Molecular Identification and Characterisation of Extremophilic and Pathogenic Microorganisms from Water Samples Collected in the UK and Saudi Arabia

Water samples were collected from the rivers Lathkill and Bradford, Derbyshire UK and from the Al-Asfar lake and irrigation channels, Hassa, Saudi Arabia. The Derbyshire samples were incubated in rich growth medium at pH 10 and two alkaliphilic/alkalitolerant strains were isolated. Molecular identification techniques based on 16S rRNA gene sequencing suggested that both strains belonged to the Exiguobacterium genus of Gram-positive bacteria. The Hassa samples were incubated in highly saline rich growth media (up to 4 M NaCl) and three halophilic or halotolerant strains were isolated. In this case 16S rRNA gene sequencing identified the strains as Halomonas venusta, Halobacillus blutaparonensis and Staphylococcus warneri.
The Exiguobacterium strains were further characterised with respect to antibiotic sensitivity and carbon source utilisation. The compatible solute betaine was detected in Exiguobacterium cells grown at pH 10; this is the first report of a compatible solute being found in Exiguobacterium cells.
Halobacillus blutaparonensis and Staphylococcus warneri were further characterised and H. blutaparonensis was shown to accumulate betaine which allows growth at high salinity. However, H. blutaparonensis was unable to synthesise the alternative compatible solute ectoine and was therefore incapable of growth at high salinity in minimal medium. S. warneri is an important hospital acquired pathogen and it was interesting that it was found in the Hassa water. It also accumulated betaine to allow growth at high salinities.
Two strains (Exiguobacterium and S. warneri) were chosen for experiments examining the effect of UVC light (254 nm) on cell viability, DNA structure and cell morphology. On solid medium, both strains were susceptible to UVC light with most cells killed after a few minutes exposure. In liquid cultures, Exiguobacterium strain was more resistant. Gel electrophoresis studies showed that the DNA was degraded by increasing exposure to UV light, but no clear effects were seen on cell morphology using electron microscopy.