Candida glabrata is the second most common cause of candidemia, and its ability to adhere to different host cell types, to microorganisms, and to medical devices are important virulence factors. Here, we consider three characteristics that confer extraordinary advantages to C. glabrata within the host. (1) C. glabrata has a large number of genes encoding for adhesins most of which are localized at subtelomeric regions. The number and sequence of these genes varies substantially depending on the strain, indicating that C. glabrata can tolerate high genomic plasticity; (2) The largest family of CWPs (cell wall proteins) is the EPA (epithelial adhesin) family of adhesins. Epa1 is the major adhesin and mediates adherence to epithelial, endothelial and immune cells. Several layers of regulation like subtelomeric silencing, cis-acting regulatory regions, activators, nutritional signaling, and stress conditions tightly regulate the expression of many adhesin-encoding genes in C. glabrata, while many others are not expressed. Importantly, there is a connection between acquired resistance to xenobiotics and increased adherence; (3) Other subfamilies of adhesins mediate adherence to Candida albicans, allowing C. glabrata to efficiently invade the oral epithelium and form robust biofilms. It is noteworthy that every C. glabrata strain analyzed presents a unique pattern of CWPs at the cell surface.

Among sequenced genomes, it is common to find a high proportion of genes encoding proteins that cannot be assigned a known function. In bacterial genomes, genes related to a similar function are often located in contiguous regions. The presence of genes encoding conserved hypothetical proteins (chp) in such a region may suggest that they are related to that particular function. Plasmid pRet42a from Rhizobium etli CFN42 is a conjugative plasmid containing a segment of approximately 30 Kb encoding genes involved in conjugative transfer. In addition to genes responsible for Dtr (DNA transfer and replication), Mpf (Mating pair formation) and regulation, it has two chp-encoding genes (RHE_PA00163 and RHE_PA00164) and a transcriptional regulator (RHE_PA00165). RHE_PA00163 encodes an uncharacterized protein conserved in bacteria that presents a COG4634 conserved domain, and RHE_PA00164 encodes an uncharacterized conserved protein with a DUF433 domain of unknown function. RHE_PA00165 presents a HTH_XRE domain, characteristic of DNA-binding proteins belonging to the xenobiotic response element family of transcriptional regulators. Interestingly, genes similar to these are also present in transfer regions of plasmids from other bacteria. To determine if these genes participate in conjugative transfer, we mutagenized them and analyzed their conjugative phenotype. A mutant in RHE_PA00163 showed a slight (10 times) but reproducible increase in transfer frequency from Rhizobium donors, while mutants in RHE_PA00164 and RHE_PA00165 lost their ability to transfer the plasmid from some Agrobacterium donors. Our results indicate that the chp-encoding genes located among conjugation genes are indeed related to this function. However, the participation of RHE_PA00164 and RHE_PA00165 is only revealed under very specific circumstances, and is not perceived when the plasmid is transferred from the original host. RHE_PA00163 seems to be a fine-tuning modulator for conjugative transfer.

Candida glabrata is a fungal pathogen frequently found as a commensal in humans. To colonize and disseminate successfully in the mammalian host, C. glabrata must detect signals within the host and reprogram gene expression to respond appropriately to hostile environmental conditions. One of the layers of regulation of expression of many virulence-related genes (adhesin-encoding genes, genes involved in response to oxidative stress and xenobiotics) is achieved through epigenetic mechanisms. Local and regional silencing is mediated by the activity of two NAD(+)-dependent histone deacetylases, Hst1 and Sir2, respectively, repressing many virulence genes. Hst1 and Sir2 interact with different repressor complexes to achieve regional or local silencing. Sir2 can associate with Sir4, which is then recruited to the telomere by Rap1 and yKu. Deacetylation of the histone tails creates high affinity binding sites for new molecules of the Sir complex, thereby spreading the silent domain over >20 kb. Many of the adhesin-encoding EPA genes are subject to this regulation. Hst1 in turn associates with the Sum1-Rfm1 complex. Sum1 is a DNA-binding protein, which recognizes specific sites at individual promoters, recruiting Hst1 to specific genes involved in the response to oxidative stress and xenobiotics, which results in their repression.

Hypericum silenoides Juss. 1804 is an important medicinal plant used in Mexico, but the bacterial community associated with it is unknown. The bacterial communities in the rhizosphere and roots of H. silenoides were isolated and identified by enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR) and ribosomal types were determined by amplified ribosomal rDNA restriction analysis (ARDRA) and 16S rRNA gene sequences. Sixty-six strains were obtained from roots of H. silenoides and 37 were isolated from the rhizosphere. ERIC fingerprinting distinguished 63 genetic patterns with 44 being unique and the remaining 19 containing 59 strains. Eighteen representative strains were distinguished with ARDRA analysis. 16S rRNA gene sequence analysis revealed that the bacteria isolated from the roots and rhizosphere of H. silenoides belonged to the genera Acinetobacter, Enterobacter, Pseudomonas, Sphingobium, Stenotrophomonas, Agrobacterium, Pantoea and Serratia. The largest number of isolates (30) belonged to the genus Agrobacterium. Richness and diversity of bacteria was higher on the roots than in the rhizosphere of H. silenoides.

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