Morphological, physiological and plant infectivity characterization of Frankia strains isolated from Casuarina’s nodules

Abstract

Frankia are soil microorganisms that form symbiosis with roots of tree species called actinorhizal plants and are capable of fixing atmospheric N2. This study was carried out to characterize morphologically, physiologically and to assess the nodulation of four Frankia reference strains (HFPCcI3, JCT287, KB5 and F59) and 12 (IPRF) isolated from root nodules of Casuarina plants. All strains (Reference and IPRF) were characterized as Gram-positive and 50% as acid-fast. The Frankia strains produced alkali in the culture medium, except the IPRF006, IPRF008 and IPRF010. The colonies of strains F59, IPRF002, IPRF004, IPRF005, and IPRF011 produced melanin. Among reference strains, only JCT287 grew in culture media with pH 5.5, while with pH 6.0 both strains JCT287 and KB5 presented growth. The regression analysis showed a linear relationship (Y = 67.56+ 3.88X and R2=0.5862, p < 0.05) and Pearson’s correlation coefficient (r=0.766, p < 0.05) between number of spores and hyphae (120 to 480 UFC mL-1) and total protein (18 to 145 µg mL-1). It was observed that the strains F59 had a higher proportion of total protein 50.0% than JCT287 with 7.0% and that the IPRF strains showed values between 17.5 and 29.3%. All strains presented ability to produce indolic compounds in growth media with values ranging from 5.9 to 98.8 µM.