Ecological Studies on Hydrocarbon-oxidizing Bacteria in Japanese Coastal Waters-III

Influence of Oil Pollution on Population Density of Hydrocarbon-oxidizing Bacteria

Abstract

It has been reported that the population density of some hydrocarbon-oxidizing bacteria was high in the oil-polluted area of the Seto Inland Sea caused by the Mizushima Oil Refinery Accident. On the other hand, little has been known as yet of the influences of environmental factors on the density of bacterial population.
The present paper dealt statistically with the data collected from the above-mentioned area in the four seasons for the purpose of clarifying the influences of several environmental factors on the density of hydrocarbon-oxidizing bacteria groups A and B (both groups are facultative hydrocarbon oxidizers, the former is counted in an organic nitrogen medium, the latter is counted in an inorganic nitrogen medium) as well as of heterotrophic bacteria in seawater and in bottom sediments. And then the group composition (heterotrophs, hydrocarbon oxidizer groups A and B) in the oil-polluted area and the control area was examined in the principal component analysis.
The results obtained can be summarized as follows:
1. In seawater, a significant correlation could be found between the oil content and the population density of hydrocarbon-oxidizing bacteria group A. The same was true of the density of both of group B and heterotrophic bacteria. lt is, therefore, presumed that the density of these groups of bacteria depends largely on oil pollutants.
2. The significance test of partial regression coefficients of a multiple linear regression equation in seawater of the oil-polluted area showed that the population density of heterotrophic bacteria (d_h) increased with √19-Cl (Cl: chlorinity in ‰) and with log d_p (d_p: oil content in ppm).
3. Though the population density of group A (d_a) was higher than that of group B (d_b) and showed a marked increase just after the oil spill accident, the results of variance analysis showed that closer was the correlation of d_b to d_p than that of d_a to d_p at all seasons.
4. In bottom sediments, the ratio of log d_b to log d_h in the polluted area was higher than that in the control area. Therefore, it can be said that this ratio may be one of the suitable indices for oil pollution.