Dynamics of Heterotrophic Bacterial Assemblages within Synechococcus Cultures

Abstract

Interactions between photoautotrophic and heterotrophic microorganisms are central to the marine microbial ecosystem. Lab cultures of one of the dominant marine photoautotrophs, , have historically been difficult to render axenic, presumably because these bacteria depend upon other organisms to grow under these conditions. These tight associations between and heterotrophic bacteria represent a good relevant system to study interspecies interactions. Ten individual strains, isolated from eutrophic and oligotrophic waters, were chosen for investigation. Four to six dominant associated heterotrophic bacteria were detected in the liquid cultures of each isolate, comprising members of the -- (CFB) group (mainly from and), (mainly from the clade), (mainly from the and ), and The presence of the CFB group, , and showed clear geographic patterns related to the isolation environments of the bacteria. An investigation of the population dynamics within a growing culture (XM-24) of one of the isolates, including an evaluation of the proportions of cells that were free-living versus aggregated/attached, revealed interesting patterns for different bacterial groups. In sp. strain XM-24 culture, flavobacteria, which was the most abundant group throughout the culture period, tended to be aggregated or attached to the cells, whereas the actinobacteria demonstrated a free-living lifestyle, and roseobacters displayed different patterns depending on the culture growth phase. Factors contributing to these succession patterns for the heterotrophs likely include interactions among the culture community members, their relative abilities to utilize different compounds produced by cells and changes in the compounds released as culture growth proceeds, and their responses to other changes in the environmental conditions throughout the culture period. Marine microbes exist within an interactive ecological network, and studying their interactions is an important part of understanding their roles in global biogeochemical cycling and the determinants of microbial diversity. In this study, the dynamic relationships between spp. and their associated heterotrophic bacteria were investigated.-associated heterotrophic bacteria had similar geographic distribution patterns as their "host" and displayed different lifestyles (free-living versus attached/aggregated) according to the culture growth phases. Combined organic carbon composition and bacterial lifestyle data indicated a potential for succession in carbon utilization patterns by the dominant associated heterotrophic bacteria. Comprehending the interactions between photoautotrophs and heterotrophs and the patterns of organic carbon excretion and utilization is critical to understanding their roles in oceanic biogeochemical cycling.

Molecular characteristics of microbially mediated transformations of Synechococcus‐derived dissolved organic matter as revealed by incubation experiments

“…Near‐surface water samples (27.6°C) were collected from the South China Sea near Yongxing Island (~17° N, ~112° E) in April 2018 for incubation inocula. The sea water in this area is oligotrophic, with PO 4 3− and NO 3 − concentrations below 0.1 μM (Zheng et al ., ). Seawater was pre‐filtered with a 20‐μm pore size filter to remove eukaryotic cells, and then maintained in the dark for three days prior to DOM addition experiments.…”

“…The isolate Synechococcus sp. YX04‐3 was obtained from ocean waters near Yongxing Island in the South China Sea (Zheng et al ., ), which was also the location of the subsequent DOM addition experiments. Synechococcus cells grown to exponential phase were collected by centrifugation.…”

Metagenomic and Metaproteomic Insights into Photoautotrophic and Heterotrophic Interactions in a Synechococcus Culture

“…The lifestyles and genomic characteristics of dominant heterotrophic bacteria associated with coastal Synechococcus sp. strain XM-24 cultures have been investigated in detail, but the associated heterotrophs also show geographic distribution patterns that are related to the environments of Synechococcus strain isolation (25,26). Thus, several important aspects of these relationships remain unclear including (i) how open ocean Synechococcus culture ecotypes interact with their associated heterotrophic bacteria, (ii) how different heterotrophic bacterial populations interact with single cyanobacterial strains in coculture systems, and (iii) the nature of the roles of major bacterial populations in the Synechococcus culture systems.…”

The evolution of realized niches within freshwater Synechococcus

“…Recently, Zheng et al . (), observed a geographical pattern of heterotrophic bacteria associated with different marine Synechococcus strains, indicating that strains living in the same area tend to be associated with similar communities. It remains, however, unclear whether the Synechococcus genotype or the environment is the main drivers of Synechococcus interactions with the surrounding microbial community.…”

“…Previous studies have shown that different Synechococcus strains could co-exist in the same site but respond differently to environmental changes, suggesting niche partitioning (Ferris et al, 2003;Allewalt et al, 2006;Becker et al, 2007;Becraft et al, 2011;Callieri et al, 2012). Recently, Zheng et al (2018), observed a geographical pattern of heterotrophic bacteria associated with different marine…”