Researchers have developed polymeric materials that are able to kill multidrug-resistant bacteria without inducing drug resistance or toxic side effects, according to a report in Nature Communications (March 2018). The polymers, known as guanidinium-functionalized polycarbonates, contain a polycarbonate backbone to which a hydrophobic spacer group carrying a guanidinium C(NH₂)₃⁺ group is attached. The positively charged guanidinium group enables the polymer to be prepared as a water-soluble salt as well as to bind to the negatively charged cell walls of bacteria. After attachment, the polymer penetrates and crosses the cell membrane and then precipitates the proteins and genes in the cytoplasm, effectively killing the bacteria. Antibiotic resistance in bacteria is a serious problem worldwide, with the World Health Organization in January 2018 reporting 500,000 people with suspected antibiotic-resistant infections in 22 countries. See also: Antibiotic; Antibiotic resistance; Antimicrobial agents; Drug resistance; Infectious disease; Polymer

It is estimated that 1 gram of soil can be inhabited by up to 10⁹ microorganisms and approximately 60,000 bacterial species. Moreover, soil harbors a vast reservoir of antimicrobial agents, and soil-dwelling bacteria have played a key role in the introduction of antibiotics to treat infectious diseases. Because these resilient bacteria not only produce antibiotics but also are exposed to other antibiotics produced by surrounding strains in the soil, they have developed diverse mechanisms to survive the toxic antimicrobial compounds created around them. Importantly, these mechanisms of robust resistance to numerous classes of antibiotics often resemble the mechanisms of resistance identified in clinical pathogens, including those that infect humans. Thus, scientists are attempting to find possible correlations between antibiotic resistance in soil bacteria and in infectious agents in humans. If correlations can be found, investigators might be able to predict future signs of clinical resistance to certain antibiotics, providing clinicians with methods to circumvent any potential resistance that may emerge. See also: Antibiotic; Antimicrobial agents; Antimicrobial resistance; Bacteria; Clinical microbiology; Drug resistance; Infectious disease; Medical bacteriology; Microbiology; Pathogen; Soil; Soil microbiology

Soil harbors a vast reservoir of antimicrobial agents. In fact, approximately 80% of all clinically implemented antibiotics are derived from soil-dwelling bacteria. However, many bacteria have evolved methods to evade the effects of various antibiotics and thus have acquired resistance to these chemical substances. Today, the increasing resistance of many common disease-causing bacteria to antibiotics is a global health crisis. Therefore, scientists are seeking to develop new antibiotics that can overcome the resistance capabilities of numerous pathogenic bacteria. Arylomycins are considered to be among the most promising of these new compounds. See also: Antibiotic; Antibiotic resistance; Antibiotic resistance in soil bacteria; Antimicrobial agents; Bacteria; Infectious disease; Medical bacteriology; Microbiology; Pathogen; Public health; Soil; Soil microbiology

Tardigrades, also known as water bears, are hardy eight-legged microorganisms ranging in length from 0.5 millimeters to 1.5 millimeters. Well known in the animal kingdom for their resilience in the face of extreme environments, tardigrades have survived in boiling water, deep sea trenches, and even space. Although the threshold of harsh conditions that tardigrades can withstand has been heavily studied, less understood is the biological mechanisms behind this unique tardigrade tolerance. See also: Astrobiology; Deep-sea trench; Space; Space biology; Tardigrada

Humans have used dried bovine dung (manure) as a fuel source since prehistoric times. In India, for example, many people burn cow or buffalo dung for cooking fuel. This bioresource provides a low-cost fuel as well as an efficient means of waste disposal. However, in rural India, the burning of dung is simultaneously a source of hazardous indoor and outdoor air pollution, resulting from the emission of fine particulates that are 2.5 micrometers or less in diameter (PM_2.5). Such combustion byproducts are considered the most dangerous to human health, because PM_2.5 can be inhaled deep into the lungs, impairing lung function as well as and affecting other organs, such as the heart and brain, or causing cancer. See also: Air pollution; Indoor air pollution

High within the coldest and driest continent, Antarctica, lies what may be an environment too hostile to support life, according to a team of scientists from Canada and the United States. They reported finding no evidence of microbial life in the dry permafrost and underlying ice-cemented soil of University Valley, located 1700 meters above sea level in the McMurdo Dry Valleys of Antarctica, which is mostly snow-free and never gets above freezing (Journal of the International Society for Microbial Ecology, January 2016). The single drier place on Earth is generally considered to be the Atacama Desert in Chile. See also: Antarctica; Desert; Hyperaridity and the dry limits of life; Permafrost

Diauxic growth is the diphasic (two-phase) growth response seen in a culture of microorganisms making a phenotypic adaptation to the addition of a second substrate. This phenomenon was discovered and named diauxie in the early 1940s by the French biochemist Jacques Monod and is characterized by a growth phase followed by a lag, after which growth is resumed. See also: Bacterial growth; Culture

For nearly 50 years, marine chemists have generally accepted that when microscopic organic compounds in seawater, known as dissolved organic carbon (DOC), sank into the deep ocean below 1000 m in depth, they became resistant to microbial degradation (recalcitrant). Once in the deep ocean, DOC can remain there for hundreds or even thousands of years. As a result, while most organic carbon cycles rapidly through nature, DOC in the deep ocean accumulates and only slowly is recycled to living things, the soil, and the air. Why this deep-ocean DOC is so stable has been uncertain, but it seemed possible that marine microorganisms could not metabolize the chemical structures of the DOC. The observation led some scientists to propose methods for mitigating global warming by sequestering carbon as DOC in the deep ocean. However, recent research indicates that such efforts might not be very helpful. See also: Biogeochemistry; Ecosystem; Global warming; Marine ecology; Marine microbiology; Marine sediments; Ocean; Seawater

There has been substantial progress in the fight against certain drug-resistant organisms that cause serious, often fatal, diseases. However, two drug-resistant microbes—specifically, Candida auris (a fungal yeast) and Acinetobacter (a genus of bacteria)—are responsible for a growing number of drug-resistant infections worldwide. These organisms pose such a potential danger to the health of affected individuals that the Centers for Disease Control and Prevention (CDC) in the United States has added the microbes to its list of pathogenic organisms considered to be urgent public-health threats. [The other pathogens on the CDC's list are Clostridioides difficile (a bacterium formerly known as Clostridium difficile), Neisseria gonorrhoeae (the causative agent of gonorrhea), and various organisms belonging to the Enterobacteriaceae bacterial family.] See also: Bacteria; Candida; Clostridium; Drug resistance; Fungi; Infectious disease; Medical bacteriology; Medical mycology; Microbiology; Pathogen; Public health; Yeast

Tuberculosis (TB) is a chronic infectious disease of humans (as well as animals) primarily involving the lungs. It is caused by the tubercle bacillus Mycobacterium tuberculosis and is transmitted by pathogenic airborne droplets. Approximately 5–10% of individuals infected with the TB bacterium progress to develop the active disease, and these individuals must be treated with a combination of antibiotics, taken for several months, for effective elimination of the disease. However, treatment failure or relapse is on the rise as a result of drug-resistant strains of the M. tuberculosis organism. See also: Antibiotic; Antibiotic resistance; Antimicrobial resistance; Bacteria; Bacteriology; Clinical microbiology; Drug resistance; Lung; Medical bacteriology; Microbiology; Mycobacterial diseases; Pathogen; Tuberculosis