The mismatch repair system (mutS and mutL) in Acinetobacter baylyi ADP1.

BACKGROUND: Acinetobacter baylyi ADP1 is an ideal bacterial strain for high-throughput genetic analysis as the bacterium is naturally transformable. Thus, ADP1 can be used to investigate DNA mismatch repair, a mechanism for repairing mismatched bases. We used the mutS deletion mutant (XH439) and mutL deletion mutant (XH440), and constructed a mutS mutL double deletion mutant (XH441) to investigate the role of the mismatch repair system in A. baylyi. RESULTS: We determined the survival rates after UV irradiation and measured the mutation frequencies, rates and spectra of wild-type ADP1 and mutSL mutant via rifampin resistance assay (RifR assay) and experimental evolution. In addition, transformation efficiencies of genomic DNA in ADP1 and its three mutants were determined. Lastly, the relative growth rates of the wild type strain, three constructed deletion mutants, as well as the rifampin resistant mutants obtained from RifR assays, were measured. All three mutants had higher survival rates after UV irradiation than wild type, especially the double deletion mutant. Three mutants showed higher mutation frequencies than ADP1 and favored transition mutations in RifR assay. All three mutants showed increased mutation rates in the experimental evolution. However, only XH439 and XH441 had higher mutation rates than the wild type strain in RifR assay. XH441 showed higher transformation efficiency than XH438 when donor DNA harbored transition mutations. All three mutants showed higher growth rates than wild-type, and these four strains displayed higher growth rates than almost all their rpoB mutants. The growth rate results showed different amino acid mutations in rpoB resulted in different extents of reduction in the fitness of rifampin resistant mutants. However, the fitness cost brought by the same mutation did not vary with strain background. CONCLUSIONS: We demonstrated that inactivation of both mutS and mutL increased the mutation rates and frequencies in A. baylyi, which would contribute to the evolution and acquirement of rifampicin resistance. The mutS deletion is also implicated in increased mutation rates and frequencies, suggesting that MutL may be activated even in the absence of mutS. The correlation between fitness cost and rifampin resistance mutations in A. baylyi is firstly established.

Photolyases and Cryptochromes in UV-resistant Bacteria from High-altitude Andean Lakes.

"High-altitude Andean Lakes" (HAAL) are pristine environments harboring poly-extremophilic microbes that show combined adaptations to physical and chemical stress such as large daily ambient thermal amplitude, extreme solar radiation levels, intense dryness, alkalinity, high concentrations of arsenic (up to 200 ppm) and dissolved salts. In this work, we compared the UV resistance profiles, pigment content and photoreactivation abilities of three UV-resistant bacteria isolated from distinct niches from HAALs, that is Acinetobacter sp. Ver3 (water, Lake Verde; 4400 m), Exiguobacterium sp. S17 (stromatolite, Lake Socompa, 3570 m) and Nesterenkonia sp. Act20 (soil, Lake Socompa, 3570 m). UV resistance ability of HAAL's strains indicate a clear adaptation to high radiation exposure encountered in their original habitat, which can be explained by genetic and physiological mechanisms named as the UV-resistome. Thus, the UV-resistome depends on the expression of a diverse set of genes devoted to evading or repairing the damage it provoked direct or indirectly. As pigment extraction and photoreactive assays indicate the presence of photoactive molecules, we characterized more in detail proteins with homology to photolyases/cryptochromes members (CPF). Phylogenetic analyses, sequence comparison and 3D modeling with bona fide CPF members were used to prove the presence of functional domains and key residues in the novel proteins.

Enhanced disinfection leads to reduction of microbial contamination and a decrease in patient colonization and infection.

In this prospective study, we monitored 4 epidemiologically important pathogens (EIPs): methicillin-resistane Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), Clostridium difficile, and multidrug-resistant (MDR) Acinetobacter to assess the effectiveness of 3 enhanced disinfection strategies for terminal room disinfection against standard practice. Our data demonstrated that a decrease in room contamination with EIPs of 94% was associated with a 35% decrease in subsequent patient colonization and/or infection.

Ultraviolet-C light as a means of disinfecting anesthesia workstations.

