Caloric restriction causes symmetric cell division and delays aging in Escherichia coli

Aging is one of the most intriguing processes of biology and despite decades of research, many aspects of aging are poorly understood. Aging is known to occur in bacteria and yeast that divide with morphological asymmetry. Morphologically symmetrically dividing bacteria such as _Escherichia coli_ were assumed not to age until they were shown to divide with functional asymmetry leading to aging and death of some of the cells even in exponentially growing cultures. In asymmetrically dividing _E. coli_ the newly synthesized components are presumed to occupy one pole so that after division one of the daughter cells receives newly synthesized components whereas the other retains the older components. Mathematical models predicted that at the population level, asymmetric growth should result in higher growth rate and symmetric growth in higher growth yield. Therefore, arguably symmetric cell division should be selected in low nutrient environments and asymmetric division in nutrient rich environments. A further prediction was that lower substrate concentrations should strengthen repair mechanisms and suppress aging whereas higher substrate concentrations suppress repair and enhance aging. We show here that _E. coli_ divides more symmetrically under caloric restriction, that both genetic selection and phenotypic plasticity are important determinants of cell division symmetry and also that the proportion of cells that stop dividing and therefore are presumably dead is significantly lower in symmetrically dividing cultures. However, contrary to the prediction, symmetry was not always accompanied by reduced growth rate. These results demonstrate that asymmetry of division in _E. coli_ is not hardwired but responsive to the nutritional environment. This provides a new perspective on why caloric restriction increases lifespan in organisms ranging from microbes to mammals. Symmetry of division may be a mechanism spanning across the width of life forms but regulating aging in different ways in different forms

_Streptomyces_ sp. as predators of bacteria

Background: The ecological role of actinomycetes and their secondary metabolites is not yet completely understood. 
Hypothesis: Actinomycetes and Streptomyces sp. in particular, are non-obligate predators of bacteria in soil. 
Evidence: Ability to grow on live bacterial cells as a sole source of nutrients. Prey cell lysis accompanying growth. Circumstantial evidence for the involvement of antimicrobials along with enzymes.
Implications: This finding may open up a new source of novel secondary metabolites from the genus

Evolutionary origins of insulin resistance: a behavioral switch hypothesis

<p>Abstract</p> <p>Background</p> <p>Insulin resistance, which can lead to a number of diseases including type 2 diabetes and coronary heart disease, is believed to have evolved as an adaptation to periodic starvation. The "thrifty gene" and "thrifty phenotype" hypotheses constitute the dominant paradigm for over four decades. With an increasing understanding of the diverse effects of impairment of the insulin signaling pathway, the existing hypotheses are proving inadequate.</p> <p>Presentation of the hypothesis</p> <p>We propose a hypothesis that insulin resistance is a socio-ecological adaptation that mediates two phenotypic transitions, (i) a transition in reproductive strategy from "r" (large number of offspring with little investment in each) to "K" (smaller number of offspring with more investment in each) and (ii) a transition from "stronger to smarter" or "soldier to diplomat" i.e. from relatively more muscle dependent to brain dependent lifestyle. A common switch could have evolved for the two transitions since the appropriate environmental conditions for the two transitions are highly overlapping and interacting.</p> <p>Testing the hypothesis</p> <p>Gestational insulin resistance diverts more energy through the placenta, resulting in increased investment per offspring. On the other hand, insulin resistance is associated with reduced ovulation. The insulin signaling pathway is also related to longevity. Insulin resistance diverts more nutrients to the brain as compared to muscle. Also, hyperinsulinemia has direct positive effects on cognitive functions of the brain. The hypothesis gets support from known patterns in human clinical data and recent research on the molecular interactions in the insulin signaling pathway. Further we state many predictions of the hypothesis that can be tested experimentally or epidemiologically.</p> <p>Implications of the hypothesis</p> <p>The hypothesis can bring about a significant change in the line of treatment as well as public health policies for the control of metabolic syndrome.</p

Longevity of Azotobacter cysts and a model for optimization of cyst density in liquid bioinoculants

