Biology subjects

Goetsch, A. G.

Publications and source records attributed to Goetsch, A. G..

4 recordsLinked to original sources

bioRxiv2026

Diversification of biofilm architecture among freshwater Pararheinheimera isolates

Air-liquid interfaces (ALIs) at the upper layer of oceans, lakes and rivers cover the majority of the earths surface. Microbes are known to accumulate at these resource-rich boundaries, but the mechanisms of ALI colonization are often assumed to mirror the formation of pellicle biofilms by non-aquatic organisms. Here, we analyzed ALI colonization by natural aquatic bacteria. We used samples from a freshwater lake to enrich for microbes that colonize the ALI in liquid growth medium. Mixed-species pellicles formed rapidly in these enrichments, were structurally stable for weeks and displayed a pronounced ecological succession. We isolated 31 members of the genus Pararheinheimera from early stages of mixed-species pellicle maturation. Five phylogenetically distinct Pararheinheimera clades were identified, each with a shared colony morphology. We used representative isolates to show that only one Pararheinheimera clade formed thin, adherent films at the ALI resembling classical pellicles. Isolates from the four remaining clades formed floating structures that could be categorized either as non-adhesive films or large viscous masses. Viscous mass (VM) pellicle formation was a polyphyletic trait that correlated with a highly mucoid appearance on agar plates, suggesting that the process is driven by copious secretion of extracellular matrix. Matrices from VM biofilms were largely non-adhesive, contained a mixture of acidic polysaccharides and proteins and formed thermally stable, shear-thinning hydrogels. Our results demonstrate that ALI colonization strategies vary widely even among closely related aquatic bacteria and identify VM pellicles as a distinct biofilm architecture with unique mechanical properties. ImportanceLakes, rivers and oceans contain a boundary between the air and the waters surface known as the air-liquid interface (ALI). Microbial communities that populate the ALI play crucial roles in nutrient cycling, but how aquatic microbes partition to these sites remains poorly characterized. Our study investigated how bacteria from a freshwater lake accumulate at the ALI. Lake water samples incubated in nutrient medium formed a layer of cells known as a pellicle biofilm at the ALI, and we isolated 31 different bacteria from a genus (Pararheinheimera) that was abundant during the early stages of pellicle formation. Only a subset of Pararheinheimera isolates formed traditional pellicle biofilms. Most formed either thin, non-adhesive films or large, gelatinous aggregates that appeared to persist at the ALI due to buoyancy. These findings expand our understanding of biofilm diversity in aquatic systems and suggest that the production of buoyant hydrogels may play an important role in structuring microbial communities at air-water boundaries.

microbiology↗

bioRxiv2026

Rheinheimera sp. T2C2 Bacterial Biofilm for Bioremediation of Cobalt (II)

Toxic metals, including cobalt, are often the cause of contamination of rivers and lakes in mining regions. Heavy metal water pollution has been linked to numerous human health problems, prompting the need for environmental remediation. Existing techniques for removing heavy metals from water, such as chemical precipitation and filtration, produce toxic waste, are costly, or require high power consumption for pumping. Biosorption is a potential alternative strategy that is cost-effective and uses readily available and naturally produced biomass and living material to absorb pollutants. Engineering living materials, such as biofilms, which consist of living cells and a secreted polymer matrix, offer potential to integrate toxin sensing, sequestration, and metabolism capabilities of cells to improve pollution remediation strategies. New biofilm producing candidates need to be explored to implement these material capabilities. Previous biosorption studies have primarily used bacterial biofilms from known pathogens and/or generate toxic waste in the form of the absorbent material combined with the heavy metal. Here, we describe a newly isolated bacterium called Rheinheimera sp. T2C2 that forms biofilms with promising biosorption characteristics. T2C2 is a non-pathogenic, aquatic bacterium with low nutrient requirements and high biofilm production. We demonstrate 1) the efficacy of Rheinheimera sp. T2C2 as a biosorbent for cobalt bioremediation; 2) how biosorption is altered by water conditions to establish the efficacy of this strategy in different environments; and 3) how the metal can be released from the biofilm for metal recycling. Our findings will provide a living materials strategy that overcomes existing barriers for bioremediation, and improve the health of ecosystems and humans through heavy metal removal and recycling.

microbiology↗

bioRxiv2024

Engineering Bacterial Biomanufacturing: Characterization and Manipulation of Sphingomonas sp. LM7 Extracellular Polymers

Biologically produced materials are an attractive alternative to traditional materials such as metals and plastics and offer improved functionalities such as better biodegradability and biocompatibility. Polysaccharides are an example of a biologically produced materials that can have a range of chemical and physical properties including high stiffness to weight ratios and thermal stability. Biomanufactured bacterial polysaccharides can come with many advantages such as being non-toxic and are mechanically robust relative to proteins and lipids, which are also secreted by bacteria to generate a biofilm. One major goal in biomanufacturing is to produce quality material quickly and cost-effectively. Biomanufacturing offers additional benefits compared to traditional manufacturing including low resource investment and equipment requirements, providing an alternative to sourcing fossil fuel byproducts, and relatively low temperatures needed for production. However, many biologically produced materials require complex and lengthy purification processes before use. This paper 1) identifies the material properties of a novel polysaccharide, dubbed promonan, isolated from the extracellular polymeric substances of Sphingomonas sp. LM7; 2) demonstrates that these properties can be manipulated to suit specific applications; and 3) presents two alternative methods of processing to shorten purification time by more than 50% while maintaining comparable material.

biophysics↗

bioRxiv2023

A novel exopolysaccharide pathway from a freshwater Sphingomonas isolate

Bacteria embellish their cell envelopes with a variety of specialized polysaccharides. Biosynthesis pathways for these glycans are complex, and final products vary greatly in their chemical structures, physical properties and biological activities. This tremendous diversity comes from the ability to arrange complex pools of monosaccharide building blocks into polymers with many possible linkage configurations. Due to the complex chemistry of bacterial glycans, very few biosynthetic pathways have been defined in detail. To better understand the breadth of polysaccharide production in nature we isolated a bacterium from Lake Michigan called Sphingomonas sp. LM7 that is proficient in exopolysaccharide (EPS) production. We identified genes that contribute to EPS biosynthesis in LM7 by screening a transposon mutant library for colonies displaying altered colony morphology. A gene cluster was identified that appears to encode a complete wzy/wzx-dependent polysaccharide assembly pathway. Deleting individual genes in this cluster caused a non-mucoid phenotype and a corresponding loss of EPS secretion, confirming that LM7 assembles a novel wzy/wzx-dependent polysaccharide. We extracted EPS from LM7 cultures and showed that it contains a linear chain of 3- and 4-linked glucose, galactose, and glucuronic acid residues. Finally, we found that the EPS pathway we identified diverges from those of adhesive polysaccharides such as the holdfast that are conserved in higher Alphaproteobacteria. Our approach of characterizing complete biosynthetic pathways holds promise for engineering of polysaccharides with valuable properties. ImportanceBacteria produce complex polysaccharides that serve a range of biological functions. These polymers often have properties that make them attractive for industrial applications, but they remain woefully underutilized. In this work, we studied a novel polysaccharide called promonan that is produced by Sphingomonas sp. LM7, a bacterium we isolated from Lake Michigan. We extracted promonan from LM7 cultures and identified which sugars are present in the polymer. We also identified the genes responsible for polysaccharide production. Comparing the promonan genes to those of other bacteria showed that promonan is distinct from previously characterized polysaccharides. We conclude by discussing how the promonan pathway could be used to produce new polysaccharides through genetic engineering.

microbiology↗