I am extremely grateful and express my deep sense of gratitude to my advisor, Dr Julia Maresca, for her guidance, constant supervision, keen interest, support and steady encouragement throughout the course of preparation and completion of my academic project and thesis. Her constant encouragement and advice has helped me transform into a better student, writer and research assistant.
I would like to thank all the present and past Maresca lab members- Dr Jessica Keffer for her patience while training me ; Erik Kiledal, Priscilla Hempel, Christie Chapman, Emma Smith for their patience and valuable suggestions which has helped me improve my presentation skills. Additionally, I would like to thank my committee members- Dr Carlton Cooper and Dr Karl Schmitz for their guidance and scientific expertise.
I would also like to thank my roommates for always lending an ear and being a great support system. At last but not the least, my words run few to express my gratitude to my parents and my grandmother, whose guidance, blessings and support is the reason I stand here.
Sunlight is a source of energy for phototrophic organisms and the ecosystems they are a part of. The concept of light utilization in primary producers is well understood in the scientific community. How sunlight acts as a signal and regulates processes in heterotrophs is a concept that is not well characterized in most species. Two heterotrophic actinobacterial strains lacking functional photosystems exhibit enhanced growth in the light. The aim of this study is to characterize the physiological effects light has on these strains. We discovered that the strains of actinobacteria- namely Rhl. lacicola and Aurantimicrobiumsp strain MWH-Mo1, grow significantly better in the light than in the dark due to upregulation of sugar transport and metabolism genes in the light and protein synthesis in the dark. These actinobacterial strains have the ability to sense light and possibly utilize the byproducts of photosynthesis released by primary producers for growth. Since they are ubiquitous in freshwater ecosystems, this makes them model organisms to study the energy flow from primary producers to consumers and study the physiological effect sunlight has on these heterotrophic bacteria.
Sunlight is a consistent stimulus in the environment– it is known that prokaryotes and eukaryotes depend on sunlight as a source of energy or have evolved biological clocks, which organize their physiological activities in accordance with the solar cycle 1,2.
In a nutrient-limited environment, sunlight is an unlimited resource. The conversion of sunlight to energy is well understood in photoautotrophs and photoheterotrophs. Light regulates the circadian rhythm in plants, animals and fungi, informing the organisms about the location and time. Therefore, light acts both as a source of energy and information. Here, we study three heterotrophic actinobacterial strains and their response to light. Actinobacteria are a phylum of Gram-positive bacteria, ubiquitous in freshwater. Three strains of Actinobacteria were isolated from different parts of the world: Rhodoluna(Rhl).
lacicola strain, Ta8 from Lake Taihu in China; Aurantimicrobiumsp. strain MWH-Mo1 from Lake Mondsee Austria and Microbacterium sp. strain 10M3C3 from Lake Matano in Indonesia 3.Rhl. lacicola and MWH-Mo1 are heterotrophs lacking a functional photosystem yet displayed a unique growth phenotype during the initial growth experiments: Rhl. lacicola and Mo1 exhibited increased growth in the light as compared to growth in the dark whereas 10M3C3 exhibited similar growth rates in the light and in the dark. This enhanced growth in the light was initially thought to be a result of existing photosystems. However, further experimentation4 revealed that both Rhl. lacicola and MWH-Mo1 lack a functional photosystem required for enhanced growth in light. We hypothesize that in Rhl. lacicolaand MWH-Mo1, that lack a functional photosystem to convert light to chemical energy, light acts as a cue resulting in changes in growth and transcription activities.
The three strains of Actinobacteria were isolated from different parts of the world: Rhodoluna(Rhl). lacicola strain, Ta8 from Lake Taihu in China; Aurantimicrobiumsp. strain MWH-Mo1 from Lake Mondsee Austria and Microbacterium sp. strain 10M3C3 from Lake Matano in Indonesia (Table 1)
In previous work conducted in the Maresca lab, RNA-seq analysis was performed on the actinobacterial strains Rhl. lacicol aand MWH-Mo1 to learn more about the transcriptional changes that result in the unique growth phenotype. The actinobacterial strains were grown till late exponential phase in continuous light and dark conditions and after quantifying the number of transcripts per gene, statistical data analysis was performed to learn if there existed a significant difference in the gene expression levels in the light and dark.