To cheat or not to cheat: cheatable and non-cheatable virulence factors in Pseudomonas aeruginosa.

Important bacterial pathogens such as Pseudomonas aeruginosa produce several exoproducts such as siderophores, degradative enzymes, biosurfactants, and exopolysaccharides that are used extracellularly, benefiting all members of the population, hence being public goods. Since the production of public goods is a cooperative trait, it is in principle susceptible to cheating by individuals in the population who do not invest in their production, but use their benefits, hence increasing their fitness at the expense of the cooperators' fitness. Among the most studied virulence factors susceptible to cheating are siderophores and exoproteases, with several studies in vitro and some in animal infection models. In addition to these two well-known examples, cheating with other virulence factors such as exopolysaccharides, biosurfactants, eDNA production, secretion systems, and biofilm formation has also been studied. In this review, we discuss the evidence of the susceptibility of each of those virulence factors to cheating, as well as the mechanisms that counteract this behavior and the possible consequences for bacterial virulence.

Parasitemia and Differential Tissue Tropism in Mice Infected with Trypanosoma cruzi Isolates Obtained from Meccus phyllosoma in the State of Oaxaca, Mexico.

Trypanosoma cruzi is a parasite transmitted by the feces of triatomines. Many triatomine species are found in Mexico, and various T. cruzi variants have been isolated from these species, each showing very different virulence and cell tropism. The isolates were obtained from Meccus phyllosoma specimens in three localities in the state of Oaxaca, Mexico: Tehuantitla, Vixhana, and Guichivere. The virulence of each isolate was assessed by quantifying parasitemia, survival, and histopathologic findings. The lineage of each isolate was identified using the mini-exon gene. The expression of the tssa gene during infection was detected in the heart, esophagus, gastrocnemius, and brain. Our results show that the maximum post-infection parasitemia was higher for the Tehuantitla isolate. On genotyping, all isolates were identified as T. cruzi I. The amastigotes in the heart and gastrocnemius were verified for all isolates, but in the brain only for Tehuantitla and Vixhana. The tssa expression allowed us to detect T. cruzi isolates, for Tehuantitla, predominantly in the heart. For Vixhana, a higher tssa expression was detected in gastrocnemius, and for Guichivere, it was higher in the esophagus. Results show that virulence, tropism, and tssa expression can vary, even when the isolates are derived from the same vector species, in the same region, and at similar altitudes.

Microbiota from Rhabditis regina may alter nematode entomopathogenicity.

Here we report the presence of the entomopathogenic nematode Rhabditis (Rhabditoides) regina affecting white grubs (Phyllophaga sp. and Anomala sp.) in Mexico and R. regina-associated bacteria. Bioassays were performed to test the entomopathogenic capacity of dauer and L2 and L3 (combined) larval stages. Furthermore, we determined the diversity of bacteria from laboratory nematodes cultivated for 2 years (dauer and L2-L3 larvae) and from field nematodes (dauer and L2-L3 larvae) in addition to the virulence in Galleria mellonella larvae of some bacterial species from both laboratory and field nematodes. Dauer and non-dauer larvae of R. regina killed G. mellonella. Bacteria such as Serratia sp. (isolated from field nematodes) and Klebsiella sp. (isolated from larvae of laboratory and field nematodes) may explain R. regina entomopathogenic capabilities. Different bacteria were found in nematodes after subculturing in the laboratory suggesting that R. regina may acquire bacteria in different environments. However, there were some consistently found bacteria from laboratory and field nematodes such as Pseudochrobactrum sp., Comamonas sp., Alcaligenes sp., Klebsiella sp., Acinetobacter sp., and Leucobacter sp. that may constitute the nematode microbiome. Results showed that some bacteria contributing to entomopathogenicity may be lost in the laboratory representing a disadvantage when nematodes are cultivated to be used for biological control.

Sexual dimorphism in immune response: testing the hypothesis in an insect species with two male morphs.

It has been proposed that given that males should invest in sexual traits at the expense of their investment in immune response, females are better immunocompetent than males. Typically, this idea has been tested in monomorphic species, but rarely has been evaluated in polymorphic male species. We used Paraphlebia zoe, a damselfly with two male morphs: the black-winged morph (Black-W) develop black spots as sexual traits and the hyaline-winged morph (Hyaline-W) resembles a female in size and wings color. We predicted that Black-W should have a lower immune response than Hyaline-W, but that the latter males should not differ from females in this respect. Nitric oxide (NO) and phenoloxidase (PO) production, as well as hemolymph protein content, were used as immune markers. Body size (wing length) was used as an indicator of the male condition. The results show that, as we predicted, females and Hyaline-W had higher values of NO than Black-W, corresponding to differences in size. However, the opposite was found in relation to PO production. Females had the highest levels of hemolymph protein content, whereas no differences were found between Black-W and Hyaline-W. These results partially support the sexual selection hypothesis and are discussed in the context of the life history of this species. Black-W, Hyaline-W, and females could express the immune markers that are prioritized by their particular condition, and probably neither of them could express all immune markers in an elevated manner, as this would result in an excessive accumulation of free radicals.