BACKGROUND: Anesthesia workstations (AWs) are a reservoir for pathogenic organisms potentially associated with surgical site infections. This study examined the effectiveness of the Tru-D SmartUVC device (Tru-D LLC, Nashville, TN) on bioburden reduction (BR) on AWs. METHODS: Strips of tissue inoculated with a known concentration of either Staphylococcus aureus, Enterococcus faecalis, or Acinetobacter sp were placed on 22 high-touch surfaces of an AW. Half of the AW surfaces received direct ultraviolet (UV) light exposure and half received indirect exposure. Two inoculated strips, in sterile tubes outside of the room, represented the control. Trials were conducted on AWs in an operating room and a small room. Strips were placed in a saline solution, vortexed, and plated on blood agar to assess BR by the number of colony forming units. RESULTS: All experimental trials, compared with controls, exhibited a BR >99%. There was a significantly greater reduction of E faecalis colony forming units in the operating room AW under direct exposure (P = .019) compared with indirect exposure. There was no significant difference in reduction when comparing AWs between rooms. CONCLUSION: Regardless of room size and exposure type, automated UV-C treatment greatly influences BR on AW high-touch surfaces. Hospitals instituting an automated UV-C system as an infection prevention adjunct should consider utilizing it in operating rooms for BR as part of a horizontal infection prevention surgical site infection-reduction strategy.

Costs and benefits of natural transformation in Acinetobacter baylyi.

BACKGROUND: Natural transformation enables acquisition of adaptive traits and drives genome evolution in prokaryotes. Yet, the selective forces responsible for the evolution and maintenance of natural transformation remain elusive since taken-up DNA has also been hypothesized to provide benefits such as nutrients or templates for DNA repair to individual cells. RESULTS: We investigated the immediate effects of DNA uptake and recombination on the naturally competent bacterium Acinetobacter baylyi in both benign and genotoxic conditions. In head-to-head competition experiments between DNA uptake-proficient and -deficient strains, we observed a fitness benefit of DNA uptake independent of UV stress. This benefit was found with both homologous and heterologous DNA and was independent of recombination. Recombination with taken-up DNA reduced survival of transformed cells with increasing levels of UV-stress through interference with nucleotide excision repair, suggesting that DNA strand breaks occur during recombination attempts with taken-up DNA. Consistent with this, we show that absence of RecBCD and RecFOR recombinational DNA repair pathways strongly decrease natural transformation. CONCLUSIONS: Our data show a physiological benefit of DNA uptake unrelated to recombination. In contrast, recombination during transformation is a strand break inducing process that represents a previously unrecognized cost of natural transformation.

Novel heterologous bacterial system reveals enhanced susceptibility to DNA damage mediated by yqgF, a nearly ubiquitous and often essential gene.

Despite its presence in most bacteria, yqgF remains one of only 13 essential genes of unknown function in Escherichia coli. Predictions of YqgF function often derive from sequence similarity to RuvC, the canonical Holliday junction resolvase. To clarify its role, we deleted yqgF from a bacterium where it is not essential, Acinetobacter baylyi ADP1. Loss of yqgF impaired growth and increased the frequency of transformation and allelic replacement (TAR). When E. coli yqgF was inserted in place of its A. baylyi chromosomal orthologue, wild-type growth and TAR were restored. Functional similarities of yqgF in both gamma-proteobacteria were further supported by defective 16S rRNA processing by the A. baylyi mutant, an effect previously shown in E. coli for a temperature-sensitive yqgF allele. However, our data question the validity of deducing YqgF function strictly by comparison to RuvC. A. baylyi studies indicated that YqgF and RuvC can function in opposition to one another. Relative to the wild type, the ΔyqgF mutant had increased TAR frequency and increased resistance to nalidixic acid, a DNA-damaging agent. In contrast, deletion of ruvC decreased TAR frequency and lowered resistance to nalidixic acid. YqgF, but not RuvC, appears to increase bacterial susceptibility to DNA damage, including UV radiation. Nevertheless, the effects of yqgF on growth and TAR frequency were found to depend on amino acids analogous to catalytically required residues of RuvC. This new heterologous system should facilitate future yqgF investigation by exploiting the viability of A. baylyi yqgF mutants. In addition, bioinformatic analysis showed that a non-essential gene immediately upstream of yqgF in A. baylyi and E. coli (yqgE) is similarly positioned in most gamma- and beta-proteobacteria. A small overlap in the coding sequences of these adjacent genes is typical. This conserved genetic arrangement raises the possibility of a functional partnership between yqgE and yqgF.

