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In several Gram‐negative bacteria, the general stress response is mediated by the alternative sigma factor RpoS, a subunit of RNA polymerase that confers promoter specificity. In Escherichia coli, regulation of protein levels of RpoS involves the adaptor protein RssB, which binds RpoS for presenting it to the ClpXP protease for its degradation. However, in species from the Pseudomonadaceae family, RpoS is also degraded by ClpXP, but an adaptor has not been experimentally demonstrated. Here, we investigated the role of an E. coli RssB‐like protein in two representative Pseudomonadaceae species such as Azotobacter vinelandii and Pseudomonas aeruginosa. In these bacteria, inactivation of the rssB gene increased the levels and stability of RpoS during exponential growth. Downstream of rssB lies a gene that encodes a protein annotated as an anti‐sigma factor antagonist (rssC). However, inactivation of rssC in both A. vinelandii and P. aeruginosa also increased the RpoS protein levels, suggesting that RssB and RssC work together to control RpoS degradation. Furthermore, we identified an in vivo interaction between RssB and RpoS only in the presence of RssC using a bacterial three‐hybrid system. We propose that both RssB and RssC are necessary for the ClpXP‐dependent RpoS degradation during exponential growth in two species of the Pseudomonadaceae family. [ABSTRACT FROM AUTHOR]

Bacteria have a mechanism to rescue stalled ribosomes known as trans -translation consisting of SsrA, a transfer-messenger RNA (tmRNA), and the small protein SmpB. Other alternative rescue mechanisms mediated by ArfA and ArfB proteins are present only in some species. Ribosome rescue mechanisms also play a role in tolerance to antibiotics and various stresses such as heat. This study shows that the genome of the soil bacterium A. vinelandii harbours genes encoding for tmRNA, SmpB, two paralogs of ArfA (arfA1 and arfA2), and ArfB. A number of mutant strains carrying mutations in the ssrA, arfA1, arfA2 , and arfB genes were constructed and tested for their growth and susceptibility to heat and the antibiotic tetracycline. We found that the inactivation of both ssrA and one or the two arfA genes was detrimental to growth and caused a higher susceptibility to heat and to the antibiotic tetracycline. Interestingly, the arfB mutant strain was unable to grow after 2 h of incubation at 45°C. Inactivation of arfB in the ssrA-arfA1-arfA2 strain caused a lethal phenotype since the quadruple mutant could not be isolated. Taken together, our data suggest that both arfA1 and arfA2 , as well as arfB , are functional as back up mechanisms, and that the ArfB pathway has an essential role that confers A. vinelandii resistance to high temperatures. [ABSTRACT FROM AUTHOR]

Bursera microphylla A. Gray (Burseraceae) is a native plant of the Sonoran Desert, used in traditional medicine against different illnesses. The biological potential of B. microphylla has been associated with some groups of bioactive metabolites; amongst the most interesting for its biological effect are the lignan-type compounds. To date, the biological potential of fruits, leaves and stems of B. microphylla has not been widely explored; additionally, it is unknown if the seasons of the year modulate their biological activities and the profile of bioactive compounds. The objective of the present research was to determine the seasonality effect on the anti-inflammatory, antiproliferative potential and the lignan composition of B. microphylla. Ethanolic extracts of stems, leaves and fruits collected during spring, summer, autumn and winter (2019–2020) were obtained. The antiproliferative activity was evaluated against the cell lines C-33 A, HeLa, A549 and ARPE-19 by MTT assay. The anti-inflammatory effect was determined in RAW 264.7-activated with LPS through the quantification of nitric oxide (NO) using the Griess method. The profile of bioactive compounds was investigated by ESI-IT-MSn analysis. Fruits extracts exhibited the highest potential to inhibit the NO production, followed by the stems and leaves extracts. In the same way, fruits extracts displayed the highest antiproliferative activity followed by the stems and leaves extracts. C-33 A was the most sensitive to the treatments, followed by HeLa, A549 and ARPE-19. The chemical analysis allowed the identification of 5 new lignan-type compounds in the extract (hinokinin, 3,4-dimethoxy-3′,4′-methylenedioxylignano-9,9′-epoxylignan- 9′-ol, 7′,8′-dehydropodophyllotoxin, β-peltatin A-methyl ether and 7′, 8′-dehydroacetylpodophyllotoxin). The results show that seasonality modulates the anti-inflammatory, the antiproliferative potential, and the chemical composition of the extracts. The above suggests that B. microphylla could represent a potential source of phytochemicals for the development of pharmacological therapies for inflammation and cancer. • Spring (leaves and stems) and summer fruits extracts showed the highest capability to inhibit the NO production. • Spring (leaves and stems) and summer fruits showed the most potential to reduce the proliferation of cancer cells. • Eleven lignans were found in the extracts, five of them were described for the first time in B. microphylla. • Seasonality modulate the anti-inflammatory, antiproliferative potential and the lignan composition of B. microphylla. [ABSTRACT FROM AUTHOR]