisting of 61 amino acid residues. The mature peptide of Hdmtmc 6 exhibited typical characteristics of AMPs, including net positive charge (+4), higher hydrophobic residue ratio (37%), and lower molecular mass. Eight cysteines in the mature peptide formed four disulfide bond bridges (C1-C6, C2-C5, C3-C7, and C4-C8). Moreover, the presence of the macin domain, a threedimensional structure similar to that of hydramacin-1, and a phylogenetic relationship suggested that Hd-mtmc 6 could be a new member of the invertebrate macin family. In unchallenged abalone, the Hd-mtmc 6 transcript was expressed in all tested tissues and could be detected at different stages of embryonic development. Vibrio harveyi challenge caused a significant Hd-mtmc 6 transcripts upregulation within 2 -6 h in the mantle and hepatopancreas. Our results suggested that Hd-mtmc 6 may be involved in innate immune responses of small abalone. Further investigations are required to confirm its antibacterial activity at the protein level.

Milk clotting enzyme is an important enzyme in cheese industry, to obtain an industrial strain with high milk-clotting enzyme activity, Mucor miehei was used as the origin strain and mutagenized by Ultraviolet (UV) and UV combining lithium chloride(LiCl), respectively. The result shows that lower concentrations of LiCl can increase the survival rate of the spores treated with UV, while higher concentration of LiCl can increase the mortality of the spores treated with UV. The highest positive rate (reached 32.17%) was achieved in the compound mutation, which was higher than that of the UV mutagenesis (21.45%). On the basis of multiple mutation, a mutant UV-LiCl-6 was screened. The milk-clotting activity of UV-LiCl-6 reached 2703.58 SU/mL and was 57.70% higher than that of the parent strain. Results of the pass-generation test indicated that the strain had good genetic stability and may be ideal strains for the production of milk-clotting enzyme. Additionally, it was demonstrated that compound mutagenesis with UV and LiCl is an effective mutation method for the breeding of enzyme-producing strains.