Variación diurna en la composición del bacterioplancton y daño del ADN en la comunidad microbiana de un lago oligotrófico andino / Diurnal variation in bacterioplankton composition and DNA damage in the microbial community from an Andean oligotrophic lake

Laguna Azul is an oligotrophic lake situated at 4,560 m above sea level and subject to a high level of solar radiation. Bacterioplankton community composition (BCC) was analysed by denaturing gradient gel electrophoresis and the impact of solar ultraviolet radiation was assessed by measuring cyclobutane pyrimidine dimers (CPD). Furthermore, pure cultures of Acinetobacter johnsonii A2 and Rhodococcus sp. A5 were exposed simultaneously and CPD accumulation was studied. Gel analyses generated a total of 7 sequences belonging to Alpha-proteobacteria (1 band), Beta-proteobacteria (1 band), Bacteroidetes (2 bands), Actinobacteria (1 band), and Firmicutes (1 band). DGGE profiles showed minimal changes in BCC and no CPD was detected even though a high level of damage was found in biodosimeters. A. johnsonii A2 showed low level of DNA damage while Rhodococcus sp. A5 exhibited high resistance since no CPD were detected under natural UV-B exposure, suggesting that the bacterial community is well adapted to this highly solar irradiated environment.

La Laguna Azul es un ambiente oligotrófico localizado a 4560m de altura y sometido a elevados niveles de radiación solar. La composición de su comunidad bacterioplanctónica fue analizada empleando la técnica de electroforesis en gradiente desnaturalizante y se investigó el impacto de la radiación ultravioleta cuantificando los dímeros de pirimidina (CPD). Además, se expusieron simultáneamente cultivos puros de Acinetobacter johnsonii A2 y Rhodococcus sp. A5 para estudiar la acumulación de CPD. El análisis de los geles mostró siete secuencias pertenecientes a Alpha-proteobacteria (1 banda), Beta-proteobacteria (1 banda), Bacteroidetes (2 bandas), Actinobacteria (1 banda) y Firmicutes (1 banda). A lo largo del día se observaron cambios mínimos en la composición de la comunidad y no se detectaron CPD. A. johnsonii A2 presentó un daño bajo mientras que Rhodococcus sp. A5 no presentó daño en su ADN, sugiriendo que la comunidad bacteriana está muy bien adaptada a este ambiente altamente irradiado

First characterisation of a CPD-class I photolyase from a UV-resistant extremophile isolated from High-Altitude Andean Lakes.

UV-resistant Acinetobacter sp. Ver3 isolated from High-Altitude Andean Lakes (HAAL) in Argentinean Puna, one of the highest UV exposed ecosystems on Earth, showed efficient DNA photorepairing ability, coupled to highly efficient antioxidant enzyme activities in response to UV-B stress. We herein present the cloning, expression, and functional characterization of a cyclobutane pyrimidine dimer (CPD)-class I photolyase (Ver3Phr) from this extremophile to prove its involvement in the previously noted survival capability. Spectroscopy of the overexpressed and purified protein identified flavin adenine dinucleotide (FAD) and 5,10-methenyltetrahydrofolate (MTHF) as chromophore and antenna molecules, respectively. All functional analyses were performed in parallel with the ortholog E. coli photolyase. Whereas the E. coli enzyme showed the FAD chromophore as a mixture of oxidised and reduced states, the Ver3 chromophore always remained partly (including the semiquinone state) or fully reduced under all experimental conditions tested. Functional complementation of Ver3Phr in Phr(-)-RecA E. coli strains was assessed by traditional UFC counting and measurement of DNA bipyrimidine photoproducts by HPLC coupled with electrospray ionisation-tandem mass spectrometry (ESI-MS/MS) detection. The results identified strong photoreactivation ability in vivo of Ver3Phr while its nonphotoreactivation function, probably related with the stimulation of nucleotide excision repair (NER), was not as manifest as for EcPhr. Whether this is a question of the approach using an exogenous photolyase incorporated in a non-genuine host or a fundamental different behaviour of a novel enzyme from an exotic environment will need further studies.

Blue-light-dependent inhibition of twitching motility in Acinetobacter baylyi ADP1: additive involvement of three BLUF-domain-containing proteins.

