Biofilm formation and microbial adhesion are two related and complex phenomena. These phenomena are known to play an important role in microbial life and various functions with positive and negative aspects. Actinobacteria have wide distribution in aquatic and terrestrial ecosystems. This phylum is very large and diverse and contains two important genera Streptomyces and Mycobacteria. The genus Streptomyces is the most biotechnologically important, while the genus Mycobacteria contains the pathogenic species of Mycobacteriaceae. According to the literature, the majority of studies carried out on actinomycetes are focused on the detection of new molecules. Despite the well-known diversity and metabolic activities, less attention has been paid to this phylum. Research on adhesion and biofilm formation is not well developed. In the present review, an attempt has been made to review the literature available on the different aspects on biofilm formation and adhesion of Actinobacteria. We focus especially on the genus Streptomyces. Furthermore, a brief overview about the molecules and structures involved in the adhesion phenomenon in the most relevant genus is summarized. We mention the mechanisms of quorum sensing and quorum quenching because of their direct association with biofilm formation.
Streptomyces are known for their ability to produce various secondary metabolites used in biotechnology, human medicine and agriculture. Understanding of surface properties is very interesting in the control of interfacial phenomena. The objective of this study was to investigate the effect of consistency and composition of growth medium on the physicochemical properties of the surface of Streptomyces strains. To achieve this objective, Six Streptomyces strains belonging to bioprocess and bio-interfaces laboratory are cultivated in two media Bennett (rich) and GBA (minimum). Both media are tested in solid (agar) and liquid (broth) mode. The wettability θw, electron donor character ˠ (-), electron acceptor character ˠ (+) and Surface free energy ΔGiwi are determined using contact angle measurements. On the two solid media Bennett and GBA, Streptomyces strains develop a hydrophobic surface (96.9° <θw<167.9°) with a weak electron donor character (0.3 mJm-2 < (ˠ (-)) <12.14 mJm-2) and a strong electron acceptor character (0.26 mJm-2 < ˠ (+) < 17.8 mJm-2) and a negative surface free energy ((- 11.8 mJm-2) < ΔGiwi < (-110 mJm-2)). Whereas on both Bennett and GBA liquid media, the surfaces of Streptomyces strains are generally hydrophilic (1.3° < θw < 9.33°) with a strong electron donor character (13.76 mJm-2 < ( ˠ (-)) < 70.06 mJm-2) and a positive surface free energy. By changing the composition of the culture medium, only a slight change in the degree of hydrophobicity and surface free energy of Streptomyces is observed. Regarding the effect of medium composition on the surface properties of Streptomyces, the degree of wettability and the values of surface free energy are no longer the same when the composition of the medium changes. These results could be applied in further studies interested in interfacial phenomena and microbial adhesion in biotechnological fields.
Streptomyces has many advantages for exploration in biotechnological applications because of their ability to elaborate a multitude of bioactive molecules and secondary metabolites. Despite the importance of this genus in biotechnology, biofilm formation in Streptomyces is under-investigated. The objective of this research is to adapt two assays for the assessment of biofilm formation in Streptomyces. In the present investigation, we assess and follow biofilm formation in eight Streptomyces strains using quantitative and qualitative methods. The quantitative study based on a staining of the retained biomass in the microtiter plate with crystal violet “5%” and destaining using ethanol/acetone mixture, the concentration of crystal violet in the alcoholic solution reflect the intensity of the attached biofilm. On the other hand, the qualitative one consists of using modified freeman’s method a modified congo red agar method based on the color of colonies. Quantification of biomass by crystal violet staining method confirmed that Streptomyces bellus A43 and Streptomyces bellus A61 are biofilm-forming and this ability increase with the period of incubation. Our results showed that sixStreptomyces strains arenon-slime producing/non-biofilm forming. Two Streptomyces strains are slime producing/biofilm forming; this character vanishes at five days. Further research on genes responsible for biofilm formation in Streptomyces is highly recommended for better understanding of the phenomenon.
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