Species of Azotobacter are known to form heat and desiccation-resistant cysts that have a long life span. Recently this property has been used to prepare nitrogen-fixing liquid bioinoculants useful for a variety of crops. The survival of Azotobacter cysts were determined in a liquid medium in order to estimate the shelf-life of a liquid cyst bioinoculant. A negative exponential model was fitted to the survivorship curve. The death rate increased with the initial density of cysts and ranged from 0.02 to 0.05 per month. The nitrogen-fixing ability dropped after two years. It was concluded that the shelf-life of cyst bioinoculants should be decided by the nitrogen-fixing ability rather than cyst survival. Based on the derived kinetics a model for optimization of cyst density in Azotobacter cyst-based liquid bioinoculants is proposed

The co-optimization of floral display and nectar reward

In most insect-pollinated flowers, pollinators cannot detect the presence of nectar without entering the flower. Therefore, flowers may cheat by not producing nectar and may still get pollinated. Earlier studies supported this 'cheater flower' hypothesis and suggested that the cost saving by cheater flowers could be the most predominant selective force in the evolution of nectarless flowers. Previous models as well as empirical studies have addressed the problem of optimizing the proportion of nectarless and nectarful flowers. However, there has been no attempt to optimize the investment in nectar production along with that in floral display. One of the key questions that arises is whether the floral display will evolve to be an honest indicator of nectar reward. We use a mathematical model to cooptimize the investments in nectar and floral display in order to achieve maximum reproductive success. The model assumes that pollinators rely on a relative rather than an absolute judgement of reward. A conspicuous floral display attracts naive pollinators on the one hand and enhances pollinator learning on the other. We show that under these assumptions, plant-pollinator co-evolution leads to honest signalling, i.e. a positive correlation between display and reward

A new antibacterial imidazole from the marine sponge Iricinia fusca

A new imidazole alkaloid (1) along with two known compounds, variabilin (2) and iricinialactam A (3) have been isolated from the Arabian marine sponge Ircinia fusca. The structure of the new compound was established as 4-((1, 2-dihydroxy-5-(methyl (1-methyl-1H-imidazol-4-yl) amino) pentan-3-yl) oxy)-3, 5-dimethoxy-1-methylpyrrolidin-2-one (1) by 1D and 2D NMR, and high-resolution electrospray ionization mass spectrometry (HRESIMS). Compound 1 exhibited selective growth inhibitory activity against gram-positive bacteria S. aureus at 100 µg/mL

Blackmailing: the keystone in the human mating system

<p>Abstract</p> <p>Background</p> <p>The human mating system is characterized by bi-parental care and faithful monogamy is highly valued in most cultures. Marriage has evolved as a social institution and punishment for extra pair mating (EPM) or adultery is common. However, similar to other species with bi-parental care, both males and females frequently indulge in EPM in secrecy since it confers certain gender specific genetic benefits. Stability of faithful monogamy is therefore a conundrum. We model human mating system using game theory framework to study the effects of factors that can stabilize or destabilize faithful committed monogamy.</p> <p>Results</p> <p>Although mate guarding can partly protect the genetic interests, we show that it does not ensure monogamy. Social policing enabled by gossiping is another line of defense against adultery unique to humans. However, social policing has a small but positive cost to an individual and therefore is prone to free riding. We suggest that since exposure of adultery can invite severe punishment, the policing individuals can blackmail opportunistically whenever the circumstances permit. If the maximum probabilistic benefit of blackmailing is greater than the cost of policing, policing becomes a non-altruistic act and stabilizes in the society. We show that this dynamics leads to the coexistence of different strategies in oscillations, with obligate monogamy maintained at a high level. Deletion of blackmailing benefit from the model leads to the complete disappearance of obligate monogamy.</p> <p>Conclusions</p> <p>Obligate monogamy can be maintained in the population in spite of the advantages of EPM. Blackmailing, which makes policing a non-altruistic act, is crucial for the maintenance of faithful monogamy. Although biparental care, EPM, mate guarding and punishment are shared by many species, gossiping and blackmailing make the human mating system unique.</p

Patterns in abundance and diversity of faecally dispersed parasites of tiger in Tadoba National Park, central India

