4-Appendix_E-_Microorganism_Report_revised.pdf

To Mary Slater 07/10/2011

Fort Point Add Services

Project 09062.17 Fort Point National Historic Site

Architectural Resources Group

Pier 9, The Embarcadero

San Francisco Ca 94111

From Mary‐Lou Florian PhD

Conservation Scientist

Research Associate Royal BC Museum

Home 133 Simcoe St, Victorian BC

V8V 1K5 Canada

Identification of microorganism in three samples from brick structures and their effects on substrates.

Sample No 1

It is a community of a green algae and blue green cyanobacteria.

The green algae Protococcus (Chlorococcum) sp, is single celled and 20‐30µm in diameter. Some cells shows fission into two cells. It has a thick exocellular film, which gives it its slimy characteristic. The cells are clumped together because of this slime. The cells show the characteristic bright green of green algae. This is the most common green algae species found on damp cement surfaces.

Sample 1, Protococcus

(Chlorococcum) sp

There are another smaller group of cells which are most probably the blue green cyanobacteria are Synechocystis sp. It would require DNA analyses for verification. I at first thought it might be the common green algae Chlorella but the cell size is smaller and the characteristic cup shaped chloroplast was not observed. It has well separated single cells. The cell diameter is less than 5 µm. It has a slight blue green cast. The cells do not have an obvious exocellular film. Synechocystis sp. is common in fresh water ponds, but has been found in muddy soil and marine exposed church surfaces. It has the ability to live heterotrophically in the dark and phototropically in light.

The influence on the substrate is mainly due to their physical presence. The Protococcus slime is a colloid rich in polysaccharides. It acts as an adhesive for the cells to attach to a substrate, as a buffer between the cell and the environment and also controls moisture relationships between the cell and environment. In doing the latter it swells when hydrated and shrinks on drying. Because it is adhered to substrate material it is reported to disaggregate particles on shrinking and penetrate deep into the porosity of the rock when hydrated and viscose. The slime, when hydrated, it may influence the rate of solubilization of materials of the rock.

It is a polysaccharide and is considered as a ready source of carbon molecules for heterotrophic bacteria. If left on the surface it is considered to recondition the surface for new infestations. In maintenance it is desirable to not only remove the cells but also the slime‐ exocellular film. It is alkaline soluble and some will be dissolved by alkaline bleach or other alkaline washing solutions. Some may still stay in the rock pores. Mortar and cement are very porous; brick porosity is less porous but it varies with formulation and method of firing.

A cleaned cement surface, but with some viable cells still present, remaining in its original environment, a new algal film formation can occur within several months. But if all cells are killed it will take several years before a new film is formed, unless the environment is changed.

Sample No.2

It is the orange /green algae Trentopholia aurea. It is a cosmopolitan alga that grows in large filament mats in maritime environments, especially in foggy regions. It is green algae and when first formed the filaments are green but surface filaments become orange because of carotene development.

It is common on cement seaside walls, trees and other vegetation close to the sea. It is common in

Monterey Bay on cypress trees. The sample showed a sparse scattering of melanin pigmented fungal hyphae, and single celled green algae which probably were air born and caught in the algal extensive mat.

This species has been tested to determine if it precipitates calcium carbonate and it was shown not to precipitate calcium. It has a loose attachment to its substrate, probably with the help of old polysaccharide films or algae present. Each filament will be covered by a thin slimy exocellular film which will also aid attachment. But it has little to hold itself weight to a horizontal surface and as seen in the photos parts have fallen off. The algal mat requires some covering during removal because it may easily fall. It is commonly in trees where it has interstices to sew itself on to surfaces. It easily fragments and easily becomes air borne and with such large algal mat may present a health hazard such as hay fever, or asthma.

The impact on the brick and mortar surface has not been assessed but it will retain moisture which will increase the rate of chemical reactions and eventually increase solubility of rock substrates, but slowly.

Sample 2, Trentopholia aurea

Sample No. 3

It is the common yellow lichen Xanthoria parietina. It is foliose lichen composed of a fungus and single celled green algae species. The fungus is in a symbiotic relationship with green algae. It is located well below the surface. The lichen has smooth lobes, circa 1‐4mm, apothecia with asci and bicellular ascospores. The surface lobes are made of intertwined fungal hyphae.

