Streptomyces misionensis PESB-25 produces a thermoacidophilic endoglucanase using sugarcane bagasse and corn steep liquor as the sole organic substrates.

Streptomyces misionensis strain PESB-25 was screened and selected for its ability to secrete cellulases. Cells were grown in a liquid medium containing sugarcane bagasse (SCB) as carbon source and corn steep liquor (CSL) as nitrogen source, whose concentrations were optimized using response surface methodology (RSM). A peak of endoglucanase accumulation (1.01 U · mL(-1)) was observed in a medium with SCB 1.0% (w/v) and CSL 1.2% (w/v) within three days of cultivation. S. misionensis PESB-25 endoglucanase activity was thermoacidophilic with optimum pH and temperature range of 3.0 to 3.6 and 62° to 70 °C, respectively. In these conditions, values of 1.54 U mL(-1) of endoglucanase activity were observed. Moreover, Mn(2+) was demonstrated to have a hyperactivating effect on the enzyme. In the presence of MnSO4 (8 mM), the enzyme activity increased threefold, up to 4.34 U · mL(-1). Mn(2+) also improved endoglucanase stability as the catalyst retained almost full activity upon incubation at 50 °C for 4 h, while in the absence of Mn(2+), enzyme activity decreased by 50% in this same period. Three protein bands with endoglucanase activity and apparent molecular masses of 12, 48.5 and 119.5 kDa were detected by zymogram.

Streptomyces lunalinharesii strain 235 shows the potential to inhibit bacteria involved in biocorrosion processes.

Four actinomycete strains previously isolated from Brazilian soils were tested for their antimicrobial activity against Bacillus pumilus LF-4 and Desulfovibrio alaskensis NCIMB 13491, bacteria that are well known to be involved in biofilm formation and biocorrosion. Strain 235, belonging to the species Streptomyces lunalinharesii, inhibited the growth of both bacteria. The antimicrobial activity was seen over a wide range of pH, and after treatment with several chemicals and heat but not with proteinase K and trypsin. The antimicrobial substances present in the concentrated supernatant from growth media were partially characterized by SDS-PAGE and extracellular polypeptides were seen. Bands in the size range of 12 to 14.4 kDa caused antimicrobial activity. Transmission electron microscopy of D. alaskensis cells treated with the concentrated supernatant containing the antimicrobial substances revealed the formation of prominent bubbles, the spherical double-layered structures on the cell membrane, and the periplasmic space completely filled with electron-dense material. This is the first report on the production of antimicrobial substances by actinomycetes against bacteria involved in biocorrosion processes, and these findings may be of great relevance as an alternative source of biocides to those currently employed in the petroleum industry.