# Microbial Responses to Micronutrient Amendments in Oxygenated and Deoxygenated Waters of the Arabian Sea

## TL;DR

This study shows how adding micronutrients like zinc, iron, and cobalt affects microbial communities and nutrient levels in oxygen-rich and oxygen-poor waters of the Arabian Sea.

## Contribution

The study reveals how micronutrient amendments interact with oxygen conditions to alter microbial diversity and nutrient cycling in marine environments.

## Key findings

- Iron amendments increased microbial diversity and total bacterial counts most in oxygenated waters.
- Mixed micronutrient treatments had the strongest effect on microbial dynamics in deoxygenated waters.
- Micronutrient amendments significantly altered nutrient concentrations at both depths.

## Abstract

Metalloenzyme cofactors and oxygen conditions are crucial for microbial metabolism, yet their combined effects on microbial ecosystems remain unexplored. This study explores the impact of micronutrient amendments (Zn, Fe, Co and their combinations) on the microbial community composition in oxygenated (73 m) and deoxygenated (200 m) waters of the Arabian Sea. Through controlled microcosm experiment and 16S rRNA amplicon sequencing, we observed that micronutrients significantly alter nutrient concentrations and microbial dynamics. At 73 m, micronutrient treatments reduced nitrate, nitrite and ammonia levels, whereas at 200 m, they increased nitrate and silicate levels. Total bacterial counts (TBCs) were higher in all treatments at both depths, with Fe showing the highest counts. Alpha diversity indicated that Fe‐amended flask increased microbial diversity the most at 73 m, while mixed treatments had a pronounced effect at 200 m. Taxonomic analysis revealed significant genus‐level variations in both bacteria and archaea. One‐way analysis of variance (ANOVA) confirmed micronutrient impacts on nutrients and TBC. Canonical correspondence analysis (CCA) and non‐metric multidimensional scaling (NMDS) revealed distinct clustering based on oxygen conditions. These results confirm our hypothesis that micronutrient amendments in varying oxygen levels distinctly alter microbial community composition and nutrient cycling in marine environments.

Microcosm experiments and 16S rRNA amplicon sequencing show that micronutrients (Zn, Fe, Co) or their combination (Zn + Fe + Co) significantly influence nutrient concentrations and microbial dynamics in both oxygenated (73 m) and deoxygenated (200 m) waters of the Arabian Sea. Our findings highlight that Fe is particularly impactful, enhancing microbial diversity and total bacterial counts, especially in oxygenated conditions, while mixed micronutrient treatments had the most significant effects in deoxygenated depth.