Response of prokaryote community composition to riverine and atmospheric nutrients in a coastal embayment: role of organic matter on Vibrionales

Abstract

The responses of coastal microbial communities to nutrient inputs depend on the magnitude and nature of those inputs. To understand the response of prokaryote communities to contrasting levels of nutrient inputs from different sources, three nutrient addition experiments were performed in the Ría de Vigo in spring, summer, and autumn. The experiments consisted of controlled inorganic (nitrate, ammonium and phosphate), organic (glucose and a mix of 18 amino acids), and mixed (inorganic and organic); as well as natural (atmospheric and riverine) nutrient additions to surface water samples taken from the middle of the embayment and incubated for 48h, under in situ temperature and irradiance conditions. Prokaryote community DNA was collected and analyzed using high-throughput amplicon sequencing of the 16S rRNA gene. The joint addition of inorganic and organic nutrients provoked the most pronounced changes in community composition, systematically leading to great increases in the proportion of sequence reads belonging to Vibrionales, while natural amendments only caused subtle alterations. The proportion of reads assigned to the Planktomarina genus, bacteria belonging to the order Rhodobacterales, tended to increase when natural atmospheric nutrients were added. Overall, the fraction of reads belonging to the order Flavobacteriales did not show relevant changes, although the contribution of sequences affiliated to Polaribacter and Aurantivirga genera increased after atmospheric and riverine inputs in summer, and autumn. The proportion of Vibrionales reads also increased after controlled organic amendments in autumn, and to a lesser extent after riverine additions in spring and summer. In general, our findings suggest that an increasing input of nitrogenous organic matter from allochthonous sources into this coastal environment might promote the growth of potentially pathogenic bacteria belonging to the order Vibrionales.