Molecular Microbiology Research 2024, Vol.14, No.1, 61-64 http://microbescipublisher.com/index.php/mmr 62 2 Analysis of Experimental Data Figure 1 shows the relationship between bacterial community temperature index (CTI) and environmental temperature. Figure 1a shows a significant positive correlation between CTI and temperature in marine navigation samples from the southern hemisphere (n=1 946). Samples from different depth ranges exhibit consistent trends, with surface to 100 m (light blue), 100 m to 1 000 m (black), and samples above 1 000 m (orange) all showing an increase in CTI with increasing temperature. Figure 1b shows that the relationship between CTI and temperature varies slightly among different stations in the time series station sample of the IMO National Reference Station (NRS) (n=1 660). Dark orange represents the MAI site, light blue represents the ROT site, green represents the PHB site, deep purple represents the NSI site, light purple represents the YON site, and green represents the DAR site. Overall, the CTI of each site is positively correlated with temperature, but shows different slopes in different temperature ranges, indicating that the bacterial communities of each site have different temperature adaptability and niche preferences within a specific temperature range. Figure 1 The relationship between bacterial community temperature index and in situ environmental temperature Image caption: a: Samples collected spatially during oceanic voyages in the Southern Hemisphere (n = 1 946); b: Samples collected temporally at IMOS National Reference Stations (NRS) time-series sites around the Australian continental shelf (n = 1 660); Dashed red line represents a slope of one Figure 6 shows the impact of marine heatwaves (MHW) on the composition and structure of microbial communities. Figure 6a shows the bacterial genera that caused the greatest difference in microbial community composition under MHW and non MHW conditions in the same month, with high-temperature adaptive genera such as Synechococcus, Procholococcus, and Trichodesmum significantly increasing under MHW conditions. Figure 6b and Figure 6c indicate that MHW altered the seasonal variation of bacterial diversity index. The Shannon index and inverse Simpson index generally rose during the MHW period, especially during the hot season from February to April. Figure 6d shows a significant increase in the number of "rare" bacterial groups in the samples during the MHW period, especially during the peak heatwave period from February to April. These results indicate that MHW significantly altered the diversity and composition structure of microbial communities. 3 Analysis of Research Results The Tasman Sea marine heatwave (MHW) event in 2015/16 had a long duration and high intensity, while the MHW event in 2017/18 was relatively short and mild. In these two MHW events, there was a significant positive correlation between bacterial community temperature index (CTI) and in situ environmental temperature. In
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