Abstract: —J. BLUNDEN, T. BOYER, AND E. BARTOW-GILLIES Earth’s global climate system is vast, complex, and intricately interrelated. Many areas are influenced by global-scale phenomena, including the “triple dip” La Niña conditions that prevailed in the eastern Pacific Ocean nearly continuously from mid-2020 through all of 2022; by regional phenomena such as the positive winter and summer North Atlantic Oscillation that impacted weather in parts the Northern Hemisphere and the negative Indian Ocean dipole that impacted weather in parts of the Southern Hemisphere; and by more localized systems such as high-pressure heat domes that caused extreme heat in different areas of the world. Underlying all these natural short-term variabilities are long-term climate trends due to continuous increases since the beginning of the Industrial Revolution in the atmospheric concentrations of Earth’s major greenhouse gases. In 2022, the annual global average carbon dioxide concentration in the atmosphere rose to 417.1±0.1 ppm, which is 50% greater than the pre-industrial level. Global mean tropospheric methane abundance was 165% higher than its pre-industrial level, and nitrous oxide was 24% higher. All three gases set new record-high atmospheric concentration levels in 2022. Sea-surface temperature patterns in the tropical Pacific characteristic of La Niña and attendant atmospheric patterns tend to mitigate atmospheric heat gain at the global scale, but the annual global surface temperature across land and oceans was still among the six highest in records dating as far back as the mid-1800s. It was the warmest La Niña year on record. Many areas observed record or near-record heat. Europe as a whole observed its second-warmest year on record, with sixteen individual countries observing record warmth at the national scale. Records were shattered across the continent during the summer months as heatwaves plagued the region. On 18 July, 104 stations in France broke their all-time records. One day later, England recorded a temperature of 40°C for the first time ever. China experienced its second-warmest year and warmest summer on record. In the Southern Hemisphere, the average temperature across New Zealand reached a record high for the second year in a row. While Australia’s annual temperature was slightly below the 1991–2020 average, Onslow Airport in Western Australia reached 50.7°C on 13 January, equaling Australia's highest temperature on record. While fewer in number and locations than record-high temperatures, record cold was also observed during the year. Southern Africa had its coldest August on record, with minimum temperatures as much as 5°C below normal over Angola, western Zambia, and northern Namibia. Cold outbreaks in the first half of December led to many record-low daily minimum temperature records in eastern Australia. The effects of rising temperatures and extreme heat were apparent across the Northern Hemisphere, where snow-cover extent by June 2022 was the third smallest in the 56-year record, and the seasonal duration of lake ice cover was the fourth shortest since 1980. More frequent and intense heatwaves contributed to the second-greatest average mass balance loss for Alpine glaciers around the world since the start of the record in 1970. Glaciers in the Swiss Alps lost a record 6% of their volume. In South America, the combination of drought and heat left many central Andean glaciers snow free by mid-summer in early 2022; glacial ice has a much lower albedo than snow, leading to accelerated heating of the glacier. Across the global cryosphere, permafrost temperatures continued to reach record highs at many high-latitude and mountain locations. In the high northern latitudes, the annual surface-air temperature across the Arctic was the fifth highest in the 123-year record. The seasonal Arctic minimum sea-ice extent, typically reached in September, was the 11th-smallest in the 43-year record; however, the amount of multiyear ice—ice that survives at least one summer melt season—remaining in the Arctic continued to decline. Since 2012, the Arctic has been nearly devoid of ice more than four years old. In Antarctica, an unusually large amount of snow and ice fell over the continent in 2022 due to several landfalling atmospheric rivers, which contributed to the highest annual surface mass balance, 15% to 16% above the 1991–2020 normal, since the start of two reanalyses records dating to 1980. It was the second-warmest year on record for all five of the long-term staffed weather stations on the Antarctic Peninsula. In East Antarctica, a heatwave event led to a new all-time record-high temperature of −9.4°C—44°C above the March average—on 18 March at Dome C. This was followed by the collapse of the critically unstable Conger Ice Shelf. More than 100 daily low sea-ice extent and sea-ice area records were set in 2022, including two new all-time annual record lows in net sea-ice extent and area in February. Across the world’s oceans, global mean sea level was record high for the 11th consecutive year, reaching 101.2 mm above the 1993 average when satellite altimetry measurements began, an increase of 3.3±0.7 over 2021. Globally-averaged