Trichoderma species were known as biological control agents against phytopathogenic fungi because they produce a variety of chitinases. Chitinases are hydrolytic enzymes that break down glycosidic bonds in chitin, a major component of the cell walls of fungi. The present study shows that extracellular chitinase activity reached a maximum value of approximately 22 U/mL after 96 h of T. asperellum PQ34 strain culture. The optimal temperature and pH of enzyme are 40°C and 7, respectively, whereas the thermal and pH stability range from 25°C to 50°C and 4 to 10, respectively. Chitinase at 60 U/mL inhibited nearly completely in vitro growth of Colletotrichum sp. (about 95%) and Sclerotium rolfsii (about 97%). In peanut plants, 20 U/mL of chitinase significantly reduced the incidence of S. rolfsii infection compared to controls. The fungal infection incidence of seeds before germination and 30 days after germination was only 2.22% and 2.38%, while the control was 13.33% and 17.95%. Besides, chitinase from T. asperellum PQ34 can also prevent anthracnose that is caused by Colletotrichum sp. on both mango and chilli fruits up to 72 h after enzyme pretreatment at 40 U/mL. In mango and chilli fruits infected with anthracnose, 40 U/mL dose of chitinase inhibited the growth of fungi after 96 h of treatment, the diameter of lesion was only 0.88 cm for mango and 1.45 cm for chilli, while the control was 1.67 cm and 2.85 cm, respectively.

Four Trichoderma strains (CH2, SH16, PQ34, and TN42) were isolated from soil samples collected from Quang Tri and Thua Thien Hue provinces in Vietnam. The strains exhibited high chitinolytic secretion. Strain PQ34 formed the largest zone of chitinase-mediated clearance (> 4 cm in diameter) in agar containing 1% (w/v) colloidal chitin. Analysis of the internal transcribed spacer regions of these strains indicated that they were Trichoderma asperellum. The molecular weights of the chitinases were approximately 42 kDa. Chitinase genes (chi42) of T. asperellum strains TN42, CH2, SH16, and PQ34 were 98~99% homologous to the ech42 gene of T. harzianum CB-Pin-01 (accession No. DQ166036). The deduced amino acid sequences of both T. asperellum strains SH16 and TN42 shared 100% similarity.

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We cloned two genes coding F107-C and K88-1NT fimbrial subunits from strains E. coli C and 1NT isolated from Thua Thien Hue province, Vietnam. The mature peptide of faeG gene from strain E. coli 1NT (called faeG-1NT) is 100 % similarity with faeG gene, while the CDS of fedA gene from strain C (called fedA-C) has a similarity of 97 % with the fedA gene. Expression of the faeG-1NT and fedA-C genes in E. coli BL21 Star TM (DE3) produced proteins of *31 and 22 kDa, respectively. The effect of IPTG concentration on the K88-1NT and F107-C fimbriae production was investigated. The results showed that 0.5 mM IPTG is suitable for higher expression of K88-1NT subunit, while 0.75 mM IPTG strongly stimulated expression of F107-C subunit. The optimal induction time for expression was also examined. Generally, highest expression of K88-1NT subunit occurred after 6 h of induction, while that of F107-C subunit is after 14 h.

Objective: This study was done to report the results of genetic diversity and toxic genes analysis of Vibrio pathogen isolated from white leg shrimp and marine fishes cultured in Thua Thien Hue province, Vietnam. Methods/statistical analysis: Pathogen Vibrio spp. were isolated from shrimps and fishes, and were identified by 16S rRNA sequencing. The presence of toxin genes in Vibrio spp. strains were determined through the presence of genes encoding toxic proteins (pirAvp, pir-Bvp, tlh, tdh and trh) based on specific primers for these genes. Genetic diversity of Vibrio strains was analysed by RAPD technique. Findings: A total of 120 Vibrio colonies from shrimps (with Acute Hepatopancreatic Necrosis Disease) and fishes (with hemorrhagic disease) cultured in Tam Giang lagoon in Thua Thien Hue, Vietnam were isolated. Of which, 14/54 strains from shrimps had pirAvp and pirBvp genes and 18/66 strains from fishes had tlh gene, and none of Vibrio strains had tdh and trh genes. Randomly amplified polymorphic DNA (RAPD) analysis of 36 Vibrio samples showed the 148 polymorphic DNA fragments from ten random primers. The genetic diversity is high within studied species. In there, V. parahaemolyticus has the highest diversity level (h=0.1645 and I=0.2695) while V. shilonii is lowest (h=0.0136) and I=0.0207). The degree of genetic differentiation among species is also high (Gst=0.4827). Genetic identity between V. parahaemolyticus and V. vulnificus (0.9545) is highest while between V. shilonii and V. harveyi (0.7416) is lowest. The dendrogram also showed that V. parahaemolyticus is closely related to V. vulnificus whereas V. shilonii and V. harveyi have large distance. Application/improvements: This study is aimed to provide scientific data as the basis for the study and production of rapid diagnostic kits in the future.