Bacteria present in natural environments such as soil have evolved multiple strategies to escape predation. We report that natural isolates of Enterobacteriaceae that actively hydrolyze plant-derived aromatic b-glucosides such as salicin, arbutin and esculin, are able to avoid predation by the bacteriovorous amoeba Dictyostelium discoideum and nematodes of multiple genera belonging to the family Rhabditidae. This advantage can be observed under laboratory culture conditions as well as in the soil environment. The aglycone moiety released by the hydrolysis of b-glucosides is toxic to predators and acts via the dopaminergic receptor Dop-1 in the case of Caenorhabditis elegans. While soil isolates of nematodes belonging to the family Rhabditidae are repelled by the aglycone, laboratory strains and natural isolates of Caenorhabditis sp. are attracted to the compound, mediated by receptors that are independent of Dop-1, leading to their death. The b-glucosides-positive (Bgl þ ) bacteria that are otherwise non-pathogenic can obtain additional nutrients from the dead predators, thereby switching their role from prey to predator. This study also offers an evolutionary explanation for the retention by bacteria of 'cryptic' or 'silent' genetic systems such as the bgl operon.

Utilization of the aryl-β-glucosides salicin or arbutin in most wild-type strains of E. coli is achieved by a single-step mutational activation of the bgl operon. Shigella sonnei, a branch of the diverse E. coli strain tree, requires two sequential mutational steps for achieving salicin utilization as the bglB gene, encoding the phospho-β-glucosidase B, harbors an inactivating insertion. We show that in a natural isolate of S. sonnei, transcriptional activation of the gene SSO1595, encoding a phospho-β-glucosidase, enables salicin utilization with the permease function being provided by the activated bgl operon. SSO1595 is absent in most commensal strains of E. coli, but is present in extra-intestinal pathogens as bgcA, a component of the bgc operon that enables β-glucoside utilization at low temperature. Salicin utilization in an E. coli bglB laboratory strain also requires a two-step activation process leading to expression of BglF, the PTS-associated permease encoded by the bgl operon and AscB, the phospho-β-glucosidase B encoded by the silent asc operon. BglF function is needed since AscF is unable to transport β-glucosides as it lacks the IIA domain involved in phopho-relay. Activation of the asc operon in the Sal(+) mutant is by a promoter-up mutation and the activated operon is subject to induction. The pathway to achieve salicin utilization is therefore diverse in these two evolutionarily related organisms; however, both show cooperation between two silent genetic systems to achieve a new metabolic capability under selection.

Rich resource Mycelium dense and compact for resource exploitation Poor resource Mycelium thin for resource exploration B: Resource durability Short-lived resources (e.g., dung or rotting fruit) Fast mycelial growth for resource capture and then one-time reproduction after resource capture ("bang-bang life-history")semelparous life style Long-lived resources (e.g., dead tree) Slower growth and late reproduction start, with multiple reproductive periods -iteroparous life style C: Presence of competition No interaction between individuals Grow fast to monopolize resources Metabolic interactions between individuals Engage in cross-feeding or interference competition D: Conditions causing positive, negative or no MGR-spore yield correlation Novel condition causing low fitness No tradeoff, growth rate and reproduction may be positively correlated and both may improve adaptively Condition to which the fungus is relatively well adapted Tradeoff between growth rate and reproduction may be apparent and constrain further adaptation Table 1.1: Overview of the various life-history options that a fungus may adopt based on environmental conditions. (A) Resource quality, (B) Resource durability, (C) Presence of multiple individuals. (D) Describes general conditions for a tradeoff between mycelial growth rate and asexual spore yield. The alternate strategies mentioned in (A-C) are not necessarily mutually exclusive and most fungi are likely to employ a combination of these strategies based on ecology and organismal biology.

In the trishanku (triA-) mutant of the social amoeba Dictyostelium discoideum, aggregates are smaller than usual and the spore mass is located mid-way up the stalk, not at the apex. We have monitored aggregate territory size, spore allocation and fruiting body morphology in chimaeric groups of (quasi-wild-type) Ax2 and triA- cells. Developmental canalisation breaks down in chimaeras and leads to an increase in phenotypic variation. A minority of triA- cells causes largely Ax2 aggregation streams to break up; the effect is not due to the counting factor. Most chimaeric fruiting bodies resemble those of Ax2 or triA-. Others are double-deckers with a single stalk and two spore masses, one each at the terminus and midway along the stalk. The relative number of spores belonging to the two genotypes depends both on the mixing ratio and on the fruiting body morphology. In double-deckers formed from 1:1 chimaeras, the upper spore mass has more Ax2 spores, and the lower spore mass more triA- spores, than expected. Thus, the traits under study depend partly on the cells' own genotype and partly on the phenotypes, and so genotypes, of other cells: they are both autonomous and non-autonomous. These findings strengthen the parallels between multicellular development and behaviour in social groups. Besides that, they reinforce the point that a trait can be associated with a genotype only in a specified context.

S6.3 Fungal adaptation and evolution, September 22, 2022, 4:45 PM - 6:15 PM A total of 12 replicate populations initiated with a laboratory strain of the ascomycete fungus Aspergillus nidulans evolved on synthetic minimal glucose agar medium for 1 year, using weekly transfers of 1% of the produced asexual spores to fresh medium. This Aspergillus short-term evolution experiment (ASEX) was designed to understand how filamentous fungi adapt to growth on limited carbon in a spatially structured environment. We observed no systematic improvement in the fitness components tested and neither in the competitive fitness relative to the ancestor. Instead, we observed the repeated evolution of at least two morphotypes, with a fluffy-like (FL) or an ancestor-like (AL) colony morphology, leading to non-transitive fitness interactions among isolates in two selected populations. The genomic analyses of clones from all 12 populations at an early (week 10) and the final time point (week 52), show a clear role of natural selection during ASEX. We also observed a shared genetic basis and different timing of adaptation of AL and FL types. In addition, in most populations, both morphotypes do not form monophyletic groups, but they frequently disappear and re-evolve from ancestral forms of both types. Reduction in asexual spore yield, the most evident parallel phenotypic change found in all our evolved populations, is not due to the direct selection of genes involved in asexual reproduction. Instead, we argue that reduced spore yield is a pleiotropic effect of adaptive changes in metabolism.