Isolation and characterization of environmental vibrio species from Mai Po Nature Reserve, Hong Kong
ISOLATION AND CHARACTERIZATION OF ENVIRONMENTAL VIBRIO SPECIES FROM MAl PO NATURE RESERVE, HONG KONG
Submitted by Wang Yanling
for the degree of Master of Philosophy at The University of Hong Kong
in December 2003
Mai Po Nature Reserve, the largest wetland in Hong Kong, contains a variety of unique habitats. It is intensively used by a diverse population of migratory birds as the feeding ground and "refueling site" in winter. Due to its vicinity next to the Shenzhen River and Sham Pui River, Mai Po Nature Reserve is confronted with pollution threats by domestic sewage and industrial wastewater discharges. The brackish water containing high concentrations of organic nutrients may nourish heterotrophic bacteria including Vibrio species, some of which may pose potential hazards to the public, marine lives and migratory birds.
In this study, a total of 32 environmental strains of Vibrio species were isolated in sediment and water samples obtained from Mai Po. Three of them, displaying high similarity to reference strains in API 20 NE biochemical testing, were identified as Vibrio cholerae MP-l, Vibrio estuarianus MP-2 and Vibrio vulnificus MP-3 with 16S rDNA sequencing. All three isolates showed distinctive responses to environmental
parameters. Low temperature at 15?, inhibiting V. cholerae MP-l completely, slowed
the growth of V. estuarianus MP-2 and V. vulnificus MP-3. Adapted to a wide range of pH, V. cholerae MP-l grew almost equally well between pH 5.2 and 9.2. Both V. estuarianus MP-2 and V. vulnificus MP-3 required Na+ during their growth, but high salinity at 6 % was inhibitory to the growth of all three isolates.
V. cholerae MP-l was surprisingly tolerant to a high concentration of vibrio static agent 0/129 at 40 gYml, while the growth of V. estuarianus MP-2 and V. vulnificus MP-3 was completely stopped. All three isolates were strongly resistant to ampicillin, bacitricin, penicillin G and erythromycin but were very susceptible to tetracycline, chloramphenicol, nalidix acid, streptomycin and nitrofurantoin. Sulphatriad,
sulphamethizole and sulphamethoxazole did not effectively inhibit V. cholerae MP-I and V. vulnificus MP-3, but effectively inhibited V. estuarianus MP-2. V. cholerae MP-I was also found to be resistant to a high concentration of ethidium bromide at 500 glm1.
A naturally occurring plasmid was observed and then isolated from V. cholerae MPI while no plasmid was detected in the other two isolates. This plasmid, designated as pVC, was 3,806 base pairs in length. Its full sequence was determined and deposited in GenBank under the accession number AY 423429. Five Open Reading Frames (ORPs) were tentatively deduced, but no observable phenotypic characteristic has been identified for this small cryptic plasmid so far. The unsuccessful attempts to cure pVC from V. cholerae MP-I suggest its close relationship with the host strain over the long evolutionary history. Overall, this study suggests that Mai Po Nature Reserve harbors some unique bacterial species with unknown biological characteristics, and that further investigation of the microbial and plasmid ecology is warranted.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:vibrio china hong kong bacterial genetics mai po
Date of Publication:01/01/2004