Investigating the Diversity of Marine Bacteriophage in Contrasting Water Masses Associated with the East Australian Current (EAC) System

Community Structure, Drivers, and Potential Functions of Different Lifestyle Viruses in Chaohu Lake

Viruses, as the most prolific entities on Earth, constitute significant ecological groups within freshwater lakes, exerting pivotal ecological roles. In this study, we selected Chaohu Lake, a representative eutrophic freshwater lake in China, as our research site to explore the community distribution, driving mechanisms, and potential ecological functions of diverse viral communities, the intricate virus-host interaction systems, and the overarching influence of viruses on global biogeochemical cycling.

Exploring virus-host-environment interactions in a chemotrophic-based underground estuary

BACKGROUND

Viruses play important roles in modulating microbial communities and influencing global biogeochemistry. There is now growing interest in characterising their ecological roles across diverse biomes. However, little is known about viral ecology in low-nutrient, chemotrophic-based environments. In such ecosystems, virus-driven manipulation of nutrient cycles might have profound impacts across trophic levels. In particular, anchialine environments, which are low-energy underground estuaries sustained by chemotrophic processes, represent ideal model systems to study novel virus-host-environment interactions.

RESULTS

Here, we employ metagenomic sequencing to investigate the viral community in Bundera Sinkhole, an anchialine ecosystem rich in endemic species supported by microbial chemosynthesis. We find that the viruses are highly novel, with less than 2% representing described viruses, and are hugely abundant, making up as much as 12% of microbial intracellular DNA. These highly abundant viruses largely infect important prokaryotic taxa that drive key metabolic processes in the sinkhole. Further, the abundance of viral auxiliary metabolic genes (AMGs) involved in nucleotide and protein synthesis was strongly correlated with declines in environmental phosphate and sulphate concentrations. These AMGs encoded key enzymes needed to produce sulphur-containing amino acids, and phosphorus metabolic enzymes involved in purine and pyrimidine nucleotide synthesis. We hypothesise that this correlation is either due to selection of these AMGs under low phosphate and sulphate concentrations, highlighting the dynamic interactions between viruses, their hosts, and the environment; or, that these AMGs are driving increased viral nucleotide and protein synthesis via manipulation of host phosphorus and sulphur metabolism, consequently driving nutrient depletion in the surrounding water.

CONCLUSION

This study represents the first metagenomic investigation of viruses in anchialine ecosystems, and provides new hypotheses and insights into virus-host-environment interactions in such 'dark', low-energy environments. This is particularly important since anchialine ecosystems are characterised by diverse endemic species, both in their microbial and faunal assemblages, which are primarily supported by microbial chemosynthesis. Thus, virus-host-environment interactions could have profound effects cascading through all trophic levels.

Isolation and Characterisation of the Bundooravirus Genus and Phylogenetic Investigation of the Salasmaviridae Bacteriophages

Bacillus is a highly diverse genus containing over 200 species that can be problematic in both industrial and medical settings. This is mainly attributed to Bacillus sp. being intrinsically resistant to an array of antimicrobial compounds, hence alternative treatment options are needed. In this study, two bacteriophages, PumA1 and PumA2 were isolated and characterized. Genome nucleotide analysis identified the two phages as novel at the DNA sequence level but contained proteins similar to phi29 and other related phages. Whole genome phylogenetic investigation of 34 phi29-like phages resulted in the formation of seven clusters that aligned with recent ICTV classifications. PumA1 and PumA2 share high genetic mosaicism and form a genus with another phage named WhyPhy, more recently isolated from the United States of America. The three phages within this cluster are the only candidates to infect B. pumilus. Sequence analysis of B. pumilus phage resistant mutants revealed that PumA1 and PumA2 require polymerized and peptidoglycan bound wall teichoic acid (WTA) for their infection. Bacteriophage classification is continuously evolving with the increasing phages' sequences in public databases. Understanding phage evolution by utilizing a combination of phylogenetic approaches provides invaluable information as phages become legitimate alternatives in both human health and industrial processes.

Microbial tropicalization driven by a strengthening western ocean boundary current

Western boundary currents (WBCs) redistribute heat and oligotrophic seawater from the tropics to temperate latitudes, with several displaying substantial climate change-driven intensification over the last century. Strengthening WBCs have been implicated in the poleward range expansion of marine macroflora and fauna, however, the impacts on the structure and function of temperate microbial communities are largely unknown. Here we show that the major subtropical WBC of the South Pacific Ocean, the East Australian Current (EAC), transports microbial assemblages that maintain tropical and oligotrophic (k-strategist) signatures, to seasonally displace more copiotrophic (r-strategist) temperate microbial populations within temperate latitudes of the Tasman Sea. We identified specific characteristics of EAC microbial assemblages compared with non-EAC assemblages, including strain transitions within the SAR11 clade, enrichment of Prochlorococcus, predicted smaller genome sizes and shifts in the importance of several functional genes, including those associated with cyanobacterial photosynthesis, secondary metabolism and fatty acid and lipid transport. At a temperate time-series site in the Tasman Sea, we observed significant reductions in standing stocks of total carbon and chlorophyll a, and a shift towards smaller phytoplankton and carnivorous copepods, associated with the seasonal impact of the EAC microbial assemblage. In light of the substantial shifts in microbial assemblage structure and function associated with the EAC, we conclude that climate-driven expansions of WBCs will expand the range of tropical oligotrophic microbes, and potentially profoundly impact the trophic status of temperate waters.