Week Summary

On Monday of this week, we streaked the remaining starch plates that we were unable to do the week before. Then we made observations of the growth of our strands in the liquid media. We scored them from 0 to ++++. We had growth in all of our samples ranging from + (included 59, 73, 74, 64, 65, and 78) up to ++++ (included 54, 56, 67, 69, and 70). Sample 68 was contaminated. So some of the stock culture was again placed in PCB liquid media and will be checked again in 20 days. Then we counted cultures on irradiated Gobi-1 samples, and found that MA had by far the lowest CFU/g of only 6.6x10². On the un-irradiated samples, MA had a CFU/g value of 9.7x10³, giving it only 6.9% survival. This may have occurred because most of the bacteria that require salt have a low irradiation tolerance. For the other irradiated samples we found that PCA had a CFU/g of 1.1x10³ with a 48.1% survival, 1/10 PCA had a CFU/g 7.63x10³ with a 74.8% survival, and 1/100 PCA had a CFU/g of 1.32x10^4 with a 227.6% survival. 1/100 PCA's unusual percent survival may have occurred because the irradiation inhibited the growth a bacteria that dominated the un-irradiated samples. In general, the irradiation had lower number of colonies, but with most of our samples having high survival percentages most of our bacteria have a high irradiation tolerance. Also, because 1/100 PCA had the highest CFU/g value, this may show that the irradiation resistant bacteria prefer low nutrients.

On Wednesday, we observed and recorded the results from the temperature and salt experiments with our stands. We streaked new stock cultures from the 25ºC samples. Culture #59 and #69 had contamination in the temperature. So from the second stock culture we re-streaked the temperature trials. Also, #68 had enough growth on our stock culture. So we streaked the temperature and salt trials. The results from the salt plates showed that all the bacteria can live up to 3% except for #72 and #77. Only eight of our strands were able to survive up to 9% (58, 59, 61, 62, 63, 64, 73, and 74). Overall, most are the bacteria are fairly sensitive to higher concentrations of salt. The results from the temperature plates showed that all the strands except six (64, 66, 70, 71, 72, 74) could survive at temperatures as low as 10ºC. While only 55, 63, and 74, couldn't survive at 37ºC, and 53, 54, 57, 58, 60, 72, 75, 76, and 78 were all able to withstand temperatures as high as 42ºC.

An interesting observation is that #74 had a small temperature range only growing at 25ºC and 30ºC, but it grew in media that contained 9% NaCl. Being that it was orange in color, I compared it to the two Blastococcus species ( B. saxobsidens and B. jejuensis ). According to the Urzi et al 2004 paper, Blastococcus saxobsidens has a temperature growth range of 20-37ºC, and it was reported to have grown on 5% NaCl. These similar traits with further tests may reveal that #74 is Blastococcus saxobsidens.