RESUMO

Citrus canker is one of the main bacterial diseases that affect citrus crops and is caused by Xanthomonas citri which affects all citrus species worldwide. New strategies to control citrus canker are necessary and the use of bacteriophages as biocontrol agent could be an alternative. Phages that infect Xanthomonas species have been studied, such as XacN1, a myovirus that infects X. citri. Here we report the isolation and characterization of a new jumbo phage, vb_XciM_LucasX, which infects X. citri and X. fuscans. Transmission electron microscopy allowed classification of LucasX in the Myoviridae family, which was corroborated by its genomic sequencing, annotation, and proteome clustering. LucasX has a 305,651 bp-long dsDNA genome. ORF prediction and annotation revealed 157 genes encoding putative structural proteins such as capsid and tail related proteins and phage assembly associated proteins, however, for most of the structural proteins it was not possible assign specific functions. Its genome encodes several proteins related to DNA replication and nucleotide metabolism, five putative RNA polymerases, at least one homing endonuclease mobile element, a terminase large subunit (TerL), an endolysin and many proteins classified as beneficial to the host. Proteome clustering and phylogeny analyses showed that LucasX is a new jumbo phage having as its closest neighbor the Xanthomonas jumbo phage Xoo-sp14. LucasX presented a burst size of 40 PFU/infected cell of X. citri 306, was completely inactivated at temperatures above 50°C, presented survival lower than 25% after 80 s of exposition to artificial UV light and had practically no tolerance to concentrations above 2.5 g/L NaCl or 40% ethanol. LucasX presented optimum pH at 7 and a broad range of Xanthomonas hosts, infecting twenty-one of the twenty-three strains tested. Finally, the LucasX yield was dependent on the host strain utilized, resulting one order of magnitude higher in X. fuscans C 752 than in X. citri 306, which points out to the possibility of phage yield improvement, an usual challenge for biocontrol purposes.

Assuntos

RESUMO

All Triportheus species show the conserved diploid number of 52 chromosomes and a ZZ/ZW sex chromosome system. Previous studies conducted on Triportheus nematurus reported a syntenical location of 18S and 5S sites on this species, in addition to some indications that this condition could be shared by other Triportheus species, possibly constituting a synapomorphy for this genus. In the present study, fluorescence in situ hybridization (FISH) experiments were performed in seven Triportheus species in view of a comparative analysis of the distribution of the 18S and 5S ribosomal DNAs on the chromosomes. The double-FISH experiments have showed that the synteny of the 18S and 5S rDNA genes is not a synapomorphy for the genus, since it is not present in all the species investigated, although it is present in most of them. The findings suggest that the syntenical location of the ribosomal genes is an ancestral trait in Triportheus, which was changed during the course of evolution of this group.

Assuntos

RESUMO

Despite substantial progress, there are still several gaps in our knowledge about the process of sex chromosome differentiation. The degeneration of sex-specific chromosome in some species is well documented, but it is not clear if all species follow the same evolutionary pathway. The accumulation of repetitive DNA sequences, however, is a common feature. To better understand this involvement, fish species emerge as excellent models because they exhibit a wide variety of sex chromosome and sex determining systems. Besides, they have much younger sex chromosomes compared to higher vertebrates, making it possible to follow early steps of differentiation. Here, we analyzed the arrangement of 9 repetitive DNA sequences in the W chromosomes of 2 fish species, namely Leporinus reinhardti and Triportheus auritus, which present well-differentiated ZZ/ZW sex system, but differ in respect to the size of the sex-specific chromosome. Both W chromosomes are almost fully heterochromatic, with accumulation of repeated DNAs in their heterochromatic regions. We found that microsatellites have strongly accumulated on the large W chromosome of L. reinhardti but not on the reduced-size W chromosome of T. auritus and are therefore important players of the W chromosome expansion. The present data highlight that the evolution of the sex chromosomes can diverge even in the same type of sex system, with and without the degeneration of the specific-sex chromosome, being more dynamic than traditionally appreciated.