Date of Award

Fall 1996

Project Type

Dissertation

Program or Major

Microbiology

Degree Name

Doctor of Philosophy

First Advisor

Richard Blakemore

Abstract

The seasonal abundance and distribution of mesophilic aeromonads at seven sites in Great Bay Estuary, NH were monitored over a 24 month period. Total heterotrophic bacteria, total and fecal coliforms, salinity, temperature, pH, total suspended solids, and chlorophyll were also measured in the samples. Aeromonads were isolated at each site throughout the year with the highest incidence and population density in the late summer to early fall. Aeromonad abundance correlated positively with the incidence of coliforms, temperature, and salinity.

Aeromonas hydrophila ATCC 7966 grew anaerobically by using NO$\sb3\sp-$, fumarate, Fe (III), Co (III), or Se (VI) as terminal electron acceptors. Of thirty isolates from Great Bay, 100% were capable of reducing NO$\sb3\sp-$, Fe (III), and Co (III), and 43% carried out dissimilatory Se (VI) reduction. Final cell yields of A. hydrophila ATCC 7966 increased in direct proportion to the amount of oxidant provided (over the range 1.25-10 mM). Cells of A. hydrophila ATCC 7966 contained c-type cytochromes (420, 522, 553 nm). Hydrogen-reduced cytochromes were oxidized by Fe (III) or NO$\sb3\sp-$. Extracts of cells grown anaerobically with Fe (III), reduced it at a rate of 116 nmol$\cdot$min$\sp{-1}\cdot$mg protein$\sp{-1}$. Electron transport was inhibited by $\mu$m concentrations of: HOQNO (76%), quinacrine (88%), dicumarol (58%) oxygen (96%), CCCP (83%) and sodium azide (36%) and to a lesser extent by rotenone (18%). The results were consistent with the involvement of FAD dehydrogenase, quinones, cytochromes and an iron reductase in the respiratory chain.

Co-culturing Aeromonas veronii and a dissimilatory iron-reducer Shewanella alga resulted in enhanced growth, citrate degradation and iron reduction as compared to the extent observed with either strain grown axenically. By 48 hours, the co-culture consumed twice as much citrate and produced half as much formate and twice as much acetate. The synergistic link between these two organisms was apparently formate: produced by A. veronii, it was, in turn, used as a substrate for iron reduction by S. alga.

Download

Share

COinS