14 Dec 2018
Sinorhizobium meliloti Bacteriophage HMSP-1-Susan: Genome Sequence, Molecular Characterization and Implications for Symbiosis
Brennon Fleagle '18
Bacteria of the genus Sinorhizobium are plant-growth promoting microbes that form symbiotic relationships with legumes. These bacteria are important in agriculture because of their ability to convert atmospheric nitrogen gas to ammonia. Ammonia is used to synthesize proteins essential for plant growth. Bacteriophages are bacterial viruses that decrease microbial populations in soils and other environments. Despite extensive research on the molecular mechanisms governing the process of nitrogen fixation in Sinorhizobium, little is known about the biotic factors that influence the persistence of these bacteria in soil and impact their ability to fix nitrogen. The presence of bacteriophages in soils has been shown to select for specific types of Sinorhizobium strains and to affect the populations nitrogen-fixing bacteria. In spite of this observation, there are only a limited number of Sinorhizobium phages that have been characterized. The goal of this project was to carry out a molecular characterization of phage HMSP-1, a bacteriophage isolated from an agricultural soil that infects strains of Sinorhizobium. Viral DNA was isolated and used to obtain the complete nucleotide sequence of HMSP-1. Genome analyses revealed that HMSP-1 is a double stranded DNA virus of 52 kb in size. The genome has a GC content of 52.5% and encodes 96 proteins. 83 percent of these proteins were classified as hypothetical proteins of unknown function. HMSP-1 did not have significant DNA sequence homology to known bacteriophages; these data suggest HMSP-1 is novel bacterial virus. We investigated the effects of bacteriophage HMSP-1 on plant growth and the numbers of Sinorhizobium associated with the model legume, Medicago truncatula. No significant differences in growth or microbial numbers were found between the plants exposed to the phage and unexposed the controls. These data suggest that under the conditions tested, HMSP-1 does not affect the bacterial populations associated with Medicago truncatula.
Antibiotic-Resistant Bacteria in Minnesota Lake Sediment of Varying Productivity
Jaimen Hampton '18
Management of bacterial diseases has been present in clinical settings since the 1940s when antibiotics became prevalent. (Sengupta, 2013) Yet, antibiotics have long been utilized by bacteria before clinical use meaning that antibiotics and antibiotic-resistant genes (ARG) occur naturally within the environment. Anthropogenic factors such as the use of antibiotics in agriculture and misuse of antibiotics in treatment can expedite dissemination of ARG’s that occur in the environment. This results in bacteria that can become super-resistant and host a variety of ARG’s. Environmental factors such as the trophic level of a lake can have an effect on the density of microbial communities. Oligotrophic lakes, which are generally low in nutrients (nitrogen and phosphorus), support a smaller biomass of bacteria than mesotrophic lakes and eutrophic lakes. Having a larger bacterial community allows for an increase of antibiotic-resistant bacteria (ARB) and ARG’s. ARB that are well adapted to their respective environment can transduce their ARG’s to a neighboring bacterium, this allows for other genus or species of bacteria to become better adapted to their environment which adds to the increasing community of ARB’s within a lake. The focus of this research was to analyze lake sediment samples and identify ARB within each lake.