ocean heat content was also record high in 2022, while the global sea-surface temperature was the sixth highest on record, equal with 2018. Approximately 58% of the ocean surface experienced at least one marine heatwave in 2022. In the Bay of Plenty, New Zealand’s longest continuous marine heatwave was recorded. A total of 85 named tropical storms were observed during the Northern and Southern Hemisphere storm seasons, close to the 1991–2020 average of 87. There were three Category 5 tropical cyclones across the globe—two in the western North Pacific and one in the North Atlantic. This was the fewest Category 5 storms globally since 2017. Globally, the accumulated cyclone energy was the lowest since reliable records began in 1981. Regardless, some storms caused massive damage. In the North Atlantic, Hurricane Fiona became the most intense and most destructive tropical or post-tropical cyclone in Atlantic Canada’s history, while major Hurricane Ian killed more than 100 people and became the third costliest disaster in the United States, causing damage estimated at $113 billion U.S. dollars. In the South Indian Ocean, Tropical Cyclone Batsirai dropped 2044 mm of rain at Commerson Crater in Réunion. The storm also impacted Madagascar, where 121 fatalities were reported. As is typical, some areas around the world were notably dry in 2022 and some were notably wet. In August, record high areas of land across the globe (6.2%) were experiencing extreme drought. Overall, 29% of land experienced moderate or worse categories of drought during the year. The largest drought footprint in the contiguous United States since 2012 (63%) was observed in late October. The record-breaking megadrought of central Chile continued in its 13th consecutive year, and 80-year record-low river levels in northern Argentina and Paraguay disrupted fluvial transport. In China, the Yangtze River reached record-low values. Much of equatorial eastern Africa had five consecutive below-normal rainy seasons by the end of 2022, with some areas receiving record-low precipitation totals for the year. This ongoing 2.5-year drought is the most extensive and persistent drought event in decades, and led to crop failure, millions of livestock deaths, water scarcity, and inflated prices for staple food items. In South Asia, Pakistan received around three times its normal volume of monsoon precipitation in August, with some regions receiving up to eight times their expected monthly totals. Resulting floods affected over 30 million people, caused over 1700 fatalities, led to major crop and property losses, and was recorded as one of the world’s costliest natural disasters of all time. Near Rio de Janeiro, Brazil, Petrópolis received 530 mm in 24 hours on 15 February, about 2.5 times the monthly February average, leading to the worst disaster in the city since 1931 with over 230 fatalities. On 14–15 January, the Hunga Tonga-Hunga Ha'apai submarine volcano in the South Pacific erupted multiple times. The injection of water into the atmosphere was unprecedented in both magnitude—far exceeding any previous values in the 17-year satellite record—and altitude as it penetrated into the mesosphere. The amount of water injected into the stratosphere is estimated to be 146±5 Terragrams, or ∼10% of the total amount in the stratosphere. It may take several years for the water plume to dissipate, and it is currently unknown whether this eruption will have any long-term climate effect.

Abstract: In Staphylococcus aureus, fhuCBG encodes an ATP-binding cassette (ABC) transporter that is required for the transport of iron(III)-hydroxamates; mutation of either fhuB or fhuG eliminates transport. In this paper, we describe construction and characterization of an S. aureus fhuCBG deletion strain. The Δ fhuCBG :: ermC mutation not only resulted in a strain that was incapable of growth on iron(III)-hydroxamates as a sole source of iron but also resulted in a strain which had a profound growth defect in iron-restricted laboratory media. The growth defect was not a result of the inability to transport iron(III)-hydroxamates since S. aureus fhuG ::Tn 917 and S. aureus fhuD1 ::Km fhuD2 ::Tet mutants, which are also unable to transport iron(III)-hydroxamates, do not have similar iron-restricted growth defects. Complementation experiments demonstrated that the growth defect of the Δ fhuCBG :: ermC mutant was the result of the inability to express FhuC and that this was the result of an inability to transport iron complexed to the S. aureus siderophore staphylobactin. Transport of iron(III)-staphylobactin is dependent upon SirA (binding protein), SirB (permease), and SirC (permease). S. aureus expressing FhuC with a Walker A K42N mutation could not utilize iron(III)-hydroxamates or iron(III)-staphylobactin as a sole source of iron, supporting the conclusion that FhuC, as expected, functions with FhuB, FhuG, and FhuD1 or FhuD2 to transport iron(III)-hydroxamates and is the “genetically unlinked” ABC-ATPase that functions with SirA, SirB, and SirC to transport iron(III)-staphylobactin. Finally, we demonstrated that the Δ fhuCBG :: ermC strain had decreased virulence in a murine kidney abscess model.

Abstract: Staphylococcus aureus SirA was previously identified as a lipoprotein, and SirB and SirC are thought to encode the transmembrane domains of an ABC transporter. Sir proteins show similarity to iron-siderophore transporters in several bacteria. Here, we show that the iron-regulated sirABC operon is divergently transcribed from the sbn operon that encodes enzymes involved in the synthesis of staphylobactin, a recently described siderophore produced by S. aureus . Mutation of either sirA or sirB increased the resistance of iron-starved S. aureus to streptonigrin and resulted in compromised growth in iron-restricted, but not iron-rich, media. We also demonstrated that sirA and sirB mutants are compromised in the ability to transport iron complexed to staphylobactin but are not compromised for uptake of other iron complexes, such as ferric hydroxamates, ferric enterobactin, or ferric citrate. SirA- and SirB-deficient S. aureus , however, retain the ability to produce staphylobactin. Moreover, we found that transcription from the sbn operon was increased, relative to the wild type, in both sirA and sirB knockout strains, likely in response to an increased level of iron starvation in these cells. These results provide evidence of a role for these proteins in iron import in S. aureus and for full fitness of the bacterium in iron-restricted environments and demonstrate a function for S. aureus genes encoding proteins involved in the transport of an endogenously produced siderophore.

Abstract: Heteroresistance is a form of antibiotic resistance where a bacterial strain is comprised of a minor resistant subpopulation and a majority susceptible subpopulation. We showed previously that colistin heteroresistance can mediate the failure of colistin therapy in an in vivo infection model, even for isolates designated susceptible by clinical diagnostics. We sought to characterize the extent of colistin heteroresistance among the highly drug-resistant carbapenem-resistant Enterobacterales (CRE). We screened 408 isolates for colistin heteroresistance. These isolates were collected between 2012 and 2015 in eight U.S. states as part of active surveillance for CRE. Colistin heteroresistance was detected in 10.1% (41/408) of isolates, and it was more common than conventional homogenous resistance (7.1%, 29/408). Most (93.2%, 38/41) of these heteroresistant isolates were classified as colistin susceptible by standard clinical diagnostic testing. The frequency of colistin heteroresistance was greatest in 2015, the last year of the study. This was especially true among Enterobacter isolates, of which specific species had the highest rates of heteroresistance. Among Klebsiella pneumoniae isolates, which were the majority of isolates tested, there was a closely related cluster of colistin-heteroresistant ST-258 isolates found mostly in Georgia. However, cladistic analysis revealed that, overall, there was significant diversity in the genetic backgrounds of heteroresistant K. pneumoniae isolates. These findings suggest that due to being largely undetected in the clinic, colistin heteroresistance among CRE is underappreciated in the United States. IMPORTANCE Heteroresistance is an underappreciated phenomenon that may be the cause of some unexplained antibiotic treatment failures. Misclassification of heteroresistant isolates as susceptible may lead to inappropriate therapy. Heteroresistance to colistin was more common than conventional resistance and was overwhelmingly misclassified as susceptibility by clinical diagnostic testing. Higher proportions of colistin heteroresistance observed in certain Enterobacter species and clustering among heteroresistant Klebsiella pneumoniae strains may inform colistin treatment recommendations. Overall, the rate of colistin nonsusceptibility was more than double the level detected by clinical diagnostics, suggesting that the prevalence of colistin nonsusceptibility among CRE may be higher than currently appreciated in the United States.

Abstract: Molecular determinants underlying the production of siderophores in the human and animal pathogen Staphylococcus aureus and the contribution of siderophore production to the virulence of this bacterium have, until now, remained undefined. Here, we show that S. aureus strains RN6390 and Newman produce siderophore when the cells are starved for iron. We further identified and characterized a nine-gene, iron-regulated operon, designated sbn and situated between sirABC and galE on the S. aureus chromosome, that is involved in the production of a siderophore. Mutation of the sbnE gene, in both RN6390 and Newman, eliminates the ability of these strains to produce a siderophore under iron-limited growth conditions, while introduction of multicopy sbnE into sbnE mutants complemented the inability of the mutants to produce the siderophore. sbnE mutants, in both the RN6390 and Newman backgrounds, displayed a drastic growth deficiency, compared to the wild type, in iron-restricted growth medium, whereas no such deficiency was observed during growth in iron-replete medium. Complemented mutants showed a restored ability to grow under iron restriction. We further showed that an sbnE mutant was compromised in a murine kidney abscess model of S. aureus infection, illustrating the importance of siderophore production to the pathogenicity of S. aureus. sbn genes were present in all S. aureus strains tested (and all S. aureus genome sequences) but were undetectable in any of the 13 coagulase-negative staphylococci tested, including Staphylococcus epidermidis .