Marine microbiology

Microbial partners provide beneficial and detrimental functions to their hosts and other microbes through the exchange of metabolites and info chemicals. Developing an understanding of these micro-interactions has considerable implications for human health, agriculture, and ecosystem protection. Here, the microbial interactions of two important marine organisms: the Forcepia sp. sponge, a source of the potential anticancer compound, lasonolide A (LSA), and Pyrodinium bahamense, a dinoflagellate which produces the potent neurotoxin, saxitoxin, were investigated. Chapter 1 introduces marine microbial interactions, their importance in the function of organisms and ecosystems, and their applications in human health, agriculture and ecosystem production. Chapter 2 describes the identification and capture of the lasonolide biosynthetic pathway from a metagenomic fosmid library. This chapter also describes the assembly of the pathway into an expression vector and attempts to sustainably produce LSA through heterologous expression. Chapter 3 describes the identification and characterization of the bacterial associates of Pyrodinium bahamense, a toxin producing dinoflagellate found in the northern Indian River Lagoon. This chapter also describes potential chemical and molecular interactions occurring between P. bahamense and its associated cultivable bacteria. Chapter 4 describes the investigation into the effects microbial associates have on the physiology of P. bahamense. The completion of this work further describes microbial interactions occurring in marine environments, their influences and functions in the physiology and evolution of marine organisms, and the tools available for their investigation and utilization for human and ecosystem benefit.

Marine bacteria are usually described as those bacteria
which grow optimally in sea water. Their complex requirements
for specific ions (sodium, potassium and magnesium)
have been used to differentiate marine from terrigenous
bacteria. These requirements, however, vary at the gene level
through mutation. Both spontaneous and induced (ultraviolet
light) mutations to loss of the ion requirement were observed.
Spontaneous frequencies were low (below 10^-6); induced frequencies,
high (10^-1 to 10^-8). Back mutations were noticed.
A stepwise mechanism was postulated for the mechanism of the
mutation involved in the appearance of ion independent
bacteria in a population of cells. Genetic analysis of the mechanism by which variations
in ion requirements occurred included determination of base
ratios and of transformation frequencies. The base ratios
of mutant and parent bacteria were similar enough and the
transformation frequencies high enough (10^-3 to 10^-5) to
show a close relationship between the two types of bacteria. This similarity indicated that, although the genome of
marine bacteria, which clearly controls the requirement
for specific ions from the values of mutation frequencies,
is altered by the action of ultraviolet light, the change
was not observable by the methods used. The change could
have been induced on the gene level to effect the synthesis
of structural or functional proteins (enzymes).

Vibrio bacteria are emerging pathogens responsible for 80,000 illnesses and 100
deaths in the United States each year. Infections are directly linked to the marine
environment and are acquired by consuming contaminated seafood or exposing wounds
during aquatic activities. Florida has the highest national incidence of vibriosis, with 20%
of its cases reported from the Indian River Lagoon region, a popular recreation destination.
This study utilized a combination of cultivation and molecular techniques to investigate
the local distribution of V. vulnificus, V. parahaemolyticus and V. cholerae in this local
waterway. The targeted species were found in an array of samples which may facilitate their
transmission to humans. Overall, these bacteria were abundant in estuarine sediments (Vp:
2,439 CFU/g, Vv: 303 CFU/g, Vc: 176 CFU/g), on the sharp edges of oyster shells (Vp: 82
CFU/cm, Vv: 102 CFU/cm, Vc: 41 CFU/cm), and in the water column (Vp: 3.78 CFU/ml,
Vv: 5.51 CFU/ml, Vc: 2.46 CFU/ml). Vibrio also pose a hazard to recreational anglers as
they were recovered from fish (Vp: 61%, Vv: 55%, Vc: 30%), live bait shrimp (Vp: 80%,
Vv: 37%, Vc: 0%) and hooks (Vp: 32%, Vv: 18%, Vc: 0%). Additionally, a molecular
analysis of the V. vulnificus virulence revealed that the local population was dominated by
disease-causing (vcgC) strains, which may explain why wound-related infections are
common in this region.
Vibrio occurrence varied both spatially and temporally due to their relationship with
salinity and temperature. These bacteria exhibited a strong negative correlation with
salinity, being particularly abundant near freshwater discharge locations. Due to Florida’s
year-round warm climate, these species were found to be permanent members of the local
microbial community. Seasonal peaks in abundance occurred between August and
October, a period which corresponds with the warmest water temperatures as well as
frequent rainfall. Predictive models were constructed based on these parameters to provide
a better understanding of how, when and where Vibrio spp. may be encountered by humans.
This information is important for both water management and healthcare initiatives, with
an overall goal of improving local recreational safety.