title: Study of changes in bacterial and viral abundance in formaldehyde-fixed water samples by epifluorescence microscopy.
abstract: Accurate measurement of bacterial and viral abundance in coastal marine environments is important to understand the dynamics of microbial communities in these ecosystems. In this study, the effect of formaldehyde preservation on the abundance of bacteria and viruses in water samples from Cochin Backwater was determined by SYBR Green I staining and epifluorescence microscopy. The counts were determined for 45 days in samples fixed with 1-6% formaldehyde. The results suggest rapid decline in counts of bacteria and viruses in samples preserved in formaldehyde, and the decline increased with increase in the final concentration of formaldehyde in the sample. The initial bacterial and viral counts in the sampling site were 5.2 × 10(6)/ml and 3.9 × 10(7)/ml, respectively. The bacterial count dropped by 5.1%, 53.3%, 55.7%, and 85% after 1, 7, 15, and 45 days, respectively, in sample fixed with 1% formaldehyde. The decline in viral counts was higher, being 32.4%, 47.9%, 68.1%, and 93% after 1, 7, 15, and 45 days, respectively. Storage of fixed samples at - 20°C did not halt the decline in microbial counts, suggesting that, irrespective of storage temperature, formaldehyde-fixed samples lead to underestimation of microbial counts.
authors.affiliation: Molecular Biology Laboratory, National Institute of Oceanography, Regional Center (CSIR), Dr. Salim Ali Road, P.B No. 1913, Kochi 682 018, India. parubfsc@yahoo.co.in
authors.forename: Ammini
authors.initials: A
authors.lastname: Parvathi
authors.forename: Seetha
authors.initials: S
authors.lastname: Radhakrishnan
authors.forename: M P
authors.initials: MP
authors.lastname: Sajila
authors.forename: Breezy
authors.initials: B
authors.lastname: Jacob
mesh_terms: D001419:Bacteria / Q000254:growth & development / Q000302:isolation & purification; D015169:Colony Count, Microbial / Q000379:methods*; D005404:Fixatives / Q000737:chemistry*; D005557:Formaldehyde / Q000737:chemistry*; D008856:Microscopy, Fluorescence; D012623:Seawater / Q000382:microbiology* / Q000821:virology*; D014780:Viruses / Q000254:growth & development / Q000302:isolation & purification; D014871:Water Microbiology; D014874:Water Pollutants, Chemical / Q000737:chemistry
chemical_list: D005404:Fixatives; D014874:Water Pollutants, Chemical; D005557:Formaldehyde