PHYSIOLOGICAL ECOLOGY OF HETEROTROPHIC BACTERIA IN TWO INDIANA LAKES

CHARLES RICKEY LOVELL, Purdue University

Abstract

Rates of bacterial production of particulate organic carbon in two hardwater Indiana lakes were studied. Primary production rates were calculated from rates of photosynthetic H('14)CO(,3)('-) incorporation and bacterial (secondary) production from rates of ('3)H-(methyl)-thymidine incorporation by natural samples. Secondary bacterial production in Little Crooked Lake accounted for 31.8% of the April-October, 1982 and 29.4% of the April-September, 1983 total production (primary + secondary). Secondary production was 36% of the April-October, 1982 total in Crooked Lake. No photosynthetic sulfur bacteria were present in either lake. The vertical distribution of secondary production in both lakes and the seasonal distribution of secondary production in Little Crooked Lake were strongly influenced by primary production. The relationship of thymidine incorporation to rates of bacterial growth in diluted natural samples was used to calculate the conversion factor 2.2 x 10('18) cells produced (.) (mole thymidine incorporated)('-1). Calculated doubling times of Little Crooked Lake bacteria ranged from 0.35 - 12.00 days (median = 1.50 days) during the April-October, 1983 period. The percentage of bacterial production attached to particles retained on (GREATERTHEQ) 1.0 (mu)m pore size filters accounted for 2-19% of the total in the Little Crooked Lake water column from April-August of 1982 and 1983. The fraction of bacterial production attached to particles (GREATERTHEQ) 1 (mu)m diameter increased in late summer and fall when the cyanobacterial population underwent senescence. It appears that the supply of colonizable particles (damaged filaments) was an important factor affecting the degree of attachment of the bacterial population in Little Crooked Lake. Bacteria in Little Crooked Lake were found to be growing at suboptimal temperatures throughout most of the water column, even during the summer months. Even rapidly growing metalimnetic populations displayed no noticable adaptation to low environmental temperatures. This indicates that temperature could have limited the growth of bacteria in this lake throughout the period of thermal stratification. The extracellular release of photosynthetically fixed organic carbon by healthy phytoplankton was not found to be an important carbon source for planktonic bacteria. Slow carbon release mechanisms, such as algal decomposition, seem to have been more important.

Degree

Ph.D.

Subject Area

Microbiology

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