Abstract
Marine bacteria employ various strategies to maintain their competitive advantage over others in a mixed community. The use of Type VI Secretion Systems (T6SS), a protein secretion apparatus used as a molecular weapon for interbacterial competition and eukaryotic interactions, is one of the competitive strategies that is least studied among heterotrophic bacteria living in the water column. To get an insight into the temporal and spatial distribution of bacteria with T6SS in this portion of the marine environment, we examine the presence and abundance of T6SS-bearing bacteria at both local and global scales through the use of metagenome data from water samples obtained from the coast of Monterey Bay and the TARA Oceans project. We also track the abundance of T6SS-harboring bacteria through a two-year time series of weekly water samples in the same coastal site to examine the environmental factors that may drive their presence and abundance. Among the twenty-one T6SS-bearing bacterial genera examined, we found several genera assume a particle-attached lifestyle, with only a few genera having a free-living lifestyle. The abundance of T6SS-harboring bacteria in both niches negatively correlates with the abundance of autotrophs. Globally, we found that T6SS genes are much more abundant in areas with low biological productivity. Our data suggest that T6SS-harboring bacteria tend to be abundant spatially and temporally when organic resources are limited. This ecological study agrees with the patterns observed from several in vitro studies; that T6SS could be an adaptive strategy employed by heterotrophic bacteria to obtain nutrients or reduce competition when resources are in limited quantity.
Highlights
Marine bacteria constitute the largest portion of biomass in the world’s oceans [1, 2] and are responsible for the cycling and regeneration of nutrients throughout the ocean [3]
These 21 genera belonging to classes Planctomycetia (Planctomyces), Alpha-proteobacteria (Bradyrhizobium, Mesorhizobium, Methylobacterium, Agrobacterium, Ruegeria, Rhodobacter, Sphingomonas), Beta-proteobacteria (Janthinobacterium), Epsilon-bacteria (Arcobacter), and Gamma-Proteobacteria (Acinetobacter, Enterobacter, Francisella, Halomonas, Pseudoalteromonas, Pseudomonas, Psychromonas, Serratia, Shewanella, Teredinibacter, Vibrio) made up the T6SS-harboring bacterial populations that were tracked in our subsequent study
We investigated the presence and abundance of bacteria with T6SS in a local coastal environment and the distribution of these populations in the global ocean to understand their
Summary
Marine bacteria constitute the largest portion of biomass in the world’s oceans [1, 2] and are responsible for the cycling and regeneration of nutrients throughout the ocean [3]. Most regenerated primary production relies on nutrients that pass through the microbial loop, whereby bacteria and other microorganisms metabolize organic compounds and return them to non-organic, bioavailable forms [4]. Abundance of T6SS-harboring bacteria in the pelagic environment
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