The Feeding Ecology Of Two Protozoa And The Interaction With The Crude Oil Degrading Bacteria

Free-living protozoans, with high species richness and diverse feeding strategies, are important members of microbial food webs and playing an important role in aquatic ecosystems. Strengthen and expend the researches on protozoan feeding ecology will contribute to understanding on the structure, function and the process of water ecosystems. The effects of initial food concentration and culture temperature on the population growth of heterotrophic flagellate Bodo saltans and ciliate Tetrahymena priformis, the effects of bacteria metabolic activity on the feeding rate of T. priformis, the degradation ability of T. priformis culture, and the impact of T. priformis grazing on the crude oil biodegradation of Acinetobacter baumannii were studied under laboratory conditions. The results are as follows:（1） When the initial food concentrations were 2.10×10⁶, 2.80×10⁶, 4.20×10⁶ and 6.40×10⁶ cell/mL, the population growth rates were 0.1166, 0.1376, 0.1202 and 0.1128 h^-1, and the generation time were 5.90, 5.00, 5.80 and 6.10 h, respectively. Culture temperature also had significant effect on the population growth of B. saltans. When the culture temperature were 10℃, 20℃and 30℃, the population growth rates of B. saltans were 0.0500, 0.1246, and 0.1203 h^-1, and the generation time were 13.86, 5.60, and 5.80 h, respectively. When culture temperature increased from 10℃to 20℃, B. saltans had a 2.49 times increase in population growth rate, the corresponding generation time reduced 8.3 h; and when the culture temperature increased from 20℃to 30℃, there were no significant changes in the maximum population growth rate and generation time. Compared with other heterotrophic flagellates （eg. Choanoflagellates） with similar size, Bodo was characterized by rapider population growth and shorter generation time.（2） When the initial food concentrations were 7.50×10⁶, 1.50×10⁷, 3.00×10⁷and 6.00×10⁷ cell/mL, the population growth rates were 0.0700、0.0870、0.0920 and 0.0830 h^-1, and the generation time were14.30, 11.40, 10.90 and 12.00 h, respectively. Culture temperature also had significant effect on the population growth of T. priformis. When the culture temperature were 10℃, 20℃and 30℃, the population growth rates of T. priformis were 0.0400, 0.0800 and 0.0700 h^-1, and the generation time were 19.80, 8.55 and 9.59 h, respectively. Compared with B. saltans, T. priformis exhibit the same response trend.（3） T. priformis grazing rate on live bacteria was 7.43±0.09×10⁴ bac.ciliate^-1h^-1, while grazing rate on heat-killed bacteria was 5.96±0.23×10⁴ bac.ciliate-1h-1, grazing rate on live bacteria was 1.25 times greater than grazing rate on heat-killed bacteria, indicated that T. priformis prefer feeding on the metabolically active bacteria.（4） When the initial crude oil concentrations were 0.25%, 0.5%, and 1%, the crude oil degradation rates by culturing T. priformis in wheat grains culture were 68.08%, 60.92% and 37.40% respectively. The results indicated that culturing T. priformis in wheat grains culture had a strong ability to degradate crude oil.（5） When the population of T. priformis was added into the A. baumannii degrading system, due to the effects of T. priformis grazing, the population size of degrading bacteria significantly decreased （P<0.01）, while the degrading efficiency of each bacteria was increased by 5.43 times （1%）, 9.05 times （0.5%）, 10.40 times （0.25%） respectively. The analysis of variance showed that: T. priformis grazing could significantly increase the degrading efficiency of the bacteria （P<0.01）.