BACKGROUND: Importance of parasites in ecological and evolutionary interactions is being increasingly recognized. However, ecological data on parasites of important host species is still scanty. We analyze the patterns seen in the faecal parasites of tigers in the Tadoba National Park, India, and speculate on the factors and processes shaping the parasite community and the possible implications for tiger ecology. RESULTS: The prevalence and intensities were high and the parasite community was dominated by indirect life cycle parasites. Across all genera of parasites variance scaled with the square of the mean and there was a significant positive correlation between prevalence and abundance. There was no significant association between different types of parasites. CONCLUSIONS: The 70 samples analyzed formed 14 distinct clusters. If we assume each of the clusters to represent individual tigers that were sampled repeatedly and that resident tigers are more likely to be sampled repeatedly, the presumed transient tigers had significantly greater parasite loads than the presumed resident ones

Sociobiological Control of Plasmid copy number

Background:&#xd;&#xa;All known mechanisms and genes responsible for the regulation of plasmid replication lie with the plasmid rather than the chromosome. It is possible therefore that there can be copy-up mutants. Copy-up mutants will have within host selective advantage. This would eventually result into instability of bacteria-plasmid association. In spite of this possibility low copy number plasmids appear to exist stably in host populations. We examined this paradox using a computer simulation model.&#xd;&#xa;&#xd;&#xa;Model:&#xd;&#xa;Our multilevel selection model assumes a wild type with tightly regulated replication to ensure low copy number. A mutant with slightly relaxed replication regulation can act as a &#x201c;cheater&#x201d; or &#x201c;selfish&#x201d; plasmid and can enjoy a greater within-host-fitness. However the host of a cheater plasmid has to pay a greater cost. As a result, in host level competition, host cell with low copy number plasmid has a greater fitness. Furthermore, another mutant that has lost the genes required for conjugation was introduced in the model. The non-conjugal mutant was assumed to undergo conjugal transfer in the presence of another conjugal plasmid in the host cell.&#xd;&#xa;&#xd;&#xa;Results:&#xd;&#xa;The simulatons showed that if the cost of carrying a plasmid was low, the copy-up mutant could drive the wild type to extinction or very low frequencies. Consequently, another mutant with a higher copy number could invade the first invader. This process could result into an increasing copy number. However above a certain copy number within-host selection was overcompensated by host level selection leading to a rock-paper-scissor (RPS) like situation. The RPS situation allowed the coexistence of high and low copy number plasmids. The non-conjugal &#x201c;hypercheaters&#x201d; could further arrest the copy numbers to a substantially lower level.&#xd;&#xa;&#xd;&#xa;Conclusions:&#xd;&#xa;These sociobiological interactions might explain the stability of copy numbers better than molecular mechanisms of replication regulation alone

Phenotypic Plasticity and Effects of Selection on Cell Division Symmetry in Escherichia coli

Aging has been demonstrated in unicellular organisms and is presumably due to asymmetric distribution of damaged proteins and other components during cell division. Whether the asymmetry-induced aging is inevitable or an adaptive and adaptable response is debated. Although asymmetric division leads to aging and death of some cells, it increases the effective growth rate of the population as shown by theoretical and empirical studies. Mathematical models predict on the other hand, that if the cells divide symmetrically, cellular aging may be delayed or absent, growth rate will be reduced but growth yield will increase at optimum repair rates. Therefore in nutritionally dilute (oligotrophic) environments, where growth yield may be more critical for survival, symmetric division may get selected. These predictions have not been empirically tested so far. We report here that Escherichia coli grown in oligotrophic environments had greater morphological and functional symmetry in cell division. Both phenotypic plasticity and genetic selection appeared to shape cell division time asymmetry but plasticity was lost on prolonged selection. Lineages selected on high nutrient concentration showed greater frequency of presumably old or dead cells. Further, there was a negative correlation between cell division time asymmetry and growth yield but there was no significant correlation between asymmetry and growth rate. The results suggest that cellular aging driven by asymmetric division may not be hardwired but shows substantial plasticity as well as evolvability in response to the nutritional environment