Very few studies have attempted to profile the microbial communities in the air above freshwater bodies, such as lakes, even though freshwater sources are an important part of aquatic ecosystems and airborne bacteria are the most dispersible microorganisms on earth. In the present study, we investigated microbial communities in the waters of two high mountain sub-alpine montane lakes—located 21 km apart and with disparate trophic characteristics—and the air above them. Although bacteria in the lakes had locational differences, their community compositions remained constant over time. However, airborne bacterial communities were diverse and displayed spatial and temporal variance. Proteobacteria, Actinobacteria, Bacteroidetes, and Cyanobacteria were dominant in both lakes, with different relative abundances between lakes, and Parcubacteria (OD1) was dominant in air samples for all sampling times, except two. We also identified certain shared taxa between lake water and the air above it. The results obtained on these communities in the present study provide putative candidates to study how airborne communities shape lake water bacterial compositions and vice versa.

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9Microbial communities have long been assumed to have functional redundancy, but very few 2 0 studies have tested this empirically. Here, we performed a time series in situ reciprocal transplant 2 1 experiment in two lakes with disparate trophic states to empirically test for functional 2 2 redundancy. We determined that the two lakes had different community compositions, and these 2 3 did not change even after incubating in a different environment. However, functional attributes 2 4were different between read-and predicted gene-level analyses of the communities, highlighting 2 5 the importance of resolution when delineating community functional relationships. Furthermore, 2 6there was a linear relationship between community composition and functional attributes, with a 2 7 broad range of similarities in the former and a narrower range and overall more similarity in the 2 8 latter, providing support for partial functional redundancy. Ecoplate analysis suggests that the 2 9 total metabolic activity of a community is influenced by its local environment, even though 3 0 broad functions like carbon metabolism are widespread. Together, our results support the 3 1 presence of resolution-dependent partial functional redundancy in aquatic environments. 3 2

To understand the immunity determinants of bacteriophage cf, we applied DNA shuffling to mutate the intergenic region (IG) for isolation of possible cf immunity mutants. After superinfection screening, an immunity mutant cf-m3 was obtained with a 106-109 fold greater superinfection ability compared with wild type cf. Nine mutations were characterized, four located within the coding region for a hypothetical repressor, PT gene (ORF165), and five located upstream of the PT coding region. To establish whether the major immunity determinant is the predicted PT protein or in the cis region, phage cf-ls-P and cf-ls-R were generated which showed as low superinfection efficiency as the wild type cf and had no superinfection ability on the cf-lysogen, respectively. This result indicates that rather than superinfection inhibition, the PT protein and the un-transcribed cis element function individually as positive regulators for cf superinfection immunity. Greater superinfection ability depends on the simultaneous presence of both elements. To learn more about the regulation of cf immunity, we characterized in silico the wild-type genome of cf (NCBI NC_001396) and the 61 non-redundant clustered regularly interspaced short palindromic repeats (CRISPR) spacers of Xanthomonas citri identified from 643 CRISPR spacers of 28 strains in the CRISPR database. No homology between CRISPR spacers and the cf genome was found. This indicates that the cf acts through a different immunity mechanism from the CRISPR system. This work yields further insight into the mechanism of cf superinfection immunity.