The Effects of Starvation on The Ruminal Bacteria Megasphaera Elsdenii and Selenomonas Ruminantium
Mink, Ronald William
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Permalink
https://hdl.handle.net/2142/68561
Description
Title
The Effects of Starvation on The Ruminal Bacteria Megasphaera Elsdenii and Selenomonas Ruminantium
Author(s)
Mink, Ronald William
Issue Date
1981
Department of Study
Dairy Science
Discipline
Dairy Science
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Microbiology
Language
eng
Abstract
The ruminal bacteria, Megasphaera elsdenii and Selenomonas ruminantium, were subjected to total organic nutrient starvation after growth in batch and/or continuous culture. Both organisms exhibited a very limited survival capacity in comparison to other bacteria reported in the literature. This capacity appears to have been at least partially influenced by pre-starvation growth conditions and levels of cell constituents. Because these conditions were constantly changing during batch culture growth, continuous culture growth was found to be more suitable as a basis for starvation studies. Depending on pre-starvation growth conditions, both M. elsdenii and S. ruminantium appeared to break down carbohydrate, RNA and/or DNA preferentially during starvation, suggesting that a degradation of carbohydrate storage material, excess ribosomes and/or extra genomes may have taken place. The role of protein degradation in survival of these organisms, if any, is unclear. Cellular RNA levels always exhibited relatively rapid decreases and were accompanied by either catabolism or excretion from the cell of the RNA or its components, depending on the organism and pre-starvation growth conditions. Those populations that did appear to catabolize these substrates tended to have a better survival capacity. However, no positive correlation could be found between survival ability and level of any single constituent.
M. elsdenii cultures grown at the dilution rate (D) of 0.13 h('-1) appeared to exhibit poorer long term survival than those grown at D = 0.24 h('-1). S. ruminantium grown under glucose-limitation at D = 0.25 h('-1) demonstrated a survival rate during the first 12 to 18 h of starvation poorer than populations grown at higher or lower dilution rates. After 18 h, survival appeared to be inversely related to dilution rate. In addition, these populations exhibited a bi- or multi-phasic pattern of variability decline which was attributed to refeeding of subpopulations on the products of previously lysed cells. The nature of these products is not known, but was apparently not vitamins. Selenomonas grown under ammonia-limitation exhibited survival ability which also appeared to be inversely related to dilution rate. The loss in viability of the population grown under ammonia limitation did not appear to be due to an inability to maintain suitable levels of essential catabolic or biosynthetic enzymes.
In most cases, cells that underwent starvation exhibited a shift in the pattern of fermentation acids produced, from a mixed acid production to exclusively or primarily acetogenesis, probably because of greater efficiency of energy production associated with such metabolism.
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