A tentative direct microscopic method for counting living marine bacteria.

Area of Science:

• Marine microbiology
• Bacteriology
• Microbial ecology

Background:

• Accurate enumeration of viable bacteria is crucial for understanding marine ecosystems.
• Traditional culture-based methods, like plate counts, often underestimate bacterial populations due to unculturable species.
• Direct microscopic methods offer potential for more comprehensive cell counts.

Purpose of the Study:

• To develop and validate a novel method for the direct count of viable bacterial cells (DVC) in marine environments.
• To compare the DVC method with traditional viable plate counts and total direct counts.
• To assess the efficacy of DVC for enumerating bacteria in open ocean samples.

Main Methods:

• Seawater samples were treated with yeast extract (0.025%) and nalidixic acid (0.002%).
• Incubation was performed for 6 hours at 20°C in the dark to induce filamentation without cell division.
• Elongated cells were quantified using direct microscopy and epifluorescence microscopy.

Main Results:

• The treatment resulted in elongated bacterial cells, distinguishable via microscopy.
• The direct count of viable bacterial cells (DVC) method yielded counts significantly higher than viable plate counts (up to three orders of magnitude).
• DVC counts were slightly lower than total direct counts (approximately one order of magnitude).

Conclusions:

• The proposed DVC method provides a more accurate assessment of viable marine bacteria compared to traditional plate counts.
• This technique enhances the understanding of microbial biomass and activity in oceanic waters.
• DVC offers a valuable tool for marine microbial ecology research and environmental monitoring.