Twitching motility in Acinetobacter baylyi ADP1 is inhibited by moderate intensities of blue light in a temperature-dependent manner (maximally at 20 °C). We analysed the involvement of four predicted blue-light sensing using flavin (BLUF)-domain-containing proteins encoded in the genome of this strain in the twitching motility phenotype. All four genes were expressed both in light and in darkness. A phylogenetic tree showed that one BLUF domain, ACIAD2110, grouped separately from the other three (ACIAD1499, ACIAD2125 and ACIAD2129). Individual knockout mutants of the latter three, but not of ACIAD2110, fully abolished the light dependency of the twitching motility response. Quantitative analysis of transcript level of the three genes showed a decreased expression in the light, with dark/light ratios of 1.65±0.28, 1.79±0.21 and 2.69±0.39, for ACIAD2125, ACIAD2129 and ACIAD1499, respectively. Double and triple knockouts of ACIAD1499, ACIAD2125 and ACIAD2129 confirmed the same phenotype as the corresponding single knockouts. Complementation of all the single knockouts and the triple knockout mutants with any of the three BLUF-domain-encoding genes fully restored the inhibition of twitching motility by blue light that is observed in the wild-type strain. A. baylyi ADP1 therefore shows a high degree of redundancy in the genes that encode BLUF-containing photoreceptors. Moreover, all plasmid-complemented strains, expressing any of the BLUF proteins irrespective of the specific set of deleted photoreceptors, displayed increased light-dependent inhibition of twitching motility, as compared to the wild-type (P<0.001). We conclude that the three genes ACIAD1499, ACIAD2125 and ACIAD2129 are jointly required to inhibit twitching motility under moderate blue-light illumination.

First UK evaluation of an automated ultraviolet-C room decontamination device (Tru-D™).

Tru-D™ is an automated room disinfection device that uses ultraviolet-C radiation to kill micro-organisms. The device was deployed in six side-rooms and an operating theatre. In a cleaned, unoccupied operating theatre, Tru-D eradicated all organisms from the environment. Using artificially seeded Petri dishes with meticillin-resistant Staphylococcus aureus, multi-resistant acinetobacter and vancomycin-resistant enterococci, the mean log10 reductions were between three and four when used at 22,000µWs/cm(2) reflected dose. The device was easy to transport and utilize, and able to disinfect rooms rapidly. This appears to be a practical alternative technology to other 'no-touch' automated room disinfection systems.

The Acinetobacter regulatory UmuDAb protein cleaves in response to DNA damage with chimeric LexA/UmuD characteristics.

In the DNA damage response of most bacteria, UmuD forms part of the error-prone (UmuD'(2) )C polymerase V and is activated for this function by self-cleavage after DNA damage. However, the umuD homolog (umuDAb) present throughout the Acinetobacter genus encodes an extra N-terminal region, and in Acinetobacter baylyi, regulates transcription of DNA damage-induced genes. UmuDAb expressed in cells was correspondingly larger (24 kDa) than the Escherichia coli UmuD (15 kDa). DNA damage from mitomycin C or UV exposure caused UmuDAb cleavage in both E. coli wild-type and ΔumuD cells on a timescale resembling UmuD, but did not require UmuD. Like the self-cleaving serine proteases LexA and UmuD, UmuDAb required RecA for cleavage. This cleavage produced a UmuDAb' fragment of a size consistent with the predicted cleavage site of Ala83-Gly84. Site-directed mutations at Ala83 abolished cleavage, as did mutations at either the Ser119 or Lys156 predicted enzymatic residues. Co-expression of the cleavage site mutant and an enzymatic mutant did not allow cleavage, demonstrating a strictly intramolecular mechanism of cleavage that more closely resembles the LexA-type repressors than UmuD. These data show that UmuDAb undergoes a post-translational, LexA-like cleavage event after DNA damage, possibly to achieve its regulatory action.

Extremophilic Acinetobacter strains from high-altitude lakes in Argentinean Puna: remarkable UV-B resistance and efficient DNA damage repair.

High-Altitude Andean Lakes (HAAL) of the South American Andes are almost unexplored ecosystems of shallow lakes. The HAAL are recognized by a remarkably high UV exposure, strong changes in temperature and salinity, and a high content of toxic elements, especially arsenic. Being exposed to remarkably extreme conditions, they have been classified as model systems for the study of life on other planets. Particularly, Acinetobacter strains isolated from the HAAL were studied for their survival competence under strong UV-B irradiation. Clinical isolates, Acinetobacter baumannii and Acinetobacter johnsonii, served as reference material. Whereas the reference strains rapidly lost viability under UV-B irradiation, most HAAL-derived strains readily survived this exposure and showed less change in cell number after the treatment. Controls for DNA repair activity, comparing dark repair (DR) or photo repair (PR), gave evidence for the involvement of photolyases in the DNA repair. Comparative measurements by HPLC-mass spectrometry detected the number of photoproducts: bipyrimidine dimers under both PR and DR treatments were more efficiently repaired in the HAAL strains (up to 85 % PR and 38 % DR) than in the controls (31 % PR and zero DR ability). Analysis of cosmid-cloned total genomic DNA from the most effective DNA-photorepair strain (Ver3) yielded a gene (HQ443199) encoding a protein with clear photolyase signatures belonging to class I CPD-photolyases. Despite the relatively low sequence similarity of 41 % between the enzymes from Ver3 and from E. coli (PDB 1DNPA), a model-building approach revealed a high structural homology to the CPD-photolyase of E. coli.

