Molds are fungi that grow in the form of multicellular filaments called hyphae. A connected network of these tubular branching hyphae, called a mycelium, is considered a single organism. The hyphae are generally transparent, so the mycelium appears like very fine, fluffy white threads over the surface. Cross-walls (septa)separate connected compartments along the hyphae, each containing one or more, genetically identical nuclei. The dusty texture of many molds is caused by profuse numbers of asexual spores called conidia formed by differentiation at the ends of hyphae. The shape, color and the way they are formed are used to classify the fungi.
Fungi that can adopt a single celled growth habit are called yeasts. Molds are considered to be microbes and do not form a specific taxonomic or phylogenetic grouping, but can be found in the divisions Zygomycota and Ascomycota. Molds biodegrade natural materials. They also play important roles in biotechnology and food science in the production of various foods, beverages, antibiotics, pharmaceuticals and enzymes. Some diseases of animals and humans can be caused by molds as a result of allergic sensitivity to their spores or toxic compounds.
Below is some information from the internet pulled together for your convenience in examining the possible origins of filamentous organisms. I have noticed that some specimens one might think are fibers are actually some type of worm so that’s another possibility for things that look like fibers.
Why Do Bacteria Filament?
February 04, 2008
Streptomyces coelicolor (false colored).
Source: Nora Ausmees, University of Uppsala
Some bacteria naturally grow as filaments, e.g., members of the actinomycetes. Many others, e.g., E. coli and B. subtilis, make filaments only when under stress─a fact that has been known for about one hundred years but is still a bit of a mystery.
Many kinds of stress can prompt this response, including DNA damage that elicits the SOS response, partial inhibition of cell wall synthesis by antibiotics, and the expression of certain thermosensitive mutations affecting cell division (called fts mutants for “filament forming temperature sensitive”). So general is this phenomenon that, over 30 years ago, we commented in a review: …it seems possible that any chemical at some concentration, whether attainable in the laboratory or not, can cause filament formation. (When the great geneticist, Rollin Hotchkiss, heard of this, he muttered: How depressing!) Be that as it may, filamentation is to bacteria what fever is to children.
Ultrathin section of an E. coli temperature-sensitive mutant grown at 42° for 45 minutes. Scale bar: 1mm. Source: Burdett, I. D. J. and R. G. E. Murray. 1974. Septum Formation in E. coli. J. Bacteriol. 119: 303-324Filaments, in both bacteria and fungi, result when rod-shaped cells cease to divide but continue to grow. In many cases, growth can continue for quite a while and at a rapid speed, resulting in long and often healthy-looking filaments. Nucleoids continue to segregate and are spaced normally along the filament. (Some folks like to call this polyploidy, but multinucleate seems more appropriate.) Apparently, under some circumstances, cell division is a dispensable process─at least for a while.
Schematic drawing of a mutant defective in decatenation of progeny chromosomes. The DNA does not segregate but remains as a mass in the center of the cell. Source: Schaechter, M., J. L. Ingraham, and F. C. Neidhardt. 2006. Microbe p.182.
To show how indifferent cell growth can be to whether a cell divides or not, cells also become filamentous when decatenation of their intertwined progeny chromosomes is inhibited by mutation or by drugs. Given the pleiotropic nature of the response, it has proven difficult to figure out why cell division is so much more delicate than the rest of the cell’s functions.For now, let’s leave questions of mechanism aside and ask instead, how this phenomenon matters in the ecology of these organisms. This question has recently been examined in an article from Scott Hultgren’s lab. The article goes a long way towards making sense of why bacteria might have developed such a strategy. It is pleasurable reading, illustrated with many exciting instances. Their examples suggest that filamentation can confer protection against grazing predators (including phagocytes in mammalian hosts), resistance to intracellular killing, swarming motility to evade immune cells, and insensitivity to some antibiotics and other inimical agents. Making filaments to avoid grazing by predatory protists is often seen in marine and other environments. In general, bacteria longer than 7 μm are inedible by many protists, and filamentation occurs in direct response to effectors produced by the predators. In other cases, e.g., in some Proteus, filamentation is part of their life cycle. These organisms “swarm” intermittently on agar as well as on the surface of catheters. The pathogenic E. coli that cause urinary tract infections invade the epithelial cells of the bladder, and there they transform into filaments some 50 times the normal length. This strategy enables these filamenting bacteria (and others) to survive engulfment by phagocytic cells. Also, at body temperatures, Legionella make phagocytosis-resistant biolfilms composed of filamentous cells.
Filamentous E. coli on infected mouse bladder cells. The bacteria were stained with a red fluorescent nucleic acid dye (ToPro3) and examined under a laser scanning confocal fluorescent microscope. Scale bar: 30 μm. Source: Justice, S. S., D. A. Hunstad, P. C. Seed, and S. J. Hultgren. 2006. Filamentation by E. coli subverts innate defenses during urinary tract infection. PNAS 103(52) 19884-19889.After completing their extensive survey, the authors conclude that filamentation is a survival tactic employed by diverse bacteria under a variety of conditions. Considering the reliance of some pathogens on filamentation, they suggest that drugs blocking filament formation may be useful against specific pathogens. We thank the authors for calling attention to the broad ecological aspects of this distinctive bacterial (and fungal) talent. I finish with an aside: the opposite of filamentation, i.e., division without growth, also occurs. In the lab, bacterial cells in stationary phase are generally smaller than growing ones. Likewise, most bacteria making a living in oligotrophic environments are on the small side, some so small as to merit the label nanobacteria. I recall once observing under the microscope the “growth” of E. coli on purified agar containing only phosphate buffer. Each cell divided three or four times, resulting in an average cell size 1/8 to 1/16 of the starting one! Filaments count, but so do numbers.
After completing their extensive survey, the authors conclude that filamentation is a survival tactic employed by diverse bacteria under a variety of conditions. Considering the reliance of some pathogens on filamentation, they suggest that drugs blocking filament formation may be useful against specific pathogens. We thank the authors for calling attention to the broad ecological aspects of this distinctive bacterial (and fungal) talent. I finish with an aside: the opposite of filamentation, i.e., division without growth, also occurs. In the lab, bacterial cells in stationary phase are generally smaller than growing ones. Likewise, most bacteria making a living in oligotrophic environments are on the small side, some so small as to merit the label nanobacteria. I recall once observing under the microscope the “growth” of E. coli on purified agar containing only phosphate buffer. Each cell divided three or four times, resulting in an average cell size 1/8 to 1/16 of the starting one! Filaments count, but so do numbers.
http://en.wikipedia.org/wiki/Filamentation Bacteria have complex systems to protect themselves but they alter this highly regulated process to transform into filamentous organisms in stressful environments, including sites of interaction with their hosts. Filamentation could be a response to specific environmental cues that promote survival amidst the threats of consumption and killing. In E. coli, cells continue to elongate but do not divide (no septa formation). Filamentation may be a reaction to DNA damage or inhibition of replication involving the SOS response which has been proposed as a model for bacterial evolution of certain types of antibioticc resistance. The SOS response elicits filamentation.
Filamentation of E. coli.