Unveiling interactions mediated by B vitamins between diatoms and their associated bacteria from cocultures.

Unveiling the interactions among phytoplankton and bacteria at the level of species requires axenic isolates to experimentally demonstrate their mutual effects. In this study, we describe the interactions among the diatoms Pseudo-nitzschia granii and Chaetoceros tenuissimus and their associated bacterial species, isolated from surface water of a coastal upwelling system using coculture experiments. Microalgae growth was assessed in axenic monocultures or in coculture with each of their co-isolated bacteria in the presence or absence of B vitamins.

Linking the impact of bacteria on phytoplankton growth with microbial community composition and co-occurrence patterns.

The interactions between microalgae and bacteria have recently emerged as key control factors which might contribute to a better understanding on how phytoplankton communities assemble and respond to environmental disturbances. We analyzed partial 16S rRNA and 18S rRNA genes from a total of 42 antibiotic bioassays, where phytoplankton growth was assessed in the presence or absence of an active bacterial community. A significant negative impact of bacteria was observed in 18 bioassays, a significant positive impact was detected in 5 of the cases, and a non-detectable effect occurred in 19 bioassays.

Role of Bacterial Community Composition as a Driver of the Small-Sized Phytoplankton Community Structure in a Productive Coastal System.

We present here the first detailed description of the seasonal patterns in bacterial community composition (BCC) in shelf waters off the Ría de Vigo (Spain), based on monthly samplings during 2 years. Moreover, we studied the relationship between bacterial and small-sized eukaryotic community composition to identify potential biotic interactions among components of these two communities. Bacterial operational taxonomic unit (OTU) richness and diversity systematically peaked in autumn-winter, likely related to low resource availability during this period.