Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
A method for measuring microbial degradation and mineralization of radiolabeled native chitin is described. ('14)C-labeled chitin was synthesized in vivo by injecting shed blue crabs (Callinectes sapidus) with N-acetyl-D- ('14)C -glucosamine, allowing for its incorporation into the exoskeleton. The cuticle had a total organic content of 0.48 mg C mg('-1) with a specific radioactivity of 6762 DPM mg('-1). Glucosamine i.e. chitin content, as determined colorimetrically, was 22% (w/w). Rates of chitin degradation and mineralization in estuarine water and sediments were determined as functions of temperature, inoculum source, and oxygen condition. Significant differences in rates between temperature treatments were evident. Q(,10) values ranged from 1.2 to 2.5 for water and sediment, respectively. Increased incubation temperature also resulted in decreased lag times before onset of chitinoclastic bacterial growth and chitin degradation. The highest rate, 284 mg day('-1)g('-1) seeded chitin, occurred in the water column inoculum at 25ï¿½C. The lowest rate, 83 mg day('-1) g('-1), was found in the anaerobic mud inoculum incubated at 15ï¿½C. Over 95% of particulate chitin degraded by water column bacteria was mineralized to CO(,2) with no apparent lag between processes. No measurable dissolved pool of radiolabel was present. Conversely, only 75-80% of chitin degraded by sediment inocula was mineralized. Label recoveries in the dissolved pool ranged from 6 to 17%. The anaerobic treatment possessed the highest pool of dissolved organic carbon due to the fermentation of chitin to volatile fatty acids. The anaerobic pathway of chitin decomposition by chitinoclastic bacteria was examined with an emphasis on end product coupling to other bacterial types. Actively growing chitinoclastic bacterial isolates produced primarily acetate, hydrogen, and carbon dioxide in broth culture. No sulfate reducing or methanogenic isolates grew on chitin as sole carbon source nor produced any measureable degradation products. Mixed cultures of chitin degraders and sulfate reducers resulted in positive sulfide production. Mixed cultures of chitin degrading isolates with methanogens resulted in the production of methane with concurrent reductions in headspace hydrogen and carbon dioxide. The combination of all three metabolic types resulted in the simultaneous production of methane and sulfide. More methane was produced in mixed cultures containing CO(,2)-reducing methanogens and acetoclastic sulfate reducers due to less interspecific hydrogen competition.
© The Author
Boyer, Joseph N., "Degradation and mineralization of chitin in an estuary" (1987). Dissertations, Theses, and Masters Projects. Paper 1539616579.