Date of Award
12-20-2024
Date Published
January 2023
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Biology
Advisor(s)
Roy Welch
Keywords
Biofilm;Development;Myxococcus xanthus;Population dynamics;Sporulation;Streaming
Subject Categories
Life Sciences | Microbiology
Abstract
Myxococcus xanthus, a soil-dwelling bacterium, exhibits complex multicellular behaviors through self-organization into biofilms. M. xanthus cells traverse agar surfaces, forming either predatory biofilm or vegetative swarm that expands outward in the presence of nutrients. Upon nutrient depletion, the swarm reorganizes as cells “stream” inward, coalescing into aggregates that mature into spore-filled fruiting bodies. This starvation-induced biofilm development is a complex process, governed by stringent genetic controls and coordinated population interactions. Despite extensive research into the dynamics of this development, from the onset of starvation to fruiting body maturation, a comprehensive understanding is still missing. This dissertation sheds light on the population dynamics during the early and late stages of M. xanthus starvation-induced biofilm formation. In this study, we demonstrate that streaming, a multicellular behavior, is not essential for the initiation of nascent aggregates. By integrating four key features—cell movement, local alignment, local density, and stream persistence—we developed a stream detection mask applicable to various M. xanthus strains. The stream mask can pinpoint the location of streams, both in time and space. Our findings reveal that where an aggregate initiate does not depend on streams, which are randomly distributed rather than being concentrated around aggregates with higher probability. Furthermore, by examining strains deficient in either of the two motility systems, we established that streaming and aggregation are independent phenotypes. A mutant lacking adventurous motility formed aggregates without streaming, indicating a potential link between adventurous motility and streaming. The mutant deficient in streaming aggregated more slowly than the wild type, suggesting that streams might enhance aggregation efficiency by facilitating faster aggregation. Additionally, we investigated the population dynamics influencing sporulation phenotypes by varying aliquot volumes, comparing cell distribution of aliquots of equal volume placed in one large spot versus multiple smaller spots, and adjusting the proximity of cell spots in sporulation assays. We identified these parameters as optimizable for enhancing sporulation efficiency and reproducibility. Large aliquot volumes correlated with reduced spore recovery, likely due to a higher number of elongated aggregates. Distributing an equal number of cells into five smaller spots, compared to one large spot, resulted in a twofold increase in spore recovery. Testing spot proximity revealed a novel "1-3-5 effect," where spore recovery decreased with increasing spot distance up to 3.5 cm before increasing again. This phenomenon was observed among mutant strains as well and it required cells of the same genotype to be on the same agar surface. We hypothesize that a diffusible signal might be involved. Thus, in this thesis we provide significant insights into M. xanthus development, investigating the role of streaming in nascent aggregation and introducing new factors influencing sporulation efficiency. These findings enhance our understanding of M. xanthus development and offer valuable knowledge and tool applicable to various bacteria and amoebae capable of forming developmental biofilms.
Access
Open Access
Recommended Citation
Khan, Trosporsha Tasnim, "POPULATION DYNAMICS IN MYXOCOCCUS XANTHUS DEVELOPMENTAL BIOFILM" (2024). Dissertations - ALL. 2023.
https://surface.syr.edu/etd/2023