Phenotype of the Escherichia coli Culture Immobilized in Silanol Humate Gel

Abstract— Immobilization of members of various bacterial species, including Escherichia coli, into silanol-humate gels (SHG) results in a 10–1000 higher number of cells surviving long-term storage at room conditions. We suggested the surviving cells to possess the properties of the cells developing in biofilms (BF), the biofilm phenotype (BFP). The goal of the work was to confirm or refute the suggestion on occurrence of the cells exhibiting the BF phenotype according to their physiological, cytomorphological, and genetic characteristics in SHG-immobilized E. coli populations. The BFP cytomorphological markers were cell aggregation and extracellular specific formations (projections, cell wall protrusions termed protoprosthecae). Both in BF and SHG, some cells (15–30% of the population) possessed projections 0.25–1 cell length long. In the stationary culture, similar formations, albeit of smaller size (up to 0.25 cell length) were found only in 2–3% of the cells. The physiological parameter (specific respiratory rate) of BF and SHG-immobilized E. coli was lower than in the growing culture, but higher than in the stationary-stage culture. Real-time quantitative PCR with reverse transcriptase (Q-RT-PCR) revealed that activity of the BFP marker genes (cellulose synthase, bcsA; regulator of BFP transition, csgD; synthesis of the adhesine poly-(β-1,6-N-acetyl-D-glucosamine), pgaC; and antigen 43, inducing cell aggregation, flu), was 1.3–5 times higher in both SHG-immobilized and biofilm E. coli cells than in the cells of stationary-phase culture. Thus, E. coli cells developing in SHG were in the state with some BFP characteristics, although with significant differences from it. This makes it possible to speak of a new, previously unknown E. coli phenotype occurring in the cells immobilized in a gel environment.