Looking Outwards: Isolation of Cyanobacterial Released Carbohydrate Polymers and Proteins

Summary

Here, protocols for the isolation of cyanobacterial released carbohydrate polymers and isolation of their exoproteomes are described. Both procedures embody key steps to obtain polymers or proteins with high purity degrees that can be used for further analysis or applications. They can also be easily adapted according to specific user needs.

Abstract

Cyanobacteria can actively secrete a wide range of biomolecules into the extracellular environment, such as heteropolysaccharides and proteins. The identification and characterization of these biomolecules can improve knowledge about their secretion pathways and help to manipulate them. Furthermore, some of these biomolecules are also interesting in terms of biotechnological applications. Described here are two protocols for easy and rapid isolation of cyanobacterial released carbohydrate polymers and proteins. The method for isolation of released carbohydrate polymers is based on conventional precipitation techniques of polysaccharides in aqueous solutions using organic solvents. This method preserves the characteristics of the polymer and simultaneously avoids the presence of contaminants from cell debris and culture medium. At the end of the process, the lyophilized polymer is ready to be used or characterized or can be subjected to further rounds of purification, depending on the final intended use. Regarding the isolation of the cyanobacterial exoproteome, the technique is based on the concentration of the cell-free medium after removal of the major contaminants by centrifugation and filtration. This strategy allows for reliable isolation of proteins that reach the extracellular milieu via membrane transporters or outer membrane vesicles. These proteins can be subsequently identified using standard mass spectrometry techniques. The protocols presented here can be applied not only to a wide range of cyanobacteria, but also to other bacterial strains. Furthermore, these procedures can be easily tailored according to the final use of the products, purity degree required, and bacterial strain.

Introduction

Cyanobacteria are widely recognized as prolific sources of natural products with promising biotechnological/biomedical applications. Therefore, understanding cyanobacterial secretion mechanisms and optimization of the extraction/recovery methods are essential to implement cyanobacteria as efficient microbial cell factories.

Many cyanobacterial strains are able to produce extracellular polymeric substances (EPS), mainly formed by heteropolysaccharides, that remain associated to the cell surface or are released into the medium¹. These released carbohydrate polymers have distinct features compared to those from other ba....

Protocol

1. Cyanobacterial released carbohydrate polymer isolation

1. Polymer isolation and removal of contaminants
   1. Cultivate the cyanobacterial strain under standard conditions [e.g., 30 °C under a 12 h light (50 μE m⁻²s⁻¹)/12 h dark regimen, with orbital shaking at 150 rpm]. Measure growth using standard protocols [e.g., optical density at 730 nm (OD_730nm), chlorophyll a, dry-weight, etc.], then measure the production of relea.......

Discussion

To better understand bacterial secretion mechanisms and study the released products, it is of extreme importance to demonstrate the efficient isolation and analysis of the biomolecules present in the extracellular bacterial environment (such as released carbohydrate polymers and proteins).

Cyanobacterial extracellular carbohydrate polymers are extremely complex, mainly due to the number and proportion of different monosaccharides that constitute their composition¹. The .......

Materials

Name	Company	Catalog Number	Comments
Dialysis membranes	Medicell Membranes Ltd	DTV.12000.07	Visking Tubing Size 7, Dia 23.8 mm, Width 39-41 mm 30m Roll
Ethanol 96%	AGA - Álcool e Géneros Alimentares, S.A.	4.000.02.02.00	Fermentation ethyl alcohol 96% AGA
PES Filter 0.2 μm	Fisher Scientific, Lda	15206869	Syringe filter polystyrene 33MM 0.2µM STR
Amicon Ultra-15, Ultracel-3K	Merck Millipore Ltd.	UFC900324	Centrifugal filters with a nominal molecular weight cut-off of 3 kDa
Thermo Scientific Pierce BCA Protein Assay	Fisher Scientific, Lda	10741395	Green-to-blue, precise, detergent-compatible assay reagent to measure total protein concentration
Brillant Blue G Colloidal Concentrate	Sigma Aldrich Química SL	B2025-1EA	Coomassie blue