Investigating exudate- and habitat-mediated effects of phytoplankton on lake bacterial community dynamics

Correlated patterns of abundance, activity, and composition are commonly observed between phytoplankton and bacterial communities. There are a number of potential explanations for correlated dynamics. Recent observations of temporal succession in lake microbial communities provide evidence for phytoplankton populations acting as biological drivers structuring bacterial communities. The following thesis addresses two potentially important connections between phytoplankton and bacteria: resource-mediated linkage through production of labile carbon exudates and habitat-mediated linkage. To investigate phytoplankton exudates as a potential linkage, the first investigation focused on bacteria able to use the photorespiration-specific exudate glycolate. Diversity and dynamics of glycolate-utilizing bacteria were characterized in six lakes using functional gene glycolate oxidase subunit D (glcD). Freshwater glycolate-utilizing populations exhibited a range of taxonomic diversity and contained many sequences clustering with a glcD sequence from the cosmopolitan freshwater Polynucleobacter genus. Glycolate-utilizing and total bacterial community-level variation was largely explained by dynamics of phytoplankton populations (35-40%) and the interaction between these phytoplankton populations and the environment (17-18%). Population-level correlations between specific phytoplankton and glycolate-utilizing bacteria were also detected. These observations support the hypothesis that algal exudates are resource-based drivers of bacterial community composition and identify bacterial taxonomic groups with members capable of responding directly to a specific exudate. Contribution of epiphytic bacteria inhabiting algal cells to correlated community dynamics was investigated by comparing temporal community patterns in the particle-associated bacteria to those of whole bacteria and phytoplankton in Crystal and South Sparkling Bogs. Regular patterns of succession, in addition to correlations between phytoplankton and whole bacterial communities (ρ=0.514, p=0.001) and phytoplankton and particle-associated bacterial communities (ρ=0.739, p=0.001), were detected in Crystal, but not South Sparkling Bog (ρ=0.265, p=0.038; ρ=0.167, p=0.103, respectively). Attached and free-living bacterial assemblages were compared to classify bacterial taxa based on presence in attached and/ or free-living fractions. Despite mixed results for community-level correlations, bacterial populations were positively correlated to abundance of specific phytoplankton in both lakes. Algal-correlated bacteria ranged from primarily particle-associated bacteria in Crystal Bog to a mix of particle-associated and free-living bacteria in South Sparkling Bog. These observations provide support for habitat-mediated linkages, while also indicating the importance of other mechanisms that affect free-living and habitat generalist populations. Taken together, these investigations contribute to a growing body of research demonstrating the importance of biological interactions in shaping microbial community structure. Microbial community composition and function have implications for energy flow, carbon flux, and biogeochemical transformations with ecosystem-level consequences. Understanding biological interactions that structure bacterial communities may facilitate the building of a predictive framework for understanding compositional and functional responses of bacteria and microbially-mediated processes to changing environmental conditions

Covering of elliptic curves and the kernel of the Prym map

Motivated by a conjecture of Xiao, we study families of coverings of elliptic curves and their corresponding Prym map $\Phi$. More precisely, we describe the codifferential of the period map $P$ associated to $\Phi$ in terms of the residue of meromorphic $1$-forms and then we use it to give a characterization for the coverings for which the dimension of $\ker(dP)$ is the least possibile. This is useful in order to exclude the existence of non isotrivial fibrations with maximal relative irregularity and thus also in order to give counterexamples to the Xiao's conjecture mentioned above. The first counterexample to the original conjecture, due to Pirola, is then analysed in our framework.Comment: 21 pages, no figures. The seminal ideas at the base of this article were born in the framework of the PRAGMATIC project of year 201

Securing a business loan : how important is gender

This report examines the role of gender in business and evalates whether there is a evidence of gender bias when it comes to securing bank loans

Twin-waves propagation phenomena in magnetically-coupled structures

The use of magnetic dipoles embedding in an elastic support introduces long-range interaction forces. This is a completely new paradigm in structural mechanics, classically based on local short-range particle interaction. The features of long-range forces produce very new mechanical coupling effects. This paper examines the case in which two identical rod-like structures, each with a dipole distribution embedded, vibrate side by side. Waves generated in one of the rods propagate also in the second and vice versa creating a new effect we name twin-waves. The present investigation unveils the existence of an infinite number of propagation modes even in one-dimensional infinite structures, a new and unus al behaviour in classical waveguides. The physics behind this phenomenon is further investigated also by numerical simulations