The molecular marker-based comparison of Azotobacter spp. populations isolated from industrial soils of Cracow-Nowa Huta steelworks (southern Poland) and the adjacent agricultural soils

Preparation of bacterial fertilizer from biogas residue after anaerobic co-digestion of kitchen waste and residual sludge

Azotobacter chroococcum and Bacillus subtilis were selected as fermentation strains, and biogas residue after anaerobic digestion of kitchen waste and residual sludge was used as fermentation substrate. A single factor optimization test was used to optimize the solid-state fermentation parameters of biogas residue with the number of viable bacteria and the number of spores as indexes. The results showed that the optimum inoculation conditions involved the following: 55% initial moisture content, 15% initial inoculation amount, 30 ℃, and 1:1 initial inoculation ratio for 13 days. Pot experiment showed that the prepared three kinds of bacterial fertilizers could not only effectively promote the growth of white clover, improve the composition of soil nutrients, but also change the structure of soil bacterial community, which is of great significance to the health of soil ecosystem in white clover.

Identification and molecular characterization of Azotobacter chroococcum and Azotobacter salinestris using ARDRA, REP, ERIC, and BOX

Azotobacter chroococcum and A. salinestris do not possess significant and distinct morphological and physiological differences and are often mistaken with each other in microbiological research. In this study, 12 isolates of Azotobacter isolated by standard protocol from soils were identified morphologically and physiologically as A. chroococcum. The isolates were more closely investigated for the molecular differentiation and diversity of A. chroococcum and A. salinestris. For this purpose, the ARDRA technique including HpaII, RsaI, and AluI restriction enzymes, and REP, ERIC, and BOX markers were used. The nifD and nifH genes were also utilized to evaluate the molecular identification of these two species. The 16S rDNA evaluation showed that only four out of the 12 isolates were identified as A. chroococcum and the rest were A. salinestris. The results revealed that HpaII was able to differentiate A. chroococcum from A. salinestris whereas RsaI and AluI were not able to separate them. Moreover, BOX and REP markers were able to differentiate between A. chroococcum and A. salinestris. However, ERIC marker and nifD and nifH genes were unable to separate these species. According to the results, HpaII restriction enzyme is suggested to save time and cost. BOX and REP markers are recommended for differentiation and clear discrimination not only between A. chroococcum and A. salinestris but also among their strains.

Taxonomy and systematics of plant probiotic bacteria in the genomic era

Recent decades have predicted significant changes within our concept of plant endophytes, from only a small number specific microorganisms being able to colonize plant tissues, to whole communities that live and interact with their hosts and each other. Many of these microorganisms are responsible for health status of the plant, and have become known in recent years as plant probiotics. Contrary to human probiotics, they belong to many different phyla and have usually had each genus analysed independently, which has resulted in lack of a complete taxonomic analysis as a group. This review scrutinizes the plant probiotic concept, and the taxonomic status of plant probiotic bacteria, based on both traditional and more recent approaches. Phylogenomic studies and genes with implications in plant-beneficial effects are discussed. This report covers some representative probiotic bacteria of the phylum Proteobacteria, Actinobacteria, Firmicutes and Bacteroidetes, but also includes minor representatives and less studied groups within these phyla which have been identified as plant probiotics.