Aims: Detection and identification of new antagonistic activities towards Bacillus cereus and relatives. Methods and Results: Twenty Bacillus thuringiensis strains were screened for their capacity to express bacteriocin‐like agents. Strain BMG1.7, isolated from soil, showed an antagonistic activity called thuricin 7. Thuricin 7 was active against several species of the genus Bacillus, including three of the four known B. thuringiensis/B. cereus bacteriocin producers, as well as against Streptococcus pyogenes and Listeria monocytogenes strains. Antimicrobial activity was lost after treatment with proteinase K. The active protein had an apparent molecular weight of 11·6 kDa, and was secreted at the end of the exponential growth phase. Thuricin 7 retained 55% of the activity after incubation at 98°C for 30 min. The mode of action of thuricin 7 was shown to be bactericidal and bacteriolytic. Conclusions: Thuricin 7 is a novel bacteriocin produced by a newly isolated Bacillus thuringiensis strain BMG1.7. Significance and Impact of the Study: The characteristics of thuricin 7 indicate that it is a new bacteriocin which may have interesting biotechnological applications due to its relatively large activity spectrum.

Summary Oases are desert‐farming agro‐ecosystems, where date palm (Phoenix dactylifera L.) plays a keystone role in offsetting the effects of drought and maintaining a suitable microclimate for agriculture. At present, abundance, diversity and plant growth promotion (PGP) of date palm root‐associated bacteria remain unknown. Considering the environmental pressure determined by the water scarcity in the desert environments, we hypothesized that bacteria associated with date palm roots improve plant resistance to drought. Here, the ecology of date palm root endophytes from oases in the Tunisian Sahara was studied with emphasis on their capacity to promote growth under drought. Endophytic communities segregated along a north–south gradient in correlation with geo‐climatic parameters. Screening of 120 endophytes indicated that date palm roots select for bacteria with multiple PGP traits. Bacteria rapidly cross‐colonized the root tissues of different species of plants, including the original Tunisian date palm cultivar, Saudi Arabian cultivars and Arabidopsis. Selected endophytes significantly increased the biomass of date palms exposed to repeated drought stress periods during a 9‐month greenhouse experiment. Overall, results indicate that date palm roots shape endophytic communities that are capable to promote plant growth under drought conditions, thereby contributing an essential ecological service to the entire oasis ecosystem.

17Background Aridification is a worldwide serious threat directly affecting agriculture and crop production. In arid

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Mung bean nuclease treatment of 16S-23S ribosomal DNA intergenic transcribed spacers (ITS) amplified (45) and is widely used for the biological control of insects in crop protection; B. mycoides has been recognized as a plant growth-promoting bacterium associated with conifer roots (38); B. weihenstephanensis, a psychrotolerant species frequently found in pasteurized milk, is a potential cause of spoilage problems (32). The six species are not easily distinguished on the basis of phenotypic or genetic traits (48). Recently, B. anthracis, B. cereus, and B. thuringiensis were found to be very closely related, and it has been proposed that they belong to a single species (24,33). This proposal has been based on multilocus enzyme electrophoresis data and sequencing of discrete genetic loci (24) and on the presence of an S-layer on the cell surface (33). The model considering B. anthracis, B. cereus, and B. thuringiensis as subspecies of a phylogenetically monomorphic group, differing mainly in characters linked to mobile genetic elements such as plasmids, is supported by very high sequence homology in the conserved molecular chronometers of the ribosomal operons, the 16S and 23S ribosomal DNA (rDNA), and the short intergenic spacer between them (3-5, 7, 21, 30). Considering the dangerousness of B. anthracis and the wide in-field application of B. thuringiensis as a biological insecticide, it would be opportune to further evaluate the phylogenetic relationship between the different clades of the B. cereus group. Whole-genome sequencebased analysis could give a definitive view of the genetic relationship between these species (29). However, an approach that is economically feasible, given current technology, is possible for few strains in a given species (42). Hence, for phylogenetic surveys based on a relatively large number of isolates of each species, permitting an assessment of the amount of variability and overlap within a species, the best means of approach remains the use of highly conserved molecules with no, or a low, horizontal gene transfer rate such as the ribosomal operon.In the prokaryote genome, the ribosomal operon can be present in multiple copies, up to 15 copies in Clostridium paradoxum (41). The 16S-23S rDNA intergenic transcribed spacers (ITS) are the most variable regions of the ribosomal operon, and, apart from interoperonic nucleotide substitutions, insertions, and deletions, such ITS can be differentiated, given the presence of the different numbers and types of tRNA genes (9,10,31,49). Since the ITS have fewer functional constraints than the adjacent ribosomal genes, which undergo concerted evolution (17-19), their sequences can contain traces of ribosomal operon rearrangements and species-specific or even strain-specific traits that are useful for strain typing.An analysis of ITS homoduplex-heteroduplex polymorphisms has shown that wide variability exists in the strains of the six species of the B. cereus group (14), indicating widely different length and sequence polymorphisms among the 8 t...

A total of 119 lactic acid bacteria (LAB) were isolated, by culture-dependant method, from rhizosphere samples of olive trees and desert truffles and evaluated for different biotechnological properties. Using the variability of the intergenic spacer 16S-23S and 16S rRNA gene sequences, the isolates were identified as the genera Lactococcus, Pediococcus, Lactobacillus, Weissella, and Enterococcus. All the strains showed proteolytic activity with variable rates 42% were EPS producers, while only 10% showed the ability to grow in 9% NaCl. In addition, a low rate of antibiotic resistance was detected among rhizospheric enterococci. Furthermore, a strong antibacterial activity against plant and/or pathogenic bacteria of Stenotrophomonas maltophilia, Pantoea agglomerans, Pseudomonas savastanoi, the food-borne Staphylococcus aureus, and Listeria monocytogenes was recorded. Antifungal activity evaluation showed that Botrytis cinerea was the most inhibited fungus followed by Penicillium expansum, Verticillium dahliae, and Aspergillus niger. Most of the active strains belonged to the genera Enterococcus and Weissella. This study led to suggest that environmental-derived LAB strains could be selected for technological application to control pathogenic bacteria and to protect food safety from postharvest deleterious microbiota.

The association between plant and plant growth promoting bacteria (PGPB) contributes to the successful thriving of plants in extreme environments featured by water shortage. We have recently shown that, with respect to the non-cultivated desert soil, the rhizosphere of pepper plants cultivated under desert farming hosts PGPB communities that are endowed with a large portfolio of PGP traits. Pepper plants exposed to bacterial isolates from plants cultivated under desert farming exhibited a higher tolerance to water shortage, compared with untreated control. This promotion was mediated by a larger root system (up to 40%), stimulated by the bacteria, that enhanced plant ability to uptake water from dry soil. We provide initial evidence that the nature of the interaction can have a limited level of specificity and that PGPB isolates may determine resistance to water stress in plants others than the one of the original isolation. It is apparent that, in relation to plant resistance to water stress, a feature of primary evolutionary importance for all plants, a cross-compatibility between PGPB and different plant models exists at least on a short-term.

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