This lichen is common in sunny exposed maritime environments on rock surfaces, fence posts and building ledges where birds roost. The horizontal ledge, it is on, is characteristic of such places. The species is always located in a high nitrogen environment, the nitrogen coming from bird faeces. It has many folk names Maritime Sunburst, Wall Lichen etc. The yellow color is from the pigment parietin.

It does not precipitate calcium carbonate or produce calcium oxalate‐ that many lichen on rock surfaces commonly do. It has a high level of potassium used in protection against an austere environment. It has a delicate, under developed rhizine (root‐like hyphae) thus it is easily dislodged.

This lichen species is present because of the high nitrogen of bird droppings. To prevent birds roosting, a physical obstruction for bird roosting would be logical. This lichen is not likely to influence the mortar physically but it will retain moisture increasing the rate of normal rock solubilization.

Sample 3, Xanthoria parietina

Scanning Electron Microscope (SEM) image of Sample 3, Xanthoria parietina, showing characteristic lobes.

What is the long‐term effect of these microorganisms on the brick substrates in a natural environment?

As we are all aware, these organisms are a part of natural changes of rock that allow recycling of materials. Geological material is eventually turned to dust and dust to molecules and molecules to ions that sustain life. Earth’s rock is destroyed and new rock formed by volcanic activity. Man‐made bricks and mortar are like natural rock geological substrates for microorganisms. The microorganisms may not directly impact the substrate, but just their physical presence changes it. It can increases moisture retention, alter substrate temperatures by shading, physically disaggregate of substrate particles, etc. In conservation of brick and mortar substrates in a natural environment, the best we can do is to slow down the process. Specific activities of the identified microorganism are discussed under each microorganism above.

Slowing down the process can be accomplished by simple maintenance involving removal and prevention of the microbial infestations. Prevention can be accomplished by altering the environment, such as preventing: birds roosting; moisture penetration into the substrate; deflecting wind or increasing aeration; altering light, etc. Unfortunately different microorganism species will be ready to take over in the changed environment ‐ there is a microorganism for everything. The Egyptians entombed bodies and their material belongings that helped them to retain some of their physical structure for centuries‐ until man disrupted these entombments. This environment allowed some original deterioration but none after they became void of oxygen, moisture, and light, and the temperature was constant. We can’t do this with our heritage that we need to see or are in nature. .

Maintenance involves the removal of the infestation. First safety issues have to be addressed.

The profuse growth of the orange algae on the underside of the brick structure presents a health hazard. Anyone entering this area should wear a particulate mask. A hepa filter is not necessary because the algal filaments and cells are too large to penetrate a particulate mask. There is no record of allergic responses but because of the large amount of hyphal mass and its potential to become air born, protection is logical. Also such algal mats can harbour mites and other small insects that one should protect themselves from. Gloves should be worn.

Removal of biofilms.

In the process of removal of the algal mat, algal film or lichens, all precautions have to be taken to prevent further contamination of clean areas and outside areas. This requires that the microorganisms should be killed prior to any physical removal. Washing with brushes simple redistributes the cells, power washing sprays it in all directions contaminating many new surfaces.

Power washing also physically impacts the surface and may embed microorganisms into the surface.

In dealing with algal film on cement and mortar surfaces, the common chemical, 5% commercial bleach, has been used to kill cells. It is reported not to have an effect on calcium based substrates; its pH is around 8. Its alkalinity also assists in removal of the polysaccharide film. I have used

70% isopropyl alcohol on green alga films. It killed the algae cells turning them light brown. The liquid alcohol was applied on the vertical wall allowing it to run down the surface and penetrate the substrate, using a plastic solvent wash bottle (a squeeze bottle with a hooked nozzle). Spraying is not logical.

Both bleach and alcohol are toxic, Safety issues have to be addressed. Doing a little at a time is better than doing a large area all at once. After the cells are dead it seems logical to remove as much as possible with a dry vacuum with a soft brush. The canister with the exhaust should be placed outside the area being treated. A hepa filter on the vacuum is recommended. After dry removal on the surfaces, a wet washing method, using bleach or other alkaline solution, can be used to remove remaining microorganism and as much a of the slimy exocellular film that remains. I am not advising you to do this it is up to a conservator to decide what can be done according to the substrate, but the steps of killing, dry vacuuming and wet washing seems the best approach.

So many reports of increase in lichen and algae activity on rock surfaces have been blamed on global warming but in fact they are a result of inappropriate cleaning procedures.