Diversity and Antimicrobial Properties of Actinomycetes Associated with Some Edible Freshwater Macroalgae

Abstract

In this study, actinomycetes associated with Nostoc commune and Nostochopsis spp. were investigated. Actinomycetes were isolated through the use oftwelve different types of media. In terms of overall isolation, a total of 80 isolates of actinomycetes were obtained. Fifty isolates were obtained from Nostoc commune. SCA+algae extract produced the highest number of isolates at 10. On the other hand, thirty isolates were obtained from Nostochopsis spp., for which the HTA medium gave the highest number of isolates at 7. The effects of the isolation media were recorded. The highest numbers of actinomycetes associated with N. communewas found in the starch casein agar (SC)(2.5x104+5.2 CFU.g-1). Whereas, the Minimal medium with extracts (MM+Nt) revealed the highest number of isolates of actinomycetes that were associated with Nostochopsis spp. (2.25x104 CFU.g-1). The morphology of all the isolates on ISP1, ISP2 and ISP6 medium were used for the purposes of classification. Two groups (streptomycetes and non- streptomycetes) and 2 subgroups (filamentous actinomycetes and non - filamentous actinomycetes) were found. In addition, Streptomyces was found to be the majority genus. The results of morphological observations and the molecular study were congruent. The diversity of the independent culture of actinobacteria associated with Nostoc commune Voucher Bornet&Flahault was assessed by the cloning and sequencing of the actinobacterial-derived partial 16S rRNA gene. In total, 70 clones were obtained. The phylogenetic tree of all clone sequences was congruent with the BLAST result.The majority of the clones were found to be actinobacteria. Microbacterium and Pseudonocardia were considered the most diverse genera. However, there were 5 clones that revealed very few similarities with any known actinobacterial sequences and formed a separate cluster. This was pobably because our results suggested that some of the Nostoc commune associated actinobacteria are considered novel at the genus and species level. Moreover, the rarefaction curve clearly did not reach the saturation point which indicated that greater sampling of the clone library probably resulted inan additional level of diversity. The Shannon-Wiener and Chao1 indexes was also investigated. The evenness of the clone library was considering high. In addition, the coverage value was 71.11% indicating that this library did not cover all of the diversity presented in the samples. Nevertheless, the diversity of the clone library obtained in the present study was considered more diverse than those previously reported. From a study of the antimicrobial activities, actinomycetes isolated from Nostoc commune, which were cultured in M30, showed an inhibitory effect against Methicillin-resistant Staphylococcus aureus. In M52 medium, Escherichia coli O157 was inhibited by 21 isolates. On the other hand, the isolates from Nostochopsis spp., yielded 20 isolated which were incubated in Med.30, while 18 isolates that were cultured in M52 revealed the inhibitory effects against Aeromonas hydrophila. Moreover, NCMn07 and NTRHn08 showed significant activities against all 7 pathogens. These 2 strains were identified by comparing with the data in Eztaxone using 16S rDNA sequence and these indicated that NCMn07 produced 81% in terms of similarities to Streptomyces atrovirensNRRL B-16357(T), while isolate NTRHn08 revealed 97% in similarities to Streptomyces griseoflavusLMG 19344(T).