Genomic Characterization of a Novel Freshwater Cyanophage Reveals a New Lineage of Cyanopodovirus

Cyanobacteria are one of the dominant autotrophs in tropical freshwater communities, yet phages infecting them remain poorly characterized. Here we present the characterization of cyanophage S-SRP02, isolated from a tropical freshwater lake in Singapore, which infects Synechococcus sp. Strain SR-C1 isolated from the same lake. S-SRP02 represents a new evolutionary lineage of cyanophage. Out of 47 open reading frames (ORFs), only 20 ORFs share homology with genes encoding proteins of known function. There is lack of auxiliary metabolic genes which was commonly found as core genes in marine cyanopodoviruses. S-SRP02 also harbors unique structural genes highly divergent from other cultured phages. Phylogenetic analysis and viral proteomic tree further demonstrate the divergence of S-SRP02 from other sequenced phage isolates. Nonetheless, S-SRP02 shares synteny with phage genes of uncultured phages obtained from the Mediterranean Sea deep chlorophyll maximum fosmids, indicating the ecological importance of S-SRP02 and its related viruses. This is further supported by metagenomic mapping of environmental viral metagenomic reads onto the S-SRP02 genome.

Nitrous Oxide Emission from a Flooded Tropical Wetland across a Vegetation and Land Use Gradient

Whereas wetland ecosystems are among the most vital natural carbon sinks, they are also important sources of nitrous oxide (N2O), a highly potent greenhouse gas. However, due to differences in wetland characteristics, N2O emission is likely to vary across wetland types. We investigated the: 1) influence of vegetation community (Typha latifolia; Typha, Phragmites mauritianus; Phragmites and Cyperus papyrus; Papyrus) in a natural tropical freshwater wetland, and 2) impact of converting a natural tropical freshwater wetland into a rice paddy wetland on N2O emission. Results showed that N2O emission (µg m− 2 h− 1) from the natural wetland did not vary significantly (p > 0.05) among the vegetation communities during both the dry and wet seasons (Typha = 0.6 ± 1.6 [SE] and 0.5 ± 1.4, Phragmites = 0.5 ± 1.7 and 0.4 ± 1.5, Papyrus = 0.5 ± 1.3 and 0.5 ± 1.5, respectively). These emission rates insignificantly differed (p > 0.05) from those recorded in the rice paddy wetland (dry season = 0.7 ± 2.8 and wet season = 0.6 ± 2.7). There was no significant correlation (p > 0.05) between soil physico-chemical characteristics and N2O emission. We concluded that vegetation community does not affect N2O emission from a natural tropical freshwater wetland under continuous flooding. Similarly, under continuous flooding and no fertilization conditions, converting a natural tropical freshwater wetland into a rice paddy wetland does not influence N2O emission. We roughly estimated total annual N2O emissions (T yr− 1) and their carbon dioxide equivalents (CO2e; T yr− 1) from all Uganda’s natural and rice paddy wetlands as: natural wetlands = 115.1 ± 342.8 (CO2e = 30,501.5 ± 90,842) and rice paddy wetlands = 0.9 ± 2.7 (CO2e = 242.5 ± 707.6).