Influence of Intracellular Nitrogen Status and Dynamic Control of Central Metabolism in the Plant Symbiont Sinorhizobium meliloti

Sinorhizobium meliloti is a soil bacterium capable of forming an intracellular symbiosis with temperate legumes. During symbiosis S. meliloti will fix atmospheric nitrogen, which it provides to its host plant. In return for fixed nitrogen, the plant provides its microsymbiont with carbon in the form of C4-dicarboxylates. Unlike most model organisms, S. meliloti prioritizes catabolism of succinate, a phenomenon referred to as succinate-mediated catabolite repression (SMCR). SMCR is controlled by an incomplete phosphotransferase system (PTS), which, unlike carbohydrate-type PTS, is a regulatory system that is not involved in sugar transport. This work uses a biochemical approach to elucidate the signals involved in regulating PTS activity. Biochemical characterization of S. meliloti EINtr revealed that the enzyme is inhibited by glutamine, a major signal of nitrogen availability in proteobacteria. EINtr detects glutamine through its N-terminal GAF domain, a ubiquitous small molecule binding domain. In contrast to E. coli EINtr, the S. meliloti enzyme is not activated by a-ketoglutarate. The differences in EINtrregulation likely reflect the preferred carbon source of each organism, with glucose entering central metabolism through glycolysis and succinate entering through the TCA cycle, sharing a metabolic pathway with a-ketoglutarate. Phosphorylated HPr-His in S. meliloti is much less stable than E. coli P~His-HPr, and this instability is due to an arginine residue that is conserved within a-proteobacteria that only contain an incomplete PTS. Rapid phosphohydrolysis of P~His-HPr in the a-proteobacteria may be act to remove phosphate from the system to avoid oversaturation, a problem that is not faced by sugar-phosphorylating PTS. The work presented here sheds light on how the PTS of S. meliloti integrates carbon, nitrogen, and energy levels within the cell in order to regulate SMCR

Whom to Groom and for What? Patterns of Grooming in Female Barbary Macaques <i>(Macaca sylvanus)</i>

<div><p>Grooming is one of the most conspicuous social interactions among nonhuman primates. The selection of grooming partners can provide important clues about factors relevant for the distribution of grooming within a social group. We analyzed grooming behavior among 17 semi-free ranging female Barbary macaques (<i>Macaca sylvanus</i>). We tested whether grooming is related to kinship, rank and friendship. Furthermore, we tested whether grooming is reciprocated or exchanged for rank related benefits (i.e. lower aggression and increased tolerance whilst feeding). We found that in general grooming was reciprocally exchanged, directed up the hierarchy and at the same time affected by friendship and kinship. Grooming was more frequent among individuals with higher friendship values as well as amongst related individuals. We also divided our data set on the basis of rank difference and tested if different power asymmetries between individuals affected the tendency to exchange grooming for rank related benefits and grooming reciprocation. In support of our initial hypothesis our results show that the reciprocation of grooming was a significant predictor of grooming interactions between individuals of similar rank, but not between those individuals more distantly separated in the social hierarchy. However, we did not find any evidence for grooming being exchanged for rank related benefits in either data set. Our results, together with previously published studies, illustrate the behavioral flexibility of macaques. It is clear that multiple studies of the same species are necessary to gather the data required for the solid comparative studies needed to shed light on patterns of grooming behavior in primates.</p></div

Results of LMMs testing grooming rate and grooming time and their relationship to kinship, rank distance, relative rank, friendship, grooming received, co-provisioning, aggression received and season among females with low rank distance.

<p>Variables with values in bold had significant effect on grooming rate or grooming time based on CI.</p><p>Results of LMMs testing grooming rate and grooming time and their relationship to kinship, rank distance, relative rank, friendship, grooming received, co-provisioning, aggression received and season among females with low rank distance.</p