Friends With Benefits: Exploring the Phycosphere of the Marine Diatom Skeletonema marinoi

Abstract

Marine diatoms are the dominant phytoplankton in the temperate oceans and coastal regions, contributing to global photosynthesis, biogeochemical cycling of key nutrients and minerals and aquatic food chains. Integral to the success of marine diatoms is a diverse array of bacterial species that closely interact within the diffusive boundary layer, or phycosphere, surrounding the diatom partner. Recently, we isolated seven distinct bacterial species from cultures of Skeletonema marinoi , a chain-forming, centric diatom that dominates the coastal regions of the temperate oceans. Genomes of all seven bacteria were sequenced revealing many unusual characteristics such as the existence of numerous plasmids of widely varying sizes. Here we have investigated the characteristics of the bacterial interactions with S. marinoi , demonstrating that several strains ( Arenibacter algicola strain SMS7, Marinobacter salarius strain SMR5, Sphingorhabdus flavimaris strain SMR4y, Sulfitobacter pseudonitzschiae strain SMR1, Yoonia vestfoldensis strain SMR4r and Roseovarius mucosus strain SMR3) stimulate growth of the diatom partner. Testing of many different environmental factors including low iron concentration, high and low temperatures, and chemical signals showed variable effects on this growth enhancement by each bacterial species, with the most significant being light quality in which green and blue but not red light enhanced the stimulatory effect on S. marinoi growth by all bacteria. Several of the bacteria also inhibited growth of one or more of the other bacterial strains to different extents when mixed together. This study highlights the complex interactions between diatoms and their associated bacteria within the phycosphere, and that further studies are needed to resolve the underlying mechanisms for these relationships and how they might influence the global success of marine diatoms.

Diatom modulation of select bacteria through use of two unique secondary metabolites

“…F10, and A. macleodii F12 from the natural diatom microbial consortium provides an ample prospect to better understand phytoplankton modulation of different bacterial taxa in the phycosphere. Sulfitobacter and Phaeobacter are considered beneficial bacteria to diatoms, dinoflagellates, and macroalgae as they provide a variety of essential nutrients and cofactors that confer metabolic advantage to their hosts ( 17 , 18 , 51 – 56 ). Remarkably, several S. pseudonitzschiae strains (16S rRNA gene sequence identity >97%) have been isolated from several diatom species originating from different oceanic regions ( 18 , 57 , 58 ).…”

Improved Reference Genome forCyclotella crypticaCCMP332, a Model for Cell Wall Morphogenesis, Salinity Adaptation, and Lipid Production in Diatoms (Bacillariophyta)

“…As small fragments, the origin and identity of these sequence fragments are especially challenging to characterize. Diatoms maintain intimate relationships with bacteria both in nature (Amin et al 2012) and in cell culture (Johansson et al 2019). In addition, some diatom genomes appear to contain bacterial-derived genes (Bowler et al 2008).…”

Whole Genome Sequence of Marinobacter salarius Strain SMR5, Shown to Promote Growth in its Diatom Host

“…In terms of strain SMR5's relationship with its host, enhanced growth of S. marinoi strain R05AC in the presence of excess strain SMR5 has been observed in culture 14. Based on examination of the annotation using Pathway Tools version 21.0 15, our current hypothesis is that this may be caused by the production of indole-3-acetic acid (auxin) by strain SMR5.…”