Why I lichen

Introduction to Lichens – An Alliance Between Kingdoms

Lichens are unusual creatures. A lichen is not a single organism the way most other living things are, but rather it is a combination of two organisms which live together intimately. Most of the lichen is composed of fungal filaments, but living among the filaments are algal cells, usually from a green alga or a cyanobacterium.

In many cases the fungus and the alga which together make the lichen may each be found living in nature without its partner, but many other lichens include a fungus which cannot survive on its own — it has become dependent on its algal partner for survival. In all cases though, the appearance of the fungus in the lichen is quite different from its morphology as a separately growing individual.

Lichens occur in one of four basic growth forms, as illustrated below:

  • crustose – crust-like, growing tight against the substrate.
  • squamulose – tightly clustered and slightly flattened pebble-like units.
  • foliose – leaflike, with flat sheets of tissue not tightly bound.
  • fruticose – free-standing branching tubes.

Lichen Morphology

Despite the wide diversity of the basic growth forms, all lichens have a similar internal morphology. The bulk of the lichen’s body is formed from filaments of the fungal partner, and the relative density of these filaments defines the layers within the lichen.

At its outer surface, where it comes in contact with the environment, the filaments are packed tightly together to form the cortex. The dense cortex serves to keep out other organisms, and helps to reduce the intensity of light which may damage the alga cells.

The algal partner cells are distributed just below the cortex in a layer where the fungal filaments are not so dense. This is very similar to the arrangement in a plant leaf, where the photosynthetic cells are loosely packed to allow air circulation.

Below the algal layer is the medulla, a loosely woven layer of fungal filaments. In foliose lichens, there is a second cortex below the medulla, but in crustose and squamulose lichens, the medulla is in direct contact with the underlying substrate, to which the lichen is attached.

Lichen layers

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Introduction to Lichens

Sticky Rolls-2020.05.19

Biofilm Related Disease – Biofilm formation represents a protected mode of growth that renders bacterial cells less susceptible to antimicrobials and to killing by host immune effector mechanisms and so enables the pathogens to survive in hostile environments and also to disperse and colonize new niches.

Biofilms: A microbial home – This essay provides a detailed insight into the properties and mechanisms of the development of abnormal condition, detection and removal of these microbial biofilms.

The pH of the Skin Surface and Its Impact on the Barrier Function – The ‘acid mantle’ of the stratum corneum seems to be important for both permeability barrier formation and cutaneous antimicrobial defense. The pH of the skin follows a sharp gradient across the stratum corneum, which is suspected to be important in controlling enzymatic activities and skin renewal. The skin pH is affected by a great number of endogenous factors, e.g. skin moisture, sweat, sebum, anatomic site, genetic predisposition and age.

Temperature and pH Affect the Production of Bacterial Biofilm – The human vagina has an average temperature of about 37.5 °C (99.5 °F) and a healthy pH range of between 3.8 and 4.5. A study looked at biofilm formation of a few different bacteria at 30°C and 37°C, and a pH of 5.5, 7.5 and 8.5.

Findings of the study

Bacterial strains studied were

  • Pseudomonas aeruginosa
  • Klebsiella pneumoniae
  • Vibrio cholerae

These bacteria are known to cause i) general infections in humans including skin and ear infections, ii) pneumonia, and iii) cholera. These bacteria are known to produce biofilms.

The impact of temperature on biofilm production

A decrease in biofilm production was observed at 37°C in eight of the tested strains, compared to production at 30°C. Biofilm production still existed at both temperatures. At normal human vaginal temperatures, biofilm activity exists.

Five of the strains tested had increased biofilm activity at 37°C compared to at 30°C.

The impact of pH on biofilm production

The increases in biofilm formation from a pH of 5.5 were sometimes up to 300 per cent. Increased pH (more alkaline) lead to higher biofilm production.

The results are clear – alkaline pH encourages biofilm formation.

Bacterial biofilm and associated infections.

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Microscopic entities, microorganisms that drastically affect human health need to be thoroughly investigated. A biofilm is an architectural colony of microorganisms, within a matrix of extracellular polymeric substance that they produce. Biofilm contains microbial cells adherent to one-another and to a static surface (living or non-living). Bacterial biofilms are usually pathogenic in nature and can cause nosocomial infections. The National Institutes of Health (NIH) revealed that among all microbial and chronic infections, 65% and 80%, respectively, are associated with biofilm formation.Candida Biofilm

The process of biofilm formation consists of many steps, starting with attachment to a living or non-living surface that will lead to formation of micro-colony, giving rise to three-dimensional structures and ending up, after maturation, with detachment. During formation of biofilm several species of bacteria communicate with one another, employing quorum sensing. In general, bacterial biofilms show resistance against human immune system, as well as against antibiotics. Health related concerns speak loud due to the biofilm potential to cause diseases, utilizing both device-related and non-device-related infections. In summary, the understanding of bacterial biofilm is important to manage and/or to eradicate biofilm-related diseases.