Genome shuffling improves production of the low-temperature alkalophilic lipase by Acinetobacter johnsonii.

The production of a low-temperature alkalophilic lipase from Acinetobacter johnsonii was improved using genome shuffling. The starting populations, obtained by UV irradiation and diethyl sulfate mutagenesis, were subjected to recursive protoplast fusion. The optimal conditions for protoplast formation and regeneration were 0.15 mg lysozyme/ml for 45 min at 37°C. The protoplasts were inactivated under UV for 20 min or heated at 60°C for 60 min and a fusant probability of ~98% was observed. The positive colonies were created by fusing the inactivated protoplasts. After two rounds of genome shuffling, one strain, F22, with a lipase activity of 7 U/ml was obtained.

Diverse responses to UV light exposure in Acinetobacter include the capacity for DNA damage-induced mutagenesis in the opportunistic pathogens Acinetobacter baumannii and Acinetobacter ursingii.

Error-prone and error-free DNA damage repair responses that are induced in most bacteria after exposure to various chemicals, antibiotics or radiation sources were surveyed across the genus Acinetobacter. The error-prone SOS mutagenesis response occurs when DNA damage induces a cell's umuDC- or dinP-encoded error-prone polymerases. The model strain Acinetobacter baylyi ADP1 possesses an unusual, regulatory umuD allele (umuDAb) with an extended 5' region and only incomplete fragments of umuC. Diverse Acinetobacter species were investigated for the presence of umuDC and their ability to conduct UV-induced mutagenesis. Unlike ADP1, most Acinetobacter strains possessed multiple umuDC loci containing either umuDAb or a umuD allele resembling that of Escherichia coli. The nearly omnipresent umuDAb allele was the ancestral umuD in Acinetobacter, with horizontal gene transfer accounting for over half of the umuDC operons. Despite multiple umuD(Ab)C operons in many strains, only three species conducted UV-induced mutagenesis: Acinetobacter baumannii, Acinetobacter ursingii and Acinetobacter beijerinckii. The type of umuDC locus or mutagenesis phenotype a strain possessed was not correlated with its error-free response of survival after UV exposure, but similar diversity was apparent. The survival of 30 Acinetobacter strains after UV treatment ranged over five orders of magnitude, with the Acinetobacter calcoaceticus-A. baumannii (Acb) complex and haemolytic strains having lower survival than non-Acb or non-haemolytic strains. These observations demonstrate that a genus can possess a range of DNA damage response mechanisms, and suggest that DNA damage-induced mutation could be an important part of the evolution of the emerging pathogens A. baumannii and A. ursingii.

Physiological and metabolic responses for hexadecane degradation in Acinetobacter oleivorans DR1.

The hexadecane degradation of Acinetobacter oleivorans DR1 was evaluated with changes in temperature and ionic salt contents. Hexadecane degradation of strain DR1 was reduced markedly by the presence of sodium chloride (but not potassium chloride). High temperature (37°C) was also shown to inhibit the motility, biofilm formation, and hexadecane biodegradation. The biofilm formation of strain DR1 on the oil-water interface might prove to be a critical physiological feature for the degradation of hexadecane. The positive relationship between biofilm formation and hexadecane degradation could be observed at 30° C, but not at low temperatures (25°C). Alterations in cell hydrophobicity and EPS production by temperature and salts were not correlated with biofilm formation and hexadecane degradation. Our proteomic analyses have demonstrated that metabolic changes through the glyoxylate pathway are important for efficient degradation of hexadecane. Proteins involved in fatty acid metabolism, gluconeogenesis, and oxidative stress defense proteins appear to be highly expressed during biodegradation of hexadecane. These results suggested that biofilm formation and oxidative stress defense are important physiological responses for hexadecane degradation along with metabolic switch to glyoxylate pathway in strain DR1.

UV-resistant Acinetobacter sp. isolates from Andean wetlands display high catalase activity.

Andean wetlands are characterized by their extreme environmental conditions such as high UV radiation, elevated heavy metal content and salinity. We present here the first study on UV tolerance and antioxidant defense of four Acinetobacter strains: Ver3, Ver5 and Ver7, isolated from Lake Verde, and N40 from Lake Negra, both lakes located 4400 m above sea level. All four isolates displayed higher UV resistance compared with collection strains, with Ver3 and Ver7 being the most tolerant strains not only to UV radiation but also to hydrogen peroxide (H(2)O(2)) and methyl viologen (MV) challenges. A single superoxide dismutase band with similar activity was detected in all studied strains, whereas different electrophoretic pattern and activity levels were observed for catalase. Ver3 and Ver7 displayed 5-15 times higher catalase activity levels than the control strains. Analysis of the response of antioxidant enzymes to UV and oxidative challenges revealed a significant increase in Ver7 catalase activity after H(2)O(2) and MV exposure. Incubation of Ver7 cultures with a catalase inhibitor resulted in a significant decrease of tolerance against UV radiation. We conclude that the high catalase activity displayed by Ver7 isolate could play an important role in UV tolerance.

Prokaryotic phototaxis.

Microorganisms have various mechanisms at their disposal to react to (changes in) their ambient light climate (i.e., intensity, color, direction, and degree of polarization). Of these, one of the best studied mechanisms is the process of phototaxis. This process can be described as a behavioral migration-response of an organism toward a change in illumination regime. In this chapter we discuss three of these migration responses, based on swimming, swarming, and twitching motility, respectively. Swimming motility has been studied using a wide range of techniques, usually microscopy based. We present a detailed description of the assays used to study phototaxis in liquid cultures of the phototrophic organisms Halobacterium salinarum, Halorhodospira halophila, and Rhodobacter sphaeroides and briefly describe the molecular basis of these responses. Swarming and twitching motility are processes taking place at the interface between a solid phase and a liquid or gas phase. Although assays to study these processes are relatively straightforward, they are accompanied by technical complications, which we describe. Furthermore, we discuss the molecular processes underlying these forms of motility in Rhodocista centenaria and Synechocystis PCC6803. Recently, it has become clear that also chemotrophic organisms contain photoreceptor proteins that allow them to respond to their ambient light climate. Surprisingly, light-modulated motility responses can also be observed in the chemotrophic organisms Escherichia coli and Acinetobacter calcoaceticus. In the light-modulated surface migration not only "che-like" signal transduction reactions may play a role, but in addition processes as modulation of gene expression and even intermediary metabolism.

Radiation sensitivity of Acinetobacter spp. and their redicidation for preservation of meat at low temperature.

In recent years, interest has been growing to preserve food including meat applying gamma radiation recommended by International Atomic Energy Agency to extend the shelf-life of meat retaining the organoleptic conditions as it is. In view of this point the present study aims to check the sensitivity of Acinetobacter spp. isolated from meat to gamma radiations. Seven species of Acinetobacter viz. A. lwoffli M1; A. baumannii M8; A. calcoaceticus M19; A. junii M20; A. johnsonnii M23; A. haemolyticus M27 and A. radioresistens M25 isolated from meat were exposed to gamma radiation at the dose level of 0.1 to 10 KGy. The D10 value of Acinetobacter was found highest 1.25 KGy in A. radioresistens M25, which was 4 to 8 times higher than other genospecies of Acinetobacter. Acinetobacter radioresistens M25 contains one plasmid of 45 Kb. The radicidation dose of 4 KGy gamma radiations was found to be sufficient to eliminate the natural contamination of meat and contamination by Acinetobacter. To eliminate radiation resistant Acinetobacter contamination a dose of 4 to 5 KGy was required. Development of the radicidation process for preservation of meat to eliminate Acinetobacter as contaminants at low temperature is one of the new and interesting phenomena. Attempts of finding the appropriate radicidation dose for preservation of meat at low temperature will open up new avenues for commercial preservation of meat.

Sensitivity of an Acinetobacter baylyi mpl mutant to DNA damage.

A mutant derived from Acinetobacter baylyi ADP1 was isolated from a screen for genes involved in the response to DNA damage. This derivative has an insertion in the mpl gene which encodes a peptidoglycan-recycling protein. We demonstrate that the insertion renders cells sensitive to mitomycin C and to UV.