Review for Final Study old exams I will reuse rewrite some of those questions Review big themes see the rest of this lecture and last lecture Remember from lec 2 Kluyver and van Niel proposed that all respiratory reactions aerobic and anaerobic could be summarized using the simple formula AH2 B A BH2 Aerobic Resp For Beggiatoa example of aerobic respiration SH2 O2 So H2O For aerobic chemoheterotrophs example of aerobic respiration CH2O O2 CO2 H2O Anaerobic respiration Same thing but with a different e acceptor AH2 B A BH2 For anaerobic chemoheterotrophs anaerobic respiration CH2O NO3 CO2 N2O See Fig 6 8 All catabolic reactions are oxidation reduction reactions it s all about movement of electrons An extreme illustration of this is Geobacter sulfurreducens Delta Proteobacteria it can use metal electrodes as electron acceptors for anaerobic respiration It is now being tested in microbial fuel cells to generate electricity It can use acetate as its edonor thus electrical current production is dependent upon oxidation of acetate to carbon dioxide Acetate metal surface electrical current flows to side of the battery Please read the abstract to this paper Electricity Production by Geobacter sulfurreducens Attached to Electrodes Appl Environ Microbiol 69 1548 1555 D R Bond D R Lovley Full paper is on class web site Electricity Production by Geobacter sulfurreducens Attached to Electrodes Appl Environ Microbiol 69 15481555 D R Bond D R Lovley Previous studies have suggested that members of Geobacter can use electrodes as electron acceptors for anaerobic respiration In order to better understand this electron transfer process for energy production G sulfurreducens was inoculated into chambers in which a graphite electrode served as the sole electron acceptor and acetate or hydrogen was the electron donor The electron accepting electrodes were maintained at oxidizing potentials by connecting them to similar electrodes in oxygenated medium fuel cells or to potentiostats that poised electrodes at 0 2 V versus an Ag AgCl reference electrode poised potential When a small inoculum of G sulfurreducens was introduced into electrode containing chambers electrical current production was dependent upon oxidation of acetate to carbon dioxide and increased exponentially indicating for the first time that electrode reduction supported the growth of this organism When the medium was replaced with an anaerobic buffer lacking nutrients required for growth acetate dependent electrical current production was unaffected and cells attached to these electrodes continued to generate electrical current for weeks This represents the first report of microbial electricity production solely by cells attached to an electrode Electrode attached cells completely oxidized acetate to levels below detection 10 M and hydrogen was metabolized to a threshold of 3 Pa The rates of electron transfer to electrodes 0 21 to 1 2 mol of electrons mg of protein min were similar to those observed for respiration with Fe III citrate as the electron acceptor Eo 0 37 V The production of current in microbial fuel cell 65 mA m2 of electrode surface or poised potential 163 to 1 143 mA m2 mode was greater than what has been reported for other microbial systems even those that employed higher cell densities and electron shuttling compounds Since acetate was completely oxidized the efficiency of conversion of organic electron donor to electricity was significantly higher than in previously described microbial fuel cells These results suggest that the effectiveness of microbial fuel cells can be increased with organisms such as G sulfurreducens that can attach to electrodes and remain viable for long periods of time while completely oxidizing organic substrates with quantitative transfer of electrons to an electrode As an illustration Rabbits in Australia Rabbits were first introduced to Australia from England in 1859 Because they had no natural enemies they soon became major pests Finally in 1950 a scientist isolated a Myxoma virus that caused a not very serious disease in a species of Brazilian rabbits When this virus was brought to Australia it was a new disease to those English rabbits it was extremely virulent to them Within a year 99 9 of all the rabbits in Australia died Over the following 20 years scientists closely monitored the coevolution of this new disease and the rabbits of Australia The main finding of these studies was that the virulence of the virus decreased each year and the resistance of the rabbits increased Finally after about ten years the number of rabbits in Australia increased back up to about 20 of their pre virus levels Evolution of diseases In many cases the longer a population is exposed to a pathogen the less susceptible that population is to the disease Over the short term months to years this is due to the fact that more hosts become immune Over the long term this is due to natural selection which tends to weed out extremely virulent pathogens because if they kill all of their hosts then they too will go extinct Simultaneously hosts that are more resistant to a prevalent pathogen have more offspring Thus through evolutionary time specific pathogens tend to become less virulent to their hosts become more resistant to their pathogens It is thought that some non pathogenic relationships evolved from former antagonistic ones via a progression like this Pathogenic Commensalistic Mutualistic Two important points about the above story 1 The long term change in the rabbits was genetic i e more resistant rabbits were selected for 2 It took about ten rabbit generations assuming 1 generation per year for the rabbits and virus to reach a equilibrium in which the rabbit was quite resistant and the virus was much less virulent Let s quickly review that with an overhead Of course not all diseases evolve exactly like the rabbit myxoma case Co evolution is a back and forth process that can lead to a balance as in the rabbit myxoma case or to either the pathogen or the host gaining advantage at any point in time And evolution can lead to re emergence of diseases like the flu plague and other diseases we have discussed Emerging Infectious Diseases The rabbit story is pertinent to how and why new diseases keep cropping up see Lecture 23 From Lec 23 Fig 20 10 Some emerging infectious diseases Most are old diseases that are re emerging or diseases that jump from animals to humans HIV Ebola Some reasons for emerging diseases climate