Ecological interactions between phytoplankton and bacteria control chemical cycling at the base of aquatic food webs making them fundamental in shaping ecosystem productivity. These relationships are governed by reciprocal exchanges of metabolites that can affect the growth of one or both partners. Among the chemical currencies involved in these exchanges, Plant Growth Promoting Hormones (PGPH) have been identified as important metabolites that bacteria can provide to phytoplankton, but we do not know which PGPH are the most effective at enhancing phytoplankton growth, and which bacterial associates are the largest provider of these compounds. Here, we determined the diversity and abundance of PGPH producing bacteria within the diatom Actinocyclus curvatulus microbiome and quantified the concentrations of PGPH they produce. Finally, we examined how the bacterial-derived PGPHs influence A. curvatulus growth. Our results demonstrate that axenic cultures A. curvatulus only produce low concentrations of Indole-3-butyric acid (IBA), Jasmonic acid (JA), and Indole-3-acetic acid (IAA). We isolated 14 different bacterial strains from A. curvatulus cultures, which all produced a suite of PGPH. In addition to IBA, IAA, and JA, pure bacterial cultures also produced Abscisic acid (ABA), Gibberellic acid (GA), Benzyl adenine (BA), Trans-zeatin (TZ) and Brassinolides (BN). Specifically, the Alphaproteobacteria Shimia thalassica, and Aliiroseovarius sp., as well as the Gammaproteobacteria Pseudoalteromonas phenolica produced the largest diversity of PGPH. Our results uncover the diversity of PGPH produced by A. curvatulus microbial communities and broadens our understanding of PGPH biosynthesis. We anticipate our research to be a starting point, highlighting the importance of PGPH in diatom-bacteria interactions.