Alginate and the acetylated sodium alginate are the predominant polysaccharides found in brown macroalgae [1] and biofilm of Pseudomonas aeruginosa, respectively, which encompass two isomer residues: β-D-mannuronic acid (M) and α-L-guluronic acid (G), resulting in the formation of polyM, polyG, polyMG blocks [2]. Alginate extracted from P. aeruginosa shows acetylation of the C2/C3 position on the M fragment to form acetylated sodium alginate [3], which was designed to prevent the activity of epimerase [4], and at the same time, the presence of acetylated sodium alginate can enhance the ability to evade the immune system and diminish its susceptibility to antibiotics, further restricting drug diffusion and rendering a range of antibiotics resistant to it [5]. Both types of alginates can be degraded enzymatically by alginate lyases, which generate a collection of size-determined oligosaccharide fragments or unsaturated monosaccharide, showing multiple biologically active capabilities such as anti-inflammatory, immune enhancement, metabolic system regulation and antioxidation [6]. Generally, alginate lyase is a polysaccharide lyase that degrades the 1→4 glycoside bond through a β-elimination reaction [7]. Despite the fact that hundreds of alginate lyases have been characterized, these enzymes are severely constrained by a number of factors, including inadequate activity and poor stability, which in turn impedes the subsequent application. In order to overcome these shortcomings, there is an urgent need for the discovery of alginate lyases with the best properties required for industrial applications (e.g., pH stability, heat resistance, and acid and alkali resistance). Cold-adapted enzymes, for example, can catalyze reactions at low temperatures and manage the reaction process easily, whereas acid and base resistant enzymes can catalyze reactions under extreme conditions and lower manufacturing costs. Thus, it is necessary to search for stable alginate lyases.

In terms of application, alginate lyases have revealed a wide range of applications. At present, alginate lyase is not only used in biofuels, but also has an essential effect on the removal of biofilm produced by P. aeruginosa. P. aeruginosa is a common conditional pathogen in our daily life and natural environment posing a serious danger to human health across the world [8], [9]. Biofilm, a significant issue of P. aeruginosa, is composed of complex aggregation of cells living in an exopolymeric matrix, and the acetylated sodium alginate is one of the main extracellular polysaccharide elements, in charge of attachment and bio-membrane stability to withstand antibiotic [10], resulting in recurrence of the diseases.

As a novel strategy for eradicating bacterial biofilms, there has been renewed interest in the enzymatic degradation for biofilm targeting strategy. Data from several studies correspondingly proved the possibility of several alginate lyases to suppress the P. aeruginosa biofilm development. Mahajan et al. [11] confirmed the biofilm inhibition of P. aeruginosa clinical strains with alginate lyase and in vitro co-culture model was also proved for its biofilm inhibitory effect. An observation in 2021 [12] has indicated that alginate lyase AlyP1400 could biodegrade alginate produced from P. aeruginosa strain CF27 and break down well-established biofilm in a dose-dependent manner.

In view of the lack of highly stable alginate lyases and the promising applications and therapy capacity of alginate lyases in infections caused by P. aeruginosa biofilms, a novel alginate lyase AlyG2 with high stability from Seonamhaeicola algicola was expressed and characterized, exhibiting distinctive properties significantly different from several alginate lyases, especially its various aspects of high stability, such as the broad pH adaptability, higher salt tolerance and the ability to withstand low temperature. At the same time, the effectiveness of genetically engineered enzyme as anti-biofilm against the food pathogen P. aeruginosa was constructed and evaluated. This article provides another new alginate lyase of subfamily 6 in PL7 and contributes to further observations on the anti-biofilm effect of alginate lyase on P. aeruginosa.