Investigating the Microbial Communities Associated with Aluminum Alloys 2024 and 7075

Abstract

Aluminum (Al), one of the most versatile, cost-effective, and appealing metals for use in construction, has no known biological function. Al alloys in aquatic environments provide a surface for attachment and can be advantageous for nutrient acquisition. Due to Al's toxicity, there is little competition for colonizing the surface of Al alloys; therefore, organisms that survive in these conditions have an advantage over others that cannot. Previous research on the microbial communities that attach to a variety of surfaces like copper, Al, steel alloys, and plastics has shown that they are unique in composition and that certain community members may be preferentially selecting the surfaces they attach to. Because of this, I hypothesized that the microbial communities attached to Al alloys will be different than those attached to other metal alloys and surface materials. This will then be evident by variation in the microbial community composition between the substrates. To test this hypothesis, a field-based environmental study was conducted at two locations in the Pamlico River in North Carolina for 8 months investigating the microbial communities that colonize different substrates of interest--Al alloys 2024 & 7075, stainless steel alloys 304 & 316, a non-metal biofouling plate, and sediment. After 6-8 weeks, DNA was extracted from the material attached to the metal coupons and the microbial community was sequenced via 16S rRNA gene amplicon Illumina sequencing. Results suggest the microbial communities attached to all substrates were more similar in July than December. Salinity and water temperature were found to drive the variation in community composition. Gammaproteobacteria were found to primarily contribute to the dissimilarity between Al 2024 and Al 7075, with a higher abundance on Al 2024. Using the biomass attached to the Al alloys, Bacillus and Pseudoalteromonas sp. were isolated from Al 2024 in the presence of aluminum. The isolate's growth limits were characterized to further understand the microorganisms that attach to Al surfaces and how they are able to withstand changes in the environment in the presence of Al. I hypothesized that decreasing the temperature below the isolate's optimal growth temperature would negatively affect its tolerance to aluminum. Results suggest that isolates from Al 2024 in an estuary environment are negatively affected by a 5C drop in temperature at 1 mM AlCl3, as their maximum optical density at 600 nm decreased. These findings can be used to understand the variation in microbial communities attached to Al 2024 in estuaries globally, and ultimately to develop specialized management strategies to preserve Al alloy infrastructure